Raina Margaret Maier

Interests

Research

Bacterial diversity and function in extremely oligotrophic environments such as deserts, mine tailings,desert caves;Phytostabilization of mine tailings;Microbial surfactants (biosurfactants) discovery and applications.

Teaching

SWES 425/525 Environmental MicrobiologySWES 440/540 Biodegradation of Pollutants in Soil and WaterSWES 696c Topics in Mine Reclamation and Environmental Management

Courses

Scholarly Contributions

Chapters

• Maier, R. M. (2019). Biological processes affecting contaminant transport and fate. In Environmental and Pollution Science, 3rd Edition(pp 132-148). Elsevier.
• Ortiz, M., Neilson, J. W., Legatzki, A., & Maier, R. M. (2015). Bacterial and archaeal diversity on cave speleothem and rock surfaces: A carbonate cave case study from Kartchner Caverns In: Life in Extreme Environments. In Life in Extreme Environments, Vol 3: Microbial Life of Cave Systems(pp 105-124). DeGruyter. doi:10.1515/9783110339888-007
• Hogan, D. E., Veres-Schalnat, T. A., Pemberton, J. E., & Maier, R. M. (2014). Biosurfactant Complexation of Metals and Applications for Remediation. In Research Trends and Applications. CRC Press.
• Maier, R. M. (2014). Bacterial Growth. In Environmental Microbiology. Academic Press.
• Maier, R. M. (2014). Biogeochemical Cycling. In Environmental Microbiology. Academic Press.
• Maier, R. M., & Gentry, T. J. (2014). Microorganisms and Organic Pollutants. In Environmental Microbiology. Academic Press.
• Maier, R. M., & Gentry, T. J. (2014). Physiological Methods. In Environmental Microbiology. Academic Press.
• Maier, R. M., & Neilson, J. W. (2014). Extreme Environments. In Environmental Microbiology. Academic Press.
• Maier, R. M., & Roane, T. M. (2014). Microorganisms as indicators for metal(loid) impacted environments. In Sampling and Monitoring for the Mine Life Cycle, Appendix 3(pp 182-185). Englewood,Colorado: Society for Mining, Metallurgy and Exploration, Inc.
• Pierson III, L. S., Maier, R. M., & Pepper, I. L. (2014). Microbial Communication: Bacteria/Bacteria and Bacteria/Host. In Environmental Microbiology. Academic Press.
• Rich, V. I., & Maier, R. M. (2014). Aquatic Microbiology. In Environmental Microbiology. Academic Press.
  More info

  IN PRESS - ANTICIPATED PUBLICATION SUMMER 2014. Rich, V, Maier RM. Chapter 6 - Aquatic Microbiology, In: Ian L. Pepper, Charles P. Gerba, Terry Gentry, Editor(s), Environmental Microbiology (Third Edition), Academic Press, San Diego.
• Veres-Schalnat, T. A., Pemberton, J. E., Maier, R. M., & Hogan, D. E. (2014). Biosurfactant Complexation of Metals and Applications for Remediation. In Biosurfactants: Research Trends and Applications(pp 278-310). Boca Raton: Taylor & Francis Group. doi:10.1201/b16383

Journals/Publications

• McCawley, I. A., Maier, R. M., & Hogan, D. E. (2023). Comparison of synthetic rhamnolipids as chemical precipitants for Pb, La, and Mg. Journal of hazardous materials, 447, 130801.
  More info

  Identifying and exploiting cost-effective and green methods of metal recovery from natural and contaminated aqueous systems is widely recognized as necessary to supplement the supply of critical elements, decrease the environmental impacts associated with hardrock mining, and remediate metal-contaminated waters. This research examines a novel approach based on rhamnolipid-facilitated chemical precipitation of metals. Three techniques were assessed to remove the rhamnolipid:metal complex from solution: mixing only, and mixing following by filtration or centrifugation. Recent advances in the ability to synthetically produce rhamnolipid surfactants allowed investigation of a variety of rhamnolipid structures. Rhamnolipids differing in the length and number of hydrophobic tails were assessed to remove Pb, La, and Mg from single metal solutions. In general, removal increased with increased rhamnolipid hydrophobicity and with the addition of an active removal step (filtration or centrifugation). Filtration removed up to 96% of all metals while centrifugation removed up to 97% for Pb and La and 60% for Mg. Results suggest tailoring the rhamnolipid structure and removal methods may enable selective metal removal to achieve specific outcomes. Future studies in mixed-metal and real-world solutions will be needed to confirm the viability of these techniques in complex systems.
• Ossanna, L. Q., Serrano, K., Jennings, L. L., Dillon, J., Maier, R. M., & Neilson, J. W. (2022). Progressive belowground soil development associated with sustainable plant establishment during copper mine waste revegetation. Applied Soil Ecology.
• Hammond, C. M., Root, R. A., Maier, R. M., & Chorover, J. (2022). Metal Lability and Mass Transfer Response to Direct-Planting Phytostabilization of Pyritic Mine Tailings. Minerals (Basel, Switzerland), 12(6).
  More info

  Understanding the temporal effects of organic matter input and water influx on metal lability and translocation is critical to evaluate the success of the phytostabilization of metalliferous mine tailings. Trends of metal lability, e.g., V, Cr, Mn, Co, Ni, Cu, Zn, and Pb, were investigated for three years following a direct-planting phytostabilization trial at a Superfund mine tailings site in semi-arid central Arizona, USA. Unamended tailings were characterized by high concentrations (mmol kg) of Fe (2100), S (3100), As (41), Zn (39), and Pb (11), where As and Pb greatly exceeded non-residential soil remediation levels established by Arizona. Phytostabilization treatments included a no-compost control, 100 g kg compost with seed, and 200 g kg compost with and without seed to the top 20 cm of the tailings profile. All plots received supplemental irrigation, effectively doubling the mean annual precipitation. Tailings cores up to 90 cm were Collected at the time of planting and every summer for 3 years. The cores were sub-sectioned at 20 cm increments and analyzed via total digestion and an operationally defined sequential extraction for elemental analysis and the calculation of a mass transfer coefficient normalized to Ti as an assigned immobile element. The results indicate that Pb was recalcitrant and relatively immobile in the tailings environment for both the uncomposted control and composted treatments with a maximum variation in the total concentration of 9-14 mmol kg among all samples. Metal lability and translocation above the redox boundary (. 30 cm depth) was governed by acid generation, where surficial pH was measured as low as 2.7 ± 0.1 in year three and strongly correlated with the increased lability of Mn, Co, Ni, Cu, and Zn. There was no significant pH effect on the lability of V, Cr, or Pb. Translocation to depths was greatest for Mn and Co; however, Zn, Ni, Cr, and Cu were also mobilized. The addition of organic matter enhanced the mobilization of Cr from the near surface to 40-60 cm depth (pH > 6) over the three-year phytostabilization study compared to the control. The increased enrichment of some metals at 60-90 cm indicates that the long-term monitoring of elemental translocation is necessary to assess the efficacy of phytostabilization to contain subsurface metal contaminants and thereby protect the surrounding community from exposure.
• Luo, J., Maier, R. M., Yu, D., Liu, B., Zhu, N., Amy, G. L., & Crittenden, J. C. (2022). Double-Network Hydrogel: A Potential Practical Adsorbent for Critical Metals Extraction and Recovery from Water. Environmental science & technology, 56(8), 4715-4717.
• Can Sener, S. E., Thomas, V. M., Hogan, D. E., Maier, R. M., Carbajales-Dale, M., Barton, M. D., Karanfil, T., Crittenden, J. C., & Amy, G. L. (2021). Recovery of Critical Metals from Aqueous Sources. ACS sustainable chemistry & engineering, 9(35), 11616-11634.
  More info

  Critical metals, identified from supply, demand, imports, and market factors, include rare earth elements (REE), platinum group metals, precious metals, and other valuable metals such as lithium, cobalt, nickel, and uranium. Extraction of metals from U.S. saline aqueous, emphasizing saline, sources is explored as an alternative to hardrock ore mining. Potential aqueous sources include seawater, desalination brines, oil-and-gas produced waters, geothermal aquifers, and acid mine drainage, among others. A feasibility assessment reveals opportunities for recovery of lithium, strontium, magnesium, and several REE from select sources, in quantities significant for U.S. manufacturing and for reduction of U.S. reliance on international supply chains. This is a conservative assessment given that water quality data are lacking for a significant number of critical metals in certain sources. The technology landscape for extraction and recovery of critical metals from aqueous sources is explored, identifying relevant processes along with knowledge gaps. Our analysis indicates that aqueous mining would result in much lower environmental impacts on water, air, and land than ore mining. Preliminary assessments of the economics and energy consumption of recovery show potential for recovery of critical metals.
• Hogan, D. E., Stolley, R. M., Boxley, C., Amistadi, M. K., & Maier, R. M. (2022). Removal of uranium from contaminated groundwater using monorhamnolipids and ion flotation. Journal of environmental management, 301, 113835.
  More info

  Mining of uranium for defense-related purposes has left a substantial legacy of pollution that threatens human and environmental health. Contaminated waters in the arid southwest are of particular concern, as water resource demand and water scarcity issues become more pronounced. The development of remediation strategies to treat uranium impacted waters will become increasingly vital to meet future water needs. Ion flotation is one technology with the potential to address legacy uranium contamination. The green biosurfactant rhamnolipid has been shown to bind uranium and act as an effective collector in ion flotation. In this study, uranium contaminated groundwater (∼440 μg L U) from the Monument Valley processing site in northeast Arizona was used as a model solution to test the uranium removal efficacy of ion flotation with biosynthetic (bio-mRL) and three synthetic monorhamnolipids with varying hydrophobic chain lengths: Rha-C10-C10, Rha-C12-C12, and Rha-C14-C14. At the groundwater's native pH 8, and at an adjusted pH 7, no uranium was removed from solution by any collector. However, at pH 6.5 bio-mRL and Rha-C10-C10 removed 239.2 μg L and 242.4 μg L of uranium, respectively. By further decreasing the pH to 5.5, bio-mRL was able to reduce the uranium concentration to near or below the Environmental Protection Agency maximum contaminant level of 30 μg L. For the Rha-C12-C12 and Rha-C14-C14 collector ligands, decreasing the pH to 7 or below reduced the foam stability and quantity, such that these collectors were not suitable for treating this groundwater. To contextualize the results, a geochemical analysis of the groundwater was conducted, and a consideration of uranium speciation is described. Based on this study, the efficacy of monorhamnolipid-based ion flotation in real world groundwater has been demonstrated with suitable solution conditions and collectors identified.
• Kushwaha, P., Neilson, J. W., Barberan, A., Chen, Y., Fontana, C. G., Butterfield, B. J., & Maier, R. M. (2021). Arid ecosystem vegetation canopy-gap dichotomy: influence on soil microbial composition and nutrient cycling functional potential. Applied and Environmental Microbiology. doi:10.1128/AEM.02780-20
• Kushwaha, P., Neilson, J. W., Maier, R. M., & Babst-Kostecka, A. (2022). Soil microbial community and abiotic soil properties influence Zn and Cd hyperaccumulation differently in Arabidopsis halleri. The Science of the total environment, 803, 150006.
  More info

  Soil contamination with trace metal(loid) elements (TME) is a global concern. This has focused interest on TME-tolerant plants, some of which can hyperaccumulate extraordinary amounts of TME into above-ground tissues, for potential treatment of these soils. However, intra-species variability in TME hyperaccumulation is not yet sufficiently understood to fully harness this potential. Particularly, little is known about the rhizosphere microbial communities associated with hyperaccumulating plants and whether or not they facilitate TME uptake. The aim of this study is to characterize the diversity and structure of Arabidopsis halleri rhizosphere-influenced and background (i.e., non-Arabidopsis) soil microbial communities in four plant populations with contrasting Zn and Cd hyperaccumulation traits, two each from contaminated and uncontaminated sites. Microbial community properties were assessed along with geographic location, climate, abiotic soil properties, and plant parameters to explain variation in Zn and Cd hyperaccumulation. Site type (TME-contaminated vs. uncontaminated) and location explained 44% of bacterial/archaeal and 28% of fungal community variability. A linear discriminant effect size (LEfSe) analysis identified a greater number of taxa defining rhizosphere microbial communities than associated background soils. Further, in TME-contaminated soils, the number of rhizosphere-defining taxa was 6-fold greater than in the background soils. In contrast, the corresponding ratio for uncontaminated sites, was 3 and 1.6 for bacteria/archaea and fungi, respectively. The variables analyzed explained 71% and 76% of the variance in Zn and Cd hyperaccumulation, respectively; however, each hyperaccumulation pattern was associated with different variables. A. halleri rhizosphere fungal richness and diversity associated most strongly with Zn hyperaccumulation, whereas soil Cd and Zn bioavailability had the strongest associations with Cd hyperaccumulation. Our results indicate strong associations between A. halleri TME hyperaccumulation and rhizosphere microbial community properties, a finding that needs to be further explored to optimize phytoremediation technology that is based on hyperaccumulation.
• Ramirez, M. D., Walls, R. L., Youens-Clark, K., Blumberg, K., Isaacs, K., Kaufmann, D. B., & Maier, R. M. (2021). Alleviating environmental health disparities through community science and data integration. Frontiers in Sustainable Food Systems.
• Ramírez-Andreotta, M. D., Walls, R., Youens-Clark, K., Blumberg, K., Isaacs, K. E., Kaufmann, D., & Maier, R. M. (2021). Alleviating Environmental Health Disparities Through Community Science and Data Integration. Frontiers in sustainable food systems, 5.
  More info

  Environmental contamination is a fundamental determinant of health and well-being, and when the environment is compromised, vulnerabilities are generated. The complex challenges associated with environmental health and food security are influenced by current and emerging political, social, economic, and environmental contexts. To solve these "wicked" dilemmas, disparate public health surveillance efforts are conducted by local, state, and federal agencies. More recently, citizen/community science (CS) monitoring efforts are providing site-specific data. One of the biggest challenges in using these government datasets, let alone incorporating CS data, for a holistic assessment of environmental exposure is data management and interoperability. To facilitate a more holistic perspective and approach to solution generation, we have developed a method to provide a common data model that will allow environmental health researchers working at different scales and research domains to exchange data and ask new questions. We anticipate that this method will help to address environmental health disparities, which are unjust and avoidable, while ensuring CS datasets are ethically integrated to achieve environmental justice. Specifically, we used a transdisciplinary research framework to develop a methodology to integrate CS data with existing governmental environmental monitoring and social attribute data (vulnerability and resilience variables) that span across 10 different federal and state agencies. A key challenge in integrating such different datasets is the lack of widely adopted ontologies for vulnerability and resiliency factors. In addition to following the best practice of submitting new term requests to existing ontologies to fill gaps, we have also created an application ontology, the Superfund Research Project Data Interface Ontology (SRPDIO).
• Sengupta, A., Volkmann, T. H., Danczak, R. E., Stegen, J. C., Dontsova, K., Abramson, N., Bugaj, A. S., Volk, M. J., Matos, K. A., Meira-Neto, A. A., Barberán, A., Neilson, J. W., Maier, R. M., Chorover, J., Troch, P. A., & Meredith, L. K. (2021). Contrasting Community Assembly Forces Drive Microbial Structural and Potential Functional Responses to Precipitation in an Incipient Soil System. Frontiers in microbiology, 12, 754698.
  More info

  Microbial communities in incipient soil systems serve as the only biotic force shaping landscape evolution. However, the underlying ecological forces shaping microbial community structure and function are inadequately understood. We used amplicon sequencing to determine microbial taxonomic assembly and metagenome sequencing to evaluate microbial functional assembly in incipient basaltic soil subjected to precipitation. Community composition was stratified with soil depth in the pre-precipitation samples, with surficial communities maintaining their distinct structure and diversity after precipitation, while the deeper soil samples appeared to become more uniform. The structural community assembly remained deterministic in pre- and post-precipitation periods, with homogenous selection being dominant. Metagenome analysis revealed that carbon and nitrogen functional potential was assembled stochastically. Sub-populations putatively involved in the nitrogen cycle and carbon fixation experienced counteracting assembly pressures at the deepest depths, suggesting the communities may functionally assemble to respond to short-term environmental fluctuations and impact the landscape-scale response to perturbations. We propose that contrasting assembly forces impact microbial structure and potential function in an incipient landscape; landscape characteristics (here homogenous parent material) drive community structure assembly, while short-term environmental fluctuations (here precipitation) shape environmental variations that are random in the soil depth profile and drive stochastic sub-population functional dynamics.
• Barberan, A., Maier, R. M., Kushwaha, P., Neilson, J. W., & Chen, Y. (2020). Life history strategies of soil microbial communities is an arid ecosystem. ISME Journal, online journal, doi.org/10.1038/s41396-020-00803-y. doi:doi.org/10.1038/s41396-020-00803-y
• Chen, Y., Neilson, J. W., Kushwaha, P., Maier, R. M., & Barberán, A. (2020). Life-history strategies of soil microbial communities in an arid ecosystem. The ISME journal.
  More info

  The overwhelming taxonomic diversity and metabolic complexity of microorganisms can be simplified by a life-history classification; copiotrophs grow faster and rely on resource availability, whereas oligotrophs efficiently exploit resource at the expense of growth rate. Here, we hypothesize that community-level traits inferred from metagenomic data can distinguish copiotrophic and oligotrophic microbial communities. Moreover, we hypothesize that oligotrophic microbial communities harbor more unannotated genes. To test these hypotheses, we conducted metagenomic analyses of soil samples collected from copiotrophic vegetated areas and from oligotrophic bare ground devoid of vegetation in an arid-hyperarid region of the Sonoran Desert, Arizona, USA. Results supported our hypotheses, as we found that multiple ecologically informed life-history traits including average 16S ribosomal RNA gene copy number, codon usage bias in ribosomal genes and predicted maximum growth rate were higher for microbial communities in vegetated than bare soils, and that oligotrophic microbial communities in bare soils harbored a higher proportion of genes that are unavailable in public reference databases. Collectively, our work demonstrates that life-history traits can distill complex microbial communities into ecologically coherent units and highlights that oligotrophic microbial communities serve as a rich source of novel functions.
• Hammond, C. M., Root, R. A., Maier, R. M., & Chorover, J. (2020). Arsenic and iron speciation and mobilization during phytostabilization of pyritic mine tailings. Geochimica et cosmochimica acta, 286, 306-323.
  More info

  Particulate and dissolved metal(loid) release from mine tailings is of concern in (semi-) arid environments where tailings can remain barren of vegetation for decades and, therefore, become highly susceptible to dispersion by wind and water. Erosive weathering of metalliferous tailings can lead to arsenic contamination of adjacent ecosystems and increased risk to public health. Management via phytostabilization with the establishment of a vegetative cap using organic amendments to enhance plant growth has been employed to reduce both physical erosion and leaching. However, prior research suggests that addition of organic matter into the oxic weathering zone of sulfide tailings has the potential to promote the mobilization of arsenate. Therefore, the objective of the current work was to assess the impacts of phytostabilization on the molecular-scale mechanisms controlling arsenic speciation and lability. These impacts, which remain poorly understood, limit our ability to mitigate environmental and human health risks. Here we report on subsurface biogeochemical transformations of arsenic and iron from a three-year phytostabilization field study conducted at a Superfund site in Arizona, USA. Legacy pyritic tailings at this site contain up to 3 g kg arsenic originating from arsenopyrite that has undergone oxidation to form arsenate-ferrihydrite complexes in the top 1 m. Tailings were amended in the top 20 cm with 100, 150, or 200 g kg (300-600 T ha) of composted organic matter and seeded with native halotolerant plant species. Treatments and an unamended control received irrigation of 360 ± 30 mm y in addition to 250 ± 160 mm y of precipitation. Cores to 1 m depth were collected annually for three years and sectioned into 20 cm increments for analysis by synchrotron iron and arsenic X-ray absorption spectroscopy (XAS) coupled with quantitative wet chemical and mass balance methods. Results revealed that > 80% of arsenic exists in ammonium oxalate-extractable and non-extractable phases, including dominantly ferrihydrite and jarosite. Arsenic release during arsenopyrite oxidation resulted in both downward translocation and As attenuation by stable Fe(oxyhydr)oxide and Fe (hydroxy)sulfate minerals over time, highlighting the need for sampling at multiple depths and time points for accurate interpretation of arsenic speciation, lability, and translocation in weathering profiles. Less than 1% of total arsenic was highly-labile, i.e. water-extractable, from all treatments, depths, and years, and more than 99% of arsenate released by arsenopyrite weathering was attenuated by association with secondary minerals. Although downward translocation of both arsenic and iron was detected during phytostabilization by temporal enrichment analysis, a similar trend was measured for the uncomposted control, indicating that organic amendment associated with phytostabilization practices did not significantly increase arsenic mobilization over non-amended controls.
• Hogan, D. E., Tian, F., Malm, S. W., Kegel, L. L., Szabo, L. Z., Hunjan, A. S., Pemberton, J. E., Klimecki, W. T., Polt, R., & Maier, R. M. (2020). Biodegradability and Toxicity of Cellobiosides and Melibiosides. Journal of surfactants and detergents, 23(4), 715-724.
  More info

  In 2014, almost 16 million tons of surfactants were used globally for cleaning and industrial applications. As a result, massive quantities disperse into environmental compartments every day. There is great market interest in developing highly biodegradable, less-toxic, and renewable alternatives to currently used petroleum-based surfactants. Glycolipid surfactants, composed of a sugar head-group and lipid tail, are effective surfactants and emulsifiers with a high tolerance to electrolytes and are easily tailored to address specific needs. The green synthesis and surfactant characteristics of a suite of cellobiosides and melibiosides were recently described. The biodegradability and toxicity of 1°-alkyl-O-cellobiosides, 2°-alkyl-O-cellobiosides, and 1°-alkyl-O-melibiosides with straight-chain alkyl tails of 8, 10, and 12 are reported in this study. Biodegradability was assessed by quantifying mineralization (CO evolution). All of the glycosides were inherently biodegradable and most were readily biodegradable according to OECD and EPA definitions. The Microtox acute toxicity assay showed both chain length and head group had significant effects on toxicity, but most of the molecules were practically non-toxic according to EPA definitions with EC values > 100 mg L. Cytotoxicity to human lung (H1299) and keratinocyte cell lines (HaCaT) was measured by xCELLigence and MTS assays. Cytotoxicity values were comparable to similar glycosides previously reported. IC values were determined but, in general, exceeded surfactant concentrations that are found in the environment. These data demonstrate the promising nature of these molecules as green alternatives to petrochemical surfactants.
• Hogan, D. E., Tian, F., Malm, S. W., Kegel, L. L., Szabo, L. Z., Hunjan, A. S., Pemberton, J. E., Klimecki, W., Polt, R. L., & Maier, R. M. (2020). Biodegradability and toxicity of cellobiosides and melibiosides. Journal of Surfactants and Detergents. doi:10.1002/jsde.12421
• Kushwaha, P., Neilson, J. W., Barberán, A., Chen, Y., Fontana, C. G., Butterfield, B. J., & Maier, R. M. (2021). Arid Ecosystem Vegetation Canopy-Gap Dichotomy: Influence on Soil Microbial Composition and Nutrient Cycling Functional Potential. Applied and environmental microbiology.
  More info

  Increasing temperatures and drought in desert ecosystems are predicted to cause decreased vegetation density combined with barren ground expansion. It remains unclear how nutrient availability, microbial diversity, and the associated functional capacity vary between vegetated-canopy and gap soils. The specific aim of this study was to characterize canopy vs gap microsite effect on soil microbial diversity, the capacity of gap soils to serve as a canopy-soil microbial reservoir, nitrogen (N)-mineralization genetic potential ( gene abundance) and urease enzyme activity, and microbial-nutrient pool associations in four arid-hyperarid geolocations of the western Sonoran Desert, Arizona (USA). Microsite combined with geolocation explained 57% and 45.8% of the observed variation in bacterial/archaeal and fungal community composition, respectively. A core microbiome of amplicon sequence variants was shared between the canopy and gap soil communities; however, canopy-soils included abundant taxa that were not present in associated gap communities, thereby suggesting that these taxa cannot be sourced from the associated gap soils. Linear mixed-effects models showed that canopy-soils have significantly higher microbial richness, nutrient content, and organic N-mineralization genetic and functional capacity. Furthermore, gene abundance was detected in all samples suggesting that is a relevant indicator of N-mineralization in deserts. Additionally, novel phylogenetic associations were observed for with the majority belonging to and uncharacterized bacteria. Thus, key N-mineralization functional capacity is associated with a dominant desert phylum. Overall, these results suggest that lower microbial diversity and functional capacity in gap soils may impact ecosystem sustainability as aridity drives open-space expansion in deserts.
• Sengupta, A., Kushwaha, P., Antonia, J., Troch, P. A., & Maier, R. M. (2020). New soil, old plants, and ubiquitous microbes: Evaluating the potential of incipient basaltic soil to support native plant growth and influence belowground soil microbial community composition. Sustainability. doi:10.3390/su12104209
• Hogan, D. E., Tian, F., Malm, S. W., Olivares, C., Palos Pacheco, R., Simonich, M. T., Hunjan, A. S., Tanguay, R. L., Klimecki, W. T., Polt, R., Pemberton, J. E., Curry, J. E., & Maier, R. M. (2019). Biodegradability and toxicity of monorhamnolipid biosurfactant diastereomers. Journal of hazardous materials, 364, 600-607.
  More info

  Synthetic monorhamnolipids differ from biologically produced material because they are produced as single congeners, depending on the β-hydroxyalkanoic acid used during synthesis. Each congener is produced as one of four possible diastereomers resulting from two chiral centers at the carbinols of the lipid tails [(R,R), (R,S), (S,R) and (S,S)]. We compare the biodegradability (CO respirometry), acute toxicity (Microtox assay), embryo toxicity (Zebrafish assay), and cytotoxicity (xCELLigence and MTS assays) of synthetic rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-C10-C10) monorhamnolipids against biosynthesized monorhamnolipid mixtures (bio-mRL). All Rha-C10-C10 diastereomers and bio-mRL were inherently biodegradable ranging from 34 to 92% mineralized. The Microtox assay showed all Rha-C10-C10 diastereomers and bio-mRL are slightly toxic according to the US EPA ecotoxicity categories with 5 min EC values ranging from 39.6 to 87.5 μM. The zebrafish assay showed that of 22 developmental endpoints tested, only mortality was observed at 120 h post fertilization; all Rha-C10-C10 diastereomers and bio-mRL caused significant mortality at 640 μM, except the Rha-C10-C10 (R,R) which showed no developmental effects. xCELLigence and MTS showed IC values ranging from 103.4 to 191.1 μM for human lung cell line H1299 after 72 h exposure. These data provide key information regarding Rha-C10-C10 diastereomers that is pertinent when considering potential applications.
• Honeker, L. K., Gullo, C. F., Neilson, J. W., Chorover, J., & Maier, R. M. (2019). Effect of Re-acidification on Buffalo Grass Rhizosphere and Bulk Microbial Communities During Phytostabilization of Metalliferous Mine Tailings. Frontiers in microbiology, 10, 1209.
  More info

  Phytostabilized highly acidic, pyritic mine tailings are susceptible to re-acidification over time despite initial addition of neutralizing amendments. Studies examining plant-associated microbial dynamics during re-acidification of phytostabilized regions are sparse. To address this, we characterized the rhizosphere and bulk bacterial communities of buffalo grass used in the phytostabilization of metalliferous, pyritic mine tailings undergoing re-acidification at the Iron King Mine and Humboldt Smelter Superfund Site in Dewey-Humboldt, AZ. Plant-associated substrates representing a broad pH range (2.35-7.76) were sampled to (1) compare the microbial diversity and community composition of rhizosphere and bulk compartments across a pH gradient, and (2) characterize how re-acidification affects the abundance and activity of the most abundant plant growth-promoting bacteria (PGPB; including N-fixing) versus acid-generating bacteria (AGB; including Fe-cycling/S-oxidizing). Results indicated that a shift in microbial diversity and community composition occurred at around pH 4. At higher pH (>4) the species richness and community composition of the rhizosphere and bulk compartments were similar, and PGPB, such as , , , , , and , were present and active in both compartments with minimal presence of AGB. In comparison, at lower pH (
• Hottenstein, J. D., Neilson, J. W., Gil-Loaiza, J., Root, R. A., White, S. A., Chorover, J., & Maier, R. M. (2019). Soil Microbiome Dynamics During Pyritic Mine Tailing Phytostabilization: Understanding Microbial Bioindicators of Soil Acidification. Frontiers in microbiology, 10, 1211.
  More info

  Challenges to the reclamation of pyritic mine tailings arise from acid generation that severely constrains the growth of natural revegetation. While acid mine drainage (AMD) microbial communities are well-studied under highly acidic conditions, fewer studies document the dynamics of microbial communities that generate acid from pyritic material under less acidic conditions that can allow establishment and support of plant growth. This research characterizes the taxonomic composition dynamics of microbial communities present during a 6-year compost-assisted phytostabilization field study in extremely acidic pyritic mine tailings. A complementary microcosm experiment was performed to identify successional community populations that enable the acidification process across a pH gradient. Taxonomic profiles of the microbial populations in both the field study and microcosms reveal shifts in microbial communities that play pivotal roles in facilitating acidification during the transition between moderately and highly acidic conditions. The potential co-occurrence of organoheterotrophic and lithoautotrophic energy metabolisms during acid generation suggests the importance of both groups in facilitating acidification. Taken together, this research suggests that key microbial populations associated with pH transitions could be used as bioindicators for either sustained future plant growth or for acid generation conditions that inhibit further plant growth.
• Rader, S., Maier, R. M., Barton, M., & Mazdab, F. (2019). Uptake and fractionation of thallium by Brassica juncea in geogenic thallium-amended substrate. Environmental science & technology.
  More info

  This study shows thallium (Tl) concentrations in Brassica juncea (Indian mustard) tissue are over an order of magnitude higher (3830 μg/kg) than the substrate (100 μg/kg) and are strongly influenced by the underlying mineralogy, i.e., Tl bioaccessibility depends on the mineral structure: K-feldspar > Mn-nodule > hendricksite mica. The majority of Tl for all substrates is contained in edible parts of the plant, i.e. leaves (41% of total Tl, on average) ≥ flower stems (34%) > seed pods (11%) ≈ stems (10%) > flowers (3%). We also show that Tl isotope fractionation induced by B. juncea is substantial, at nearly 10 ε205Tl units, and generates systematic plant-specific patterns. Progressive plant growth strongly fractionates Tl isotopes, discriminating against 205Tl as the plant matures. Thus, 205Tl values are systematically higher in the early-formed stem (ε205Tlavg = +2.5) than in plant elements formed later (ε205Tlavg = -2.5 to +0.1), which demonstrates the large degree of translocation and the associated effects during plant growth. This study establishes the potential of Tl isotopes as a new tool in understanding heavy metal (re-)distribution during anthropogenic and geologic processes and the utility of such information in environmental and health-related planning, as well as phytomining or bioprospecting.
• Sengupta, A., Stegen, J. C., Meira, N., Wang, Y., Neilsont, J. W., Chorover, J., Troch, P. A., & Maier, R. M. (2019). Assessing Microbial Community Patterns During Incipient Soil Formation From Basalt. JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES, 124(4), 941-958.
• Zaharescu, D. G., Burghelea, C. I., Dontsova, K., Presler, J. K., Hunt, E. A., Domanik, K. J., Amistadi, M. K., Sandhaus, S., Munoz, E. N., Gaddis, E. E., Galey, M., Vaquera-Ibarra, M. O., Palacios-Menendez, M. A., Castrejón-Martinez, R., Roldán-Nicolau, E. C., Li, K., Maier, R. M., Reinhard, C. T., & Chorover, J. (2019). Ecosystem-bedrock interaction changes nutrient compartmentalization during early oxidative weathering. Scientific reports, 9(1), 15006.
  More info

  Ecosystem-bedrock interactions power the biogeochemical cycles of Earth's shallow crust, supporting life, stimulating substrate transformation, and spurring evolutionary innovation. While oxidative processes have dominated half of terrestrial history, the relative contribution of the biosphere and its chemical fingerprints on Earth's developing regolith are still poorly constrained. Here, we report results from a two-year incipient weathering experiment. We found that the mass release and compartmentalization of major elements during weathering of granite, rhyolite, schist and basalt was rock-specific and regulated by ecosystem components. A tight interplay between physiological needs of different biota, mineral dissolution rates, and substrate nutrient availability resulted in intricate elemental distribution patterns. Biota accelerated CO mineralization over abiotic controls as ecosystem complexity increased, and significantly modified the stoichiometry of mobilized elements. Microbial and fungal components inhibited element leaching (23.4% and 7%), while plants increased leaching and biomass retention by 63.4%. All biota left comparable biosignatures in the dissolved weathering products. Nevertheless, the magnitude and allocation of weathered fractions under abiotic and biotic treatments provide quantitative evidence for the role of major biosphere components in the evolution of upper continental crust, presenting critical information for large-scale biogeochemical models and for the search for stable in situ biosignatures beyond Earth.
• Maier, R. M., Curry, J. E., & Hogan, D. E. (2018). Ion Flotation of La3+, Cd2+ and Cs+ using monorhamnolipid collector. Colloids and Interfaces, 2(4), 43. doi:10.3390
• Maier, R. M., Curry, J. E., & Hogan, D. E. (2018). Ion Flotation of La3+, Cd2+, and Cs+ using Monorhamnolipid Collector. Colloids and Interfaces, 2(43). doi:10.3390/colloids2040043
• Depner, M., Ege, M. J., Cox, M. J., Dwyer, S., Walker, A. W., Birzele, L. T., Genuneit, J., Horak, E., Braun-Fahrlaender, C., Danielewicz, H., Maier, R. M., Moffatt, M. F., Cookson, W. O., Heederik, D., von, M. E., & Legatzki, A. (2017). Bacterial microbiota of the upper respiratory tract and childhood asthma. JOURNAL OF ALLERGY AND CLINICAL IMMUNOLOGY, 139(3), 826-+.
• Eisman, R. J., Munusamy, E., Kegel, L. M., Hogan, D. E., Maier, R. M., Schwartz, S. D., & Pemberton, J. E. (2017). Evolution of aggregate structure in solutions of anionic monorhamnolipids: experimental and computational results. Langmuir, 33, 7412-7424.
• Eismin, R. J., Munusamy, E., Kegel, L. L., Hogan, D. E., Maier, R. M., Schwartz, S. D., & Pemberton, J. E. (2017). Evolution of Aggregate Structure in Solutions of Anionic Monorhamnolipids: Experimental and Computational Results. Langmuir : the ACS journal of surfaces and colloids, 33(30), 7412-7424.
  More info

  The evolution of solution aggregates of the anionic form of the native monorhamnolipid (mRL) mixture produced by Pseudomonas aeruginosa ATCC 9027 is explored at pH 8.0 using both experimental and computational approaches. Experiments utilizing surface tension measurements, dynamic light scattering, and both steady-state and time-resolved fluorescence spectroscopy reveal solution aggregation properties. All-atom molecular dynamics simulations on self-assemblies of the most abundant monorhamnolipid molecule, l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-C10-C10), in its anionic state explore the formation of aggregates and the role of hydrogen bonding, substantiating the experimental results. At pH 8.0, at concentrations above the critical aggregation concentration of 201 μM but below ∼7.5 mM, small premicelles exist in solution; above ∼7.5 mM, micelles with hydrodynamic radii of ∼2.5 nm dominate, although two discrete populations of larger lamellar aggregates (hydrodynamic radii of ∼10 and 90 nm) are also present in solution in much smaller number densities. The critical aggregation number for the micelles is determined to be ∼26 monomers/micelle using fluorescence quenching measurements, with micelles gradually increasing in size with monorhamnolipid concentration. Molecular dynamics simulations on systems with between 10 and 100 molecules of Rha-C10-C10 indicate the presence of stable premicelles of seven monomers with the most prevalent micelle being ∼25 monomers and relatively spherical. A range of slightly larger micelles of comparable stability can also exist that become increasing elliptical with increasing monomer number. Intermolecular hydrogen bonding is shown to play a significant role in stabilization of these aggregates. In total, the computational results are in excellent agreement with the experimental results.
• Hammond, C. M., Root, R. A., Maier, R. M., & Chorover, J. (2017). Mechanisms of arsenic sequestration by Prosopis juliflora during phytostabilization of metalliferous mine tailings. Environmental science & technology.
  More info

  Phytostabilization is a cost-effective long-term bioremediation technique for immobilization of metalliferous mine tailings. However the biogeochemical processes affecting metal(loid) molecular stabilization and mobility in the root zone remain poorly resolved. Roots of Prosopis juliflora grown for up to 36 months in compost-amended pyritic mine tailings from a federal Superfund site were investigated by micro-scale and bulk synchrotron X-ray absorption spectroscopy (XAS) and multiple energy micro X-ray fluorescence (ME-μXRF) imaging to determine iron, arsenic, sulfur speciation, abundance, and spatial distribution. Whereas ferrihydrite-bound As(V) species predominated in the initial bulk mine tailings, rhizosphere speciation of arsenic was distinctly different. Root associated As(V) was immobilized on the root epidermis bound to ferric sulfate precipitates and within root vacuoles as trivalent As(III)-SH3 complexes. Molar Fe:As ratios of root epidermis tissue was 2x times higher than the 15% compost-amended bulk tailings growth medium. Rhizoplane associated ferric sulfate phases that showed a high capacity to scavenge As(V) were dissimilar from the bulk tailings mineralogy as shown by XAS and XRD, indicating a root surface mechanism for their formation or accumulation.
• Hogan, D. E., Curry, J. E., Pemberton, J. E., & Maier, R. M. (2017). Rhamnolipid biosurfactant complexation of rare earth elements. Journal of hazardous materials, 340, 171-178.
  More info

  Rare earth elements (REE) are vital for modern technologies and considered critical materials. This study investigated monorhamnolipid biosurfactant interactions with REE as the basis for REE recovery technology. Conditional stability constants (log β), measured using a resin-based ion exchange method, are reported for 16 REE and metals. These results were combined with existing data for 10 other metals to assess comparative strength and determinants of binding. The stability constants could be divided into three groups: weakly, moderately, and strongly bound. The REE were all in the strongly bound group (UO22+, Eu3+, Nd3+, Tb3+, Dy3+, La3+, Cu2+, Al3+, Pb2+, Y3+, Pr3+, and Lu3+) with log β ranging from 9.82 to 8.20. The elements Cd2+, In3+, Zn2+, Fe3+, Hg2+, and Ca2+ were moderately bound with log β=7.17-4.10. Finally, Sr2+, Co2+, Ni2+, UO22+, Ba2+, Mn2+, Mg2+, Rb+, and K+ were weakly bound with log β=3.95-0.96. Two log β values are reported for the uranyl ion due to two distinct binding regions. A mixed metals study and associated selectivity coefficients confirmed monorhamnolipids preferentially remove metals with large log β values over those with smaller values. Preferential complexation by monorhamnolipids may constitute a green pathway for recovery of REE from alternative, non-traditional sources.
• Honeker, L. K., Neilson, J. W., Root, R. A., Gil-Loaiza, J., Chorover, J., & Maier, R. M. (2017). Bacterial Rhizoplane Colonization Patterns of Buchloe dactyloides Growing in Metalliferous Mine Tailings Reflect Plant Status and Biogeochemical Conditions. Microbial ecology, 74(4), 853-867.
  More info

  Plant establishment during phytostabilization of legacy mine tailings in semiarid regions is challenging due to low pH, low organic carbon, low nutrients, and high toxic metal(loid) concentrations. Plant-associated bacterial communities are particularly important under these harsh conditions because of their beneficial services to plants. We hypothesize that bacterial colonization profiles on rhizoplane surfaces reflect deterministic processes that are governed by plant health and the root environment. The aim of this study was to identify associations between bacterial colonization patterns on buffalo grass (Buchloe dactyloides) rhizoplanes and both plant status (leaf chlorophyll and plant cover) and substrate biogeochemistry (pH, electrical conductivity, total organic carbon, total nitrogen, and rhizosphere microbial community). Buffalo grass plants from mesocosm- and field-scale phytostabilization trials conducted with tailings from the Iron King Mine and Humboldt Smelter Superfund Site in Dewey-Humboldt, Arizona, were analyzed. These tailings are extremely acidic and have arsenic and lead concentrations of 2-4 g kg-1 substrate. Bacterial communities on rhizoplanes and in rhizosphere-associated substrate were characterized using fluorescence in situ hybridization and 16S rRNA gene amplicon sequencing, respectively. The results indicated that the metabolic status of rhizoplane bacterial colonizers is significantly related to plant health. Principal component analysis revealed that root-surface Alphaproteobacteria relative abundance was associated most strongly with substrate pH and Gammaproteobacteria relative abundance associated strongly with substrate pH and plant cover. These factors also affected the phylogenetic profiles of the associated rhizosphere communities. In summary, rhizoplane bacterial colonization patterns are plant specific and influenced by plant status and rhizosphere biogeochemical conditions.
• Neilson, J. W., Califf, K., Cardona, C., Copeland, A., van Treuren, W., Josephson, K. L., Knight, R., Gilbert, J. A., Quade, J., Caporaso, J. G., & Maier, R. M. (2017). Significant Impacts of Increasing Aridity on the Arid Soil Microbiome. mSystems, 2(3).
  More info

  Global deserts occupy one-third of the Earth's surface and contribute significantly to organic carbon storage, a process at risk in dryland ecosystems that are highly vulnerable to climate-driven ecosystem degradation. The forces controlling desert ecosystem degradation rates are poorly understood, particularly with respect to the relevance of the arid-soil microbiome. Here we document correlations between increasing aridity and soil bacterial and archaeal microbiome composition along arid to hyperarid transects traversing the Atacama Desert, Chile. A meta-analysis reveals that Atacama soil microbiomes exhibit a gradient in composition, are distinct from a broad cross-section of nondesert soils, and yet are similar to three deserts from different continents. Community richness and diversity were significantly positively correlated with soil relative humidity (SoilRH). Phylogenetic composition was strongly correlated with SoilRH, temperature, and electrical conductivity. The strongest and most significant correlations between SoilRH and phylum relative abundance were observed for , , , , and (Spearman's rank correlation [] = >0.81; false-discovery rate [] = ≤0.005), characterized by 10- to 300-fold decreases in the relative abundance of each taxon. In addition, network analysis revealed a deterioration in the density of significant associations between taxa along the arid to hyperarid gradient, a pattern that may compromise the resilience of hyperarid communities because they lack properties associated with communities that are more integrated. In summary, results suggest that arid-soil microbiome stability is sensitive to aridity as demonstrated by decreased community connectivity associated with the transition from the arid class to the hyperarid class and the significant correlations observed between soilRH and both diversity and the relative abundances of key microbial phyla typically dominant in global soils. We identify key environmental and geochemical factors that shape the arid soil microbiome along aridity and vegetation gradients spanning over 300 km of the Atacama Desert, Chile. Decreasing average soil relative humidity and increasing temperature explain significant reductions in the diversity and connectivity of these desert soil microbial communities and lead to significant reductions in the abundance of key taxa typically associated with fertile soils. This finding is important because it suggests that predicted climate change-driven increases in aridity may compromise the capacity of the arid-soil microbiome to sustain necessary nutrient cycling and carbon sequestration functions as well as vegetative cover in desert ecosystems, which comprise one-third of the terrestrial biomes on Earth.
• Neilson, J. W., Califf, K., Cardona, C., Copeland, A., van, T. W., Josephson, K. L., Knight, R., Gilbert, J. A., Quade, J., Caporaso, J. G., & Maier, R. M. (2017). Significant Impacts of Increasing Aridity on the Arid Soil Microbiome. MSYSTEMS, 2(3).
• Palos Pacheco, R., Eismin, R. J., Coss, C. S., Wang, H., Maier, R. M., Polt, R., & Pemberton, J. E. (2017). Synthesis and Characterization of Four Diastereomers of Monorhamnolipids. Journal of the American Chemical Society.
  More info

  Rhamnolipids are amphiphilic glycolipids biosynthesized by bacteria that, due to their low toxicity and biodegradability, are potential replacements for synthetic surfactants. The previously limited access to pure materials at the gram scale has hindered extensive characterization of rhamnolipid structure-performance behavior. Here, we present an efficient and versatile synthetic methodology from which four diastereomers of the most common monorhamnolipid, α-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate, are prepared and subsequently characterized. Exploration of their behavior at the air-water interface is reported and analyzed in terms of the absolute configuration of the lipid tail carbinols at pH 4.0 and 8.0. All diastereomers exhibit a minimum surface tension of about 28 mN/m without a significant difference between the protonated (nonionic) or deprotonated (anionic) states. At pH 4.0 (nonionic), all diastereomers have a critical micelle concentration (CMC) in the micromolar range. At pH 8.0 (anionic), CMC values for the (R,R), (S,S), and (S,R) diastereomers are approximately an order of magnitude higher than in their nonionic states, whereas the (R,S) diastereomer exhibits a CMC about five times larger.
• Ramirez, D. M., Vea, L., Field, J. A., Baker, P. B., Gandolfi, A. J., & Maier, R. M. (2017). Transferable Training Modules Building Environmental Education Opportunities With and for Mexican Community Health Workers (Promotores de Salud). FAMILY & COMMUNITY HEALTH, 40(4), 306-315.
• Ramírez, D. M., Vea, L., Field, J. A., Baker, P. B., Gandolfi, A. J., & Maier, R. M. (2017). Transferable Training Modules: Building Environmental Education Opportunities With and for Mexican Community Health Workers (Promotores de Salud). Family & community health, 40(4), 306-315.
  More info

  Community health workers (promotores de salud) have the ability to empower communities to mitigate negative health outcomes. Current training efforts in environmental topics are lacking. This project addressed this gap by developing 4 transferable training modules on environmental health. By applying a series of surveys, interviews, and trainings, we evaluated their relevance. Partners provided favorable feedback for 3 of the 4 modules. It was also learned that the development method could be improved by engaging technically trained promotores de salud in the role of co-creators. This project has implications for environmental justice communities as it can lessen information disparities.
• Santos, A. E., Cruz-Ortega, R., Meza-Figueroa, D., Romero, F. M., Sanchez-Escalante, J. J., Maier, R. M., Neilson, J. W., Alcaraz, L. D., & Molina Freaner, F. E. (2017). Plants from the abandoned Nacozari mine tailings: evaluation of their phytostabilization potential. PeerJ, 5, e3280.
  More info

  Phytostabilization is a remediation technology that uses plants for in-situ stabilization of contamination in soils and mine tailings. The objective of this study was to identify native plant species with potential for phytostabilization of the abandoned mine tailings in Nacozari, Sonora in northern Mexico. A flora of 42 species in 16 families of angiosperms was recorded on the tailings site and the abundance of the most common perennial species was estimated. Four of the five abundant perennial species showed evidence of regeneration: the ability to reproduce and establish new seedlings. A comparison of selected physicochemical properties of the tailings in vegetated patches with adjacent barren areas suggests that pH, electrical conductivity, texture, and concentration of potentially toxic elements do not limit plant distribution. For the most abundant species, the accumulation factor for most metals was
• Valentín-Vargas, A., Neilson, J. W., Root, R. A., Chorover, J., & Maier, R. M. (2017). Treatment impacts on temporal microbial community dynamics during phytostabilization of acid-generating mine tailings in semiarid regions. The Science of the total environment, 618, 357-368.
  More info

  Direct revegetation, or phytostabilization, is a containment strategy for contaminant metals associated with mine tailings in semiarid regions. The weathering of sulfide ore-derived tailings frequently drives acidification that inhibits plant establishment resulting in materials prone to wind and water dispersal. The specific objective of this study was to associate pyritic mine waste acidification, characterized through pore-water chemistry analysis, with dynamic changes in microbial community diversity and phylogenetic composition, and to evaluate the influence of different treatment strategies on the control of acidification dynamics. Samples were collected from a highly instrumented one-year mesocosm study that included the following treatments: 1) unamended tailings control; 2) tailings amended with 15% compost; and 3) the 15% compost-amended tailings planted with Atriplex lentiformis. Tailings samples were collected at 0, 3, 6 and 12months and pore water chemistry was monitored as an indicator of acidification and weathering processes. Results confirmed that the acidification process for pyritic mine tailings is associated with a temporal progression of bacterial and archaeal phylotypes from pH sensitive Thiobacillus and Thiomonas to communities dominated by Leptospirillum and Ferroplasma. Pore-water chemistry indicated that weathering rates were highest when Leptospirillum was most abundant. The planted treatment was most successful in disrupting the successional evolution of the Fe/S-oxidizing community. Plant establishment stimulated growth of plant-growth-promoting heterotrophic phylotypes and controlled the proliferation of lithoautotrophic Fe/S-oxidizers. The results suggest the potential for eco-engineering a microbial inoculum to stimulate plant establishment and inhibit proliferation of the most efficient Fe/S-oxidizing phylotypes.
• Zaharescu, D. G., Burghelea, C. I., Dontsova, K., Presler, J. K., Maier, R. M., Huxman, T., Domanik, K. J., Hunt, E. A., Amistadi, M. K., Gaddis, E. E., Palacios-Menendez, M. A., Vaquera-Ibarra, M. O., & Chorover, J. (2017). Ecosystem Composition Controls the Fate of Rare Earth Elements during Incipient Soil Genesis. Scientific reports, 7, 43208.
  More info

  The rare earth elements (REE) are increasingly important in a variety of science and economic fields, including (bio)geosciences, paleoecology, astrobiology, and mining. However, REE distribution in early rock-microbe-plant systems has remained elusive. We tested the hypothesis that REE mass-partitioning during incipient weathering of basalt, rhyolite, granite and schist depends on the activity of microbes, vascular plants (Buffalo grass), and arbuscular mycorrhiza. Pore-water element abundances revealed a rapid transition from abiotic to biotic signatures of weathering, the latter associated with smaller aqueous loss and larger plant uptake. Abiotic dissolution was 39% of total denudation in plant-microbes-mycorrhiza treatment. Microbes incremented denudation, particularly in rhyolite, and this resulted in decreased bioavailable solid pools in this rock. Total mobilization (aqueous + uptake) was ten times greater in planted compared to abiotic treatments, REE masses in plant generally exceeding those in water. Larger plants increased bioavailable solid pools, consistent with enhanced soil genesis. Mycorrhiza generally had a positive effect on total mobilization. The main mechanism behind incipient REE weathering was carbonation enhanced by biotic respiration, the denudation patterns being largely dictated by mineralogy. A consistent biotic signature was observed in La:phosphate and mobilization: solid pool ratios, and in the pattern of denudation and uptake.
• Depner, M., Ege, M. J., Cox, M. J., Dwyer, S., Walker, A. W., Birzele, L. T., Genuneit, J., Horak, E., Braun-Fahrländer, C., Danielewicz, H., Maier, R. M., Moffatt, M. F., Cookson, W. O., Heederik, D., von Mutius, E., & Legatzki, A. (2016). Bacterial microbiota of the upper respiratory tract and childhood asthma. The Journal of allergy and clinical immunology.
  More info

  Patients with asthma and healthy controls differ in bacterial colonization of the respiratory tract. The upper airways have been shown to reflect colonization of the lower airways, the actual site of inflammation in asthma, which is hardly accessible in population studies.
• Gil-Loaiza, J., White, S. A., Root, R. A., Solís-Dominguez, F. A., Hammond, C. M., Chorover, J., & Maier, R. M. (2016). Phytostabilization of mine tailings using compost-assisted direct planting: Translating greenhouse results to the field. The Science of the total environment, 565, 451-61.
  More info

  Standard practice in reclamation of mine tailings is the emplacement of a 15 to 90cm soil/gravel/rock cap which is then hydro-seeded. In this study we investigate compost-assisted direct planting phytostabilization technology as an alternative to standard cap and plant practices. In phytostabilization the goal is to establish a vegetative cap using native plants that stabilize metals in the root zone with little to no shoot accumulation. The study site is a barren 62-hectare tailings pile characterized by extremely acidic pH as well as lead, arsenic, and zinc each exceeding 2000mgkg(-1). The study objective is to evaluate whether successful greenhouse phytostabilization results are scalable to the field. In May 2010, a 0.27ha study area was established on the Iron King Mine and Humboldt Smelter Superfund (IKMHSS) site with six irrigated treatments; tailings amended with 10, 15, or 20% (w/w) compost seeded with a mix of native plants (buffalo grass, arizona fescue, quailbush, mountain mahogany, mesquite, and catclaw acacia) and controls including composted (15 and 20%) unseeded treatments and an uncomposted unseeded treatment. Canopy cover ranging from 21 to 61% developed after 41 months in the compost-amended planted treatments, a canopy cover similar to that found in the surrounding region. No plants grew on unamended tailings. Neutrophilic heterotrophic bacterial counts were 1.5 to 4 orders of magnitude higher after 41months in planted versus unamended control plots. Shoot tissue accumulation of various metal(loids) was at or below Domestic Animal Toxicity Limits, with some plant specific exceptions in treatments receiving less compost. Parameters including % canopy cover, neutrophilic heterotrophic bacteria counts, and shoot uptake of metal(loids) are promising criteria to use in evaluating reclamation success. In summary, compost amendment and seeding, guided by preliminary greenhouse studies, allowed plant establishment and sustained growth over 4years demonstrating feasibility for this phytostabilization technology.
• Gil-Loaiza, J., White, S. A., Root, R., Solis-Dominguez, F. A., Hammond, C. M., Chorover, J. D., & Maier, R. M. (2016). Phytostabillization of mine tailings using compost-assisted direct planting: Translating greenhouse results ot the field. Sci Tot Environ, 565, 451-461.
• Honeker, L. K., Root, R. A., Chorover, J., & Maier, R. M. (2016). Resolving colocalization of bacteria and metal(loid)s on plant root surfaces by combining fluorescence in situ hybridization (FISH) with multiple-energy micro-focused X-ray fluorescence (ME μXRF). Journal of microbiological methods, 131, 23-33.
  More info

  Metal(loid)-contamination of the environment due to anthropogenic activities is a global problem. Understanding the fate of contaminants requires elucidation of biotic and abiotic factors that influence metal(loid) speciation from molecular to field scales. Improved methods are needed to assess micro-scale processes, such as those occurring at biogeochemical interfaces between plant tissues, microbial cells, and metal(loid)s. Here we present an advanced method that combines fluorescence in situ hybridization (FISH) with synchrotron-based multiple-energy micro-focused X-ray fluorescence microprobe imaging (ME μXRF) to examine colocalization of bacteria and metal(loid)s on root surfaces of plants used to phytostabilize metalliferous mine tailings. Bacteria were visualized on a small root section using SytoBC nucleic acid stain and FISH probes targeting the domain Bacteria and a specific group (Alphaproteobacteria, Gammaproteobacteria, or Actinobacteria). The same root region was then analyzed for elemental distribution and metal(loid) speciation of As and Fe using ME μXRF. The FISH and ME μXRF images were aligned using ImageJ software to correlate microbiological and geochemical results. Results from quantitative analysis of colocalization show a significantly higher fraction of As colocalized with Fe-oxide plaques on the root surfaces (fraction of overlap 0.49±0.19) than to bacteria (0.072±0.052) (p
• Sengupta, A., Wang, Y., Meira Neto, A. A., Matos, K. A., Dontsova, K., Root, R., Neilson, J. W., Maier, R. M., Chorover, J., & Troch, P. A. (2016). Soil Lysimeter Excavation for Coupled Hydrological, Geochemical, and Microbiological Investigations. Journal of visualized experiments : JoVE.
  More info

  Studying co-evolution of hydrological and biogeochemical processes in the subsurface of natural landscapes can enhance the understanding of coupled Earth-system processes. Such knowledge is imperative in improving predictions of hydro-biogeochemical cycles, especially under climate change scenarios. We present an experimental method, designed to capture sub-surface heterogeneity of an initially homogeneous soil system. This method is based on destructive sampling of a soil lysimeter designed to simulate a small-scale hillslope. A weighing lysimeter of one cubic meter capacity was divided into sections (voxels) and was excavated layer-by-layer, with sub samples being collected from each voxel. The excavation procedure was aimed at detecting the incipient heterogeneity of the system by focusing on the spatial assessment of hydrological, geochemical, and microbiological properties of the soil. Representative results of a few physicochemical variables tested show the development of heterogeneity. Additional work to test interactions between hydrological, geochemical, and microbiological signatures is planned to interpret the observed patterns. Our study also demonstrates the possibility of carrying out similar excavations in order to observe and quantify different aspects of soil-development under varying environmental conditions and scale.
• Stein, M. M., Hrusch, C. L., Gozdz, J., Igartua, C., Pivniouk, V., Murray, S. E., Ledford, J. G., Marques dos Santos, M., Anderson, R. L., Metwali, N., Neilson, J. W., Maier, R. M., Gilbert, J. A., Holbreich, M., Thorne, P. S., Martinez, F. D., von Mutius, E., Vercelli, D., Ober, C., & Sperling, A. I. (2016). Innate Immunity and Asthma Risk in Amish and Hutterite Farm Children. The New England journal of medicine, 375(5), 411-21.
  More info

  The Amish and Hutterites are U.S. agricultural populations whose lifestyles are remarkably similar in many respects but whose farming practices, in particular, are distinct; the former follow traditional farming practices whereas the latter use industrialized farming practices. The populations also show striking disparities in the prevalence of asthma, and little is known about the immune responses underlying these disparities.
• Boxley, C. J., Boxley, C. J., Pemberton, J. E., Pemberton, J. E., Maier, R. M., & Maier, R. M. (2015). Rhamnolipids and related biosurfactants for cosmetics and cosmeceutical markets. INFORM (International News on Fats, Oils, and related Materials), 26, 206-210.
  More info

  Trade Journal article
• Burghelea, C., Burghelea, C., Zaharescu, G. D., Zaharescu, G. D., Dontsova, K. M., Dontsova, K. M., Maier, R. M., Maier, R. M., Huxman, T., Huxman, T., Chorover, J. D., & Chorover, J. D. (2015). Mineral nutrient mobilization by plants from rock: Influence of rock type and arbuscular mycorrhiza. Biogeochemistry, 124(1-3), 187-203. doi:10.1007/s10533-015-0092-5
• Burghelea, C., Zaharescu, D. G., Dontsova, K., Maier, R., Huxman, T., & Chorover, J. (2015). Mineral nutrient mobilization by plants from rock: influence of rock type and arbuscular mycorrhiza. BIOGEOCHEMISTRY, 124(1-3), 187-203.
• Landrigan, P. J., Wright, R. O., Cordero, J. F., Eaton, D. L., Goldstein, B. D., Hennig, B., Maier, R. M., Ozonoff, D. M., Smith, M. T., & Tukey, R. H. (2015). The NIEHS Superfund Research Program: 25 Years of Translational Research for Public Health. Environmental health perspectives, 123(10), 909-18.
  More info

  The Superfund Research Program (SRP) is an academically based, multidisciplinary, translational research program that for 25 years has sought scientific solutions to health and environmental problems associated with hazardous waste sites. SRP is coordinated by the National Institute of Environmental Health Sciences (NIEHS). It supports multi-project grants, undergraduate and postdoctoral training programs, individual research grants, and Small Business Innovation Research (SBIR) and Technology Transfer Research (STTR) grants.
• Nelson, K. N., Neilson, J. W., Root, R. A., Chorover, J., & Maier, R. M. (2015). Abundance and Activity of 16S rRNA, AmoA and NifH Bacterial Genes During Assisted Phytostabilization of Mine Tailings. International journal of phytoremediation, 17(1-6), 493-502.
  More info

  Mine tailings in semiarid regions are highly susceptible to erosion and are sources of dust pollution and potential avenues of human exposure to toxic metals. One constraint to revegetation of tailings by phytostabilization is the absence of microbial communities critical for biogeochemical cycling of plant nutrients. The objective of this study was to evaluate specific genes as in situ indicators of biological soil response during phytoremediation. The abundance and activity of 16S rRNA, nifH, and amoA were monitored during a nine month phytostabilization study using buffalo grass and quailbush grown in compost-amended, metalliferous tailings. The compost amendment provided a greater than 5-log increase in bacterial abundance, and survival of this compost-inoculum was more stable in planted treatments. Despite increased abundance, the activity of the introduced community was low, and significant increases were not detected until six and nine months in quailbush, and unplanted compost and buffalo grass treatments, respectively. In addition, increased abundances of nitrogen-fixation (nifH) and ammonia-oxidizing (amoA) genes were observed in rhizospheres of buffalo grass and quailbush, respectively. Thus, plant establishment facilitated the short term stabilization of introduced bacterial biomass and supported the growth of two key nitrogen-cycling populations in compost-amended tailings.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Artiola, J., Maier, R. M., & Gandolfi, A. J. (2015). Building a co-created citizen science program with gardeners neighboring a superfund site: The Gardenroots case study. International public health journal, 7(1).
  More info

  A research project that is only expert-driven may ignore the role of local knowledge in research, give low priority to the development of a comprehensive communication strategy to engage the community, and may not deliver the results of the study to the community in an effective way.
• Root, R. A., Hayes, S. M., Hammond, C. M., Maier, R. M., & Chorover, J. (2015). Toxic metal(loid) speciation during weathering of iron sulfide mine tailings under semi-arid climate. Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry, 62, 131-149.
  More info

  Toxic metalliferous mine-tailings pose a significant health risk to ecosystems and neighboring communities from wind and water dispersion of particulates containing high concentrations of toxic metal(loid)s (e.g., Pb, As, Zn). Tailings are particularly vulnerable to erosion before vegetative cover can be reestablished, i.e., decades or longer in semi-arid environments without intervention. Metal(loid) speciation, linked directly to bioaccessibility and lability, is controlled by mineral weathering and is a key consideration when assessing human and environmental health risks associated with mine sites. At the semi-arid Iron King Mine and Humboldt Smelter Superfund site in central Arizona, the mineral assemblage of the top 2 m of tailings has been previously characterized. A distinct redox gradient was observed in the top 0.5 m of the tailings and the mineral assemblage indicates progressive transformation of ferrous iron sulfides to ferrihydrite and gypsum, which, in turn weather to form schwertmannite and then jarosite accompanied by a progressive decrease in pH (7.3 to 2.3). Within the geochemical context of this reaction front, we examined enriched toxic metal(loid)s As, Pb, and Zn with surficial concentrations 41.1, 10.7, 39.3 mM kg(-1) (3080, 2200, and 2570 mg kg(-1)), respectively. The highest bulk concentrations of As and Zn occur at the redox boundary representing a 1.7 and 4.2 fold enrichment relative to surficial concentrations, respectively, indicating the translocation of toxic elements from the gossan zone to either the underlying redox boundary or the surface crust. Metal speciation was also examined as a function of depth using X-ray absorption spectroscopy (XAS). The deepest sample (180 cm) contains sulfides (e.g., pyrite, arsenopyrite, galena, and sphalerite). Samples from the redox transition zone (25-54 cm) contain a mixture of sulfides, carbonates (siderite, ankerite, cerrusite, and smithsonite) and metal(loid)s sorbed to neoformed secondary Fe phases, principally ferrihydrite. In surface samples (0-35 cm), metal(loid)s are found as sorbed species or incorporated into secondary Fe hydroxysulfate phases, such as schwertmannite and jarosites. Metal-bearing efflorescent salts (e.g., ZnSO4·nH2O) were detected in the surficial sample. Taken together, these data suggest the bioaccessibility and lability of metal(loid)s are altered by mineral weathering, which results in both the downward migration of metal(loid)s to the redox boundary, as well as the precipitation of metal salts at the surface.
• Vaughan, M. J., Nelson, W., Soderlund, C., Maier, R. M., & Pryor, B. M. (2015). Assessing fungal community structure from mineral surfaces in Kartchner Caverns using multiplexed 454 pyrosequencing. Microbial ecology, 70(1), 175-87.
  More info

  Research on the distribution and structure of fungal communities in caves is lacking. Kartchner Caverns is a wet and mineralogically diverse carbonate cave located in an escarpment of Mississippian Escabrosa limestone in the Whetstone Mountains, Arizona, USA. Fungal diversity from speleothem and rock wall surfaces was examined with 454 FLX Titanium sequencing technology using the Internal Transcribed Spacer 1 as a fungal barcode marker. Fungal diversity was estimated and compared between speleothem and rock wall surfaces, and its variation with distance from the natural entrance of the cave was quantified. Effects of environmental factors and nutrient concentrations in speleothem drip water at different sample sites on fungal diversity were also examined. Sequencing revealed 2,219 fungal operational taxonomic units (OTUs) at the 95% similarity level. Speleothems supported a higher fungal richness and diversity than rock walls. However, community membership and the taxonomic distribution of fungal OTUs at the class level did not differ significantly between speleothems and rock walls. Both OTU richness and diversity decreased significantly with increasing distance from the natural cave entrance. Community membership and taxonomic distribution of fungal OTUs also differed significantly between the sampling sites closest to the entrance and those furthest away. There was no significant effect of temperature, CO2 concentration, or drip water nutrient concentration on fungal community structure on either speleothems or rock walls. Together, these results suggest that proximity to the natural entrance is a critical factor in determining fungal community structure on mineral surfaces in Kartchner Caverns.
• Artiola, J. F., Brusseau, M. L., Maier, R. M., Ramirez-Andreotta, M., & Gandolfi, J. (2014). Building a Co-CreatedCitizen Science Program with Gardeners Neighboring a Superfund Site: The Gardenroots Case Study. International Public Health Journal, 6(3).
• Chorover, J. D., Maier, R. M., Root, R. A., Hayes, S. M., & Perdrial, N. (2014). Surficial weathering of iron sulfide mine tailings under semi-arid climate. Geochim. Cosmochim. Acta, 141, 240-257.
• Chorover, J. D., Valentin-Vargas, A., Root, R. A., Neilson, J. W., & Maier, R. M. (2014). Environmental factors influencing the structural dynamics of soil microbial communities during assisted phytostabilization of acid-generating mine tailings: A mesocosm experiment.. Sci. Tot. Environ., 500, 314-324.
• Hayes, S. M., Root, R. A., Perdrial, N., Maier, R. M., & Chorover, J. (2014). Surficial weathering of iron sulfide mine tailings under semi-arid climate. GEOCHIMICA ET COSMOCHIMICA ACTA, 141, 240-257.
  More info

  Mine wastes introduce anthropogenic weathering profiles to the critical zone that often remain unvegetated for decades after mining cessation. As such, they are vulnerable to wind and water dispersion of particulate matter to adjacent ecosystems and residential communities. In sulfide-rich ore tailings, propagation to depth of the oxidative weathering front controls the depth-variation in speciation of major and trace elements. Despite the prevalence of surficial mine waste deposits in arid regions of the globe, few prior studies have been conducted to resolve the near-surface profile of sulfide ore tailings weathered under semi-arid climate. We investigated relations between gossan oxidative reaction-front propagation and the molecular speciation of iron and sulfur in tailings subjected to weathering in a semi-arid climate at an EPA Superfund Site in central Arizona (USA). Here we report a multi-method data set combining wet chemical and synchrotron-based X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES) methods to resolve the tight coupling of iron (Fe) and sulfur (S) geochemical changes in the top 2 m of tailings. Despite nearly invariant Fe and S concentration with depth (130-140 and 100-120 g kg(-1), respectively), a sharp redox gradient and distinct morphological change was observed within the top 0.5 m, associated with a progressive oxidative alteration of ferrous sulfides to (oxyhydr)oxides and (hydroxy)sulfates. Transformation is nearly complete in surficial samples. Trends in molecular-scale alteration were co-located with a decrease in pH from 7.3 to 2.3, and shifts in Fe and S lability as measured via chemical extraction. Initial weathering products, ferrihydrite and gypsum, transform to schwertmannite, then jarosite-group minerals with an accompanying decrease in pH. Interestingly, thermodynamically stable phases such as goethite and hematite were not detected in any samples, but ferrihydrite was observed even in samples with the lowest pH, indicating its metastable persistence in these semiarid tailings. The resulting sharp geochemical speciation gradients in close proximity to the tailings surface have important implications for plant colonization, as well as mobility and bioavailability of co-associated toxic metal(loid)s. (C) 2014 Elsevier Ltd. All rights reserved.
• Maier, R. M., Diaz-Barriga, F., Field, J. A., Hopkins, J. C., Klein, B., & Poulton, M. M. (2014). Socially responsible mining: the relationship between mining and poverty, human health and the environment. Reviews on Environmental Health, 29, 83-89.
• Maier, R. M., Díaz-Barriga, F., Field, J. A., Hopkins, J., Klein, B., & Poulton, M. M. (2014). Socially responsible mining: the relationship between mining and poverty, human health and the environment. Reviews on environmental health, 29(1-2), 83-9.
  More info

  Increasing global demand for metals is putting strain on the ability of the mining industry to physically keep up with demand (physical scarcity). Conversely, social issues including the environmental and human health consequences of mining as well as the disparity in income distribution from mining revenues are disproportionately felt at the local community level. This has created social rifts, particularly in the developing world, between affected communities and both industry and governments. Such rifts can result in a disruption of the steady supply of metals (situational scarcity). Here we discuss the importance of mining in relationship to poverty, identify steps that have been taken to create a framework for socially responsible mining, and then discuss the need for academia to work in partnership with communities, government, and industry to develop transdisciplinary research-based step change solutions to the intertwined problems of physical and situational scarcity.
• Ortiz, M., Legatzki, A., Neilson, J. W., Fryslie, B., Nelson, W. M., Wing, R. A., Soderlund, C. A., Pryor, B. M., & Maier, R. M. (2014). Making a living while starving in the dark: metagenomic insights into the energy dynamics of a carbonate cave. ISME JOURNAL, 8(2), 478-491.
  More info

  Carbonate caves represent subterranean ecosystems that are largely devoid of phototrophic primary production. In semiarid and arid regions, allochthonous organic carbon inputs entering caves with vadose-zone drip water are minimal, creating highly oligotrophic conditions; however, past research indicates that carbonate speleothem surfaces in these caves support diverse, predominantly heterotrophic prokaryotic communities. The current study applied a metagenomic approach to elucidate the community structure and potential energy dynamics of microbial communities, colonizing speleothem surfaces in Kartchner Caverns, a carbonate cave in semiarid, southeastern Arizona, USA. Manual inspection of a speleothem metagenome revealed a community genetically adapted to low-nutrient conditions with indications that a nitrogen-based primary production strategy is probable, including contributions from both Archaea and Bacteria. Genes for all six known CO2-fixation pathways were detected in the metagenome and RuBisCo genes representative of the Calvin-Benson-Bassham cycle were over-represented in Kartchner speleothem metagenomes relative to bulk soil, rhizosphere soil and deep-ocean communities. Intriguingly, quantitative PCR found Archaea to be significantly more abundant in the cave communities than in soils above the cave. MEtaGenome ANalyzer (MEGAN) analysis of speleothem metagenome sequence reads found Thaumarchaeota to be the third most abundant phylum in the community, and identified taxonomic associations to this phylum for indicator genes representative of multiple CO2-fixation pathways. The results revealed that this oligotrophic subterranean environment supports a unique chemoautotrophic microbial community with potentially novel nutrient cycling strategies. These strategies may provide key insights into other ecosystems dominated by oligotrophy, including aphotic subsurface soils or aquifers and photic systems such as arid deserts.
• Ortiz, M., Legatzki, A., Neilson, J. W., Fryslie, B., Nelson, W. M., Wing, R. A., Soderlund, C. A., Pryor, B. M., & Maier, R. M. (2014). Making a living while starving in the dark: metagenomic insights into the energy dynamics of a carbonate cave. The ISME journal, 8(2), 478-91.
  More info

  Carbonate caves represent subterranean ecosystems that are largely devoid of phototrophic primary production. In semiarid and arid regions, allochthonous organic carbon inputs entering caves with vadose-zone drip water are minimal, creating highly oligotrophic conditions; however, past research indicates that carbonate speleothem surfaces in these caves support diverse, predominantly heterotrophic prokaryotic communities. The current study applied a metagenomic approach to elucidate the community structure and potential energy dynamics of microbial communities, colonizing speleothem surfaces in Kartchner Caverns, a carbonate cave in semiarid, southeastern Arizona, USA. Manual inspection of a speleothem metagenome revealed a community genetically adapted to low-nutrient conditions with indications that a nitrogen-based primary production strategy is probable, including contributions from both Archaea and Bacteria. Genes for all six known CO2-fixation pathways were detected in the metagenome and RuBisCo genes representative of the Calvin-Benson-Bassham cycle were over-represented in Kartchner speleothem metagenomes relative to bulk soil, rhizosphere soil and deep-ocean communities. Intriguingly, quantitative PCR found Archaea to be significantly more abundant in the cave communities than in soils above the cave. MEtaGenome ANalyzer (MEGAN) analysis of speleothem metagenome sequence reads found Thaumarchaeota to be the third most abundant phylum in the community, and identified taxonomic associations to this phylum for indicator genes representative of multiple CO2-fixation pathways. The results revealed that this oligotrophic subterranean environment supports a unique chemoautotrophic microbial community with potentially novel nutrient cycling strategies. These strategies may provide key insights into other ecosystems dominated by oligotrophy, including aphotic subsurface soils or aquifers and photic systems such as arid deserts.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Artiola, J. F., Maier, R. M., & Gandolfi, A. J. (2014). Environmental Research Translation: Enhancing interactions with communities at contaminated sites. SCIENCE OF THE TOTAL ENVIRONMENT, 497-498, 651-664.
  More info

  The characterization and remediation of contaminated sites are complex endeavors fraught with numerous challenges. One particular challenge that is receiving increased attention is the development and encouragement of full participation by communities and community members affected by a given site in all facets of decision-making. Many disciplines have been grappling with the challenges associated with environmental and risk communication, public participation in environmental data generation, and decision-making and increasing community capacity. The concepts and methods developed by these disciplines are reviewed, with a focus on their relevance to the specific dynamics associated with environmental contamination sites. The contributions of these disciplines are then synthesized and integrated to help develop Environmental Research Translation (ERT), a proposed framework for environmental scientists to promote interaction and communication among involved parties at contaminated sites. This holistic approach is rooted in public participation approaches to science, which includes: a transdisciplinary team, effective collaboration, information transfer, public participation in environmental projects, and a cultural model of risk communication. Although there are challenges associated with the implementation of ERT, it is anticipated that application of this proposed translational science method could promote more robust community participation at contaminated sites. (C) 2014 Elsevier B.V. All rights reserved.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Artiola, J. F., Maier, R. M., & Gandolfi, A. J. (2014). Environmental Research Translation: enhancing interactions with communities at contaminated sites. The Science of the total environment, 497-498, 651-64.
  More info

  The characterization and remediation of contaminated sites are complex endeavors fraught with numerous challenges. One particular challenge that is receiving increased attention is the development and encouragement of full participation by communities and community members affected by a given site in all facets of decision-making. Many disciplines have been grappling with the challenges associated with environmental and risk communication, public participation in environmental data generation, and decision-making and increasing community capacity. The concepts and methods developed by these disciplines are reviewed, with a focus on their relevance to the specific dynamics associated with environmental contamination sites. The contributions of these disciplines are then synthesized and integrated to help develop Environmental Research Translation (ERT), a proposed framework for environmental scientists to promote interaction and communication among involved parties at contaminated sites. This holistic approach is rooted in public participation approaches to science, which includes: a transdisciplinary team, effective collaboration, information transfer, public participation in environmental projects, and a cultural model of risk communication. Although there are challenges associated with the implementation of ERT, it is anticipated that application of this proposed translational science method could promote more robust community participation at contaminated sites.
• Valentin-Vargas, A., Root, R. A., Neilson, J. W., Chorover, J., & Maier, R. M. (2014). Environmental factors influencing the structural dynamics of soil microbial communities during assisted phytostabilization of acid-generating mine tailings: A mesocosm experiment. SCIENCE OF THE TOTAL ENVIRONMENT, 500, 314-324.
  More info

  Compost-assisted phytostabilization has recently emerged as a robust alternative for reclamation of metalliferous mine tailings. Previous studies suggest that root-associated microbes may be important for facilitating plant establishment on the tailings, yet little is known about the long-term dynamics of microbial communities during reclamation. A mechanistic understanding of microbial community dynamics in tailings ecosystems undergoing remediation is critical because these dynamics profoundly influence both the biogeochemical weathering of tailings and the sustainability of a plant cover. Here we monitor the dynamics of soil microbial communities (i.e. bacteria, fungi, archaea) during a 12-month mesocosm study that included 4 treatments: 2 unplanted controls (unamended and compost-amended tailings) and 2 compost-amended seeded tailings treatments. Bacterial, fungal and archaeal communities responded distinctively to the revegetation process and concurrent changes in environmental conditions and pore water chemistry. Compost addition significantly increased microbial diversity and had an immediate and relatively long-lasting buffering-effect on pH, allowing plants to germinate and thrive during the early stages of the experiment. However, the compost buffering capacity diminished after six months and acidification took over as the major factor affecting plant survival and microbial community structure. Immediate changes in bacterial communities were observed following plant establishment, whereas fungal communities showed a delayed response that apparently correlated with the pH decline. Fluctuations in cobalt pore water concentrations, in particular, had a significant effect on the structure of all three microbial groups, which may be linked to the role of cobalt in metal detoxification pathways. The present study represents, to our knowledge, the first documentation of the dynamics of the three major microbial groups during revegetation of compost-amended, metalliferous mine tailings. (C) 2014 Elsevier B.V. All rights reserved.
• Valentín-Vargas, A., Root, R. A., Neilson, J. W., Chorover, J., & Maier, R. M. (2014). Environmental factors influencing the structural dynamics of soil microbial communities during assisted phytostabilization of acid-generating mine tailings: a mesocosm experiment. The Science of the total environment, 500-501, 314-24.
  More info

  Compost-assisted phytostabilization has recently emerged as a robust alternative for reclamation of metalliferous mine tailings. Previous studies suggest that root-associated microbes may be important for facilitating plant establishment on the tailings, yet little is known about the long-term dynamics of microbial communities during reclamation. A mechanistic understanding of microbial community dynamics in tailings ecosystems undergoing remediation is critical because these dynamics profoundly influence both the biogeochemical weathering of tailings and the sustainability of a plant cover. Here we monitor the dynamics of soil microbial communities (i.e. bacteria, fungi, archaea) during a 12-month mesocosm study that included 4 treatments: 2 unplanted controls (unamended and compost-amended tailings) and 2 compost-amended seeded tailings treatments. Bacterial, fungal and archaeal communities responded distinctively to the revegetation process and concurrent changes in environmental conditions and pore water chemistry. Compost addition significantly increased microbial diversity and had an immediate and relatively long-lasting buffering-effect on pH, allowing plants to germinate and thrive during the early stages of the experiment. However, the compost buffering capacity diminished after six months and acidification took over as the major factor affecting plant survival and microbial community structure. Immediate changes in bacterial communities were observed following plant establishment, whereas fungal communities showed a delayed response that apparently correlated with the pH decline. Fluctuations in cobalt pore water concentrations, in particular, had a significant effect on the structure of all three microbial groups, which may be linked to the role of cobalt in metal detoxification pathways. The present study represents, to our knowledge, the first documentation of the dynamics of the three major microbial groups during revegetation of compost-amended, metalliferous mine tailings.
• Zhang, L., Pemberton, J. E., & Maier, R. M. (2014). Effect of fatty acid substrate chain length on Pseudomonas aeruginosa ATCC 9027 monorhamnolipid yield and congener distribution. PROCESS BIOCHEMISTRY, 49(6), 989-995.
  More info

  Rhamnolipids are surface-active molecules produced by Pseudornonas aeruginosa as congener mixtures. They are considered "green" alternatives to synthetic surfactants used in industrial, remediation and pharmaceutical applications. Optimizing yield as well as controlling congener distribution are necessary steps for successful commercialization of rhamnolipids. This study used a mixture of glucose and fatty acids of different chain length (C-12-C-22) and saturation (C-18:1 and C-18:2) to produce monorhamnolipids and determine the effect of fatty acid substrates on rhamnolipid yield, percent carbon conversion and congener distribution. Results show that 1% glucose + 0.25% stearic acid (C-18) produced the greatest yield (2.1 g L-1) compared to other glucose-fatty acid combinations (0.8-1.8 g L-1)(.) Various glucose + C-18 ratios were then tested to optimize yield and percent substrate carbon conversion to monorhamnolipid. Results revealed a positive linear correlation between the mass percent of C-18 used and the percent carbon conversion. A mass percent of 67% C-18 was optimal resulting in a 44% carbon conversion and a yield of 13.7 gL(-1) monorhamnolipid. For all fatty acid substrates tested, the RhaCioCio was the most abundant and RhaC(10)C(12:1) was the least abundant of the four major congeners produced. However, the relative amount of RhaC(10)C(8) and RhaC(10)C(12) congeners was dependent on several factors: in general, fatty acid substrates with relatively short chain length (C-12 and C-14), unsaturated fatty acid substrate (c(18:2)), and longer cultivation time resulted in a higher RhaC(10)C(8)/RhaC(10)C(12) ratio. These findings will assist in mass production of monorhamnolipids and controlling the specific congeners produced. (C) 2014 Elsevier Ltd. All rights reserved.
• Henry, H. F., Burken, J. G., Maier, R. M., Newman, L. A., Rock, S., Schnoor, J. L., & Suk, W. A. (2013). Phytotechnologies - Preventing Exposures, Improving Public Health. International Journal of Phytoremediation, 15(9), 889-899.
  More info

  PMID: 23819283;Abstract: Phytotechnologies have potential to reduce the amount or toxicity of deleterious chemicals and agents, and thereby, can reduce human exposures to hazardous substances. As such, phytotechnologies are tools for primary prevention in public health. Recent research demonstrates phytotechnologies can be uniquely tailored for effective exposure prevention in a variety of applications. In addition to exposure prevention, plants can be used as sensors to identify environmental contamination and potential exposures. In this paper, we have presented applications and research developments in a framework to illustrate how phytotechnologies can meet basic public health needs for access to clean water, air, and food. Because communities can often integrate plant-based technologies at minimal cost and with low infrastructure needs, the use of these technologies can be applied broadly to minimize potential contaminant exposure and improve environmental quality. These natural treatment systems also provide valuable ecosystem services to communities and society. In the future, integrating and coordinating phytotechnology activities with public health research will allow technology development focused on prevention of environmental exposures to toxic compounds. Hence, phytotechnologies may provide sustainable solutions to environmental exposure challenges, improving public health and potentially reducing the burden of disease. © 2013 Copyright Taylor and Francis Group, LLC.
• Henry, H. F., Burken, J. G., Maier, R. M., Newman, L. A., Rock, S., Schnoor, J. L., & Suk, W. A. (2013). Phytotechnologies--preventing exposures, improving public health. International journal of phytoremediation, 15(9).
  More info

  Phytotechnologies have potential to reduce the amount or toxicity of deleterious chemicals and agents, and thereby, can reduce human exposures to hazardous substances. As such, phytotechnologies are tools for primary prevention in public health. Recent research demonstrates phytotechnologies can be uniquely tailored for effective exposure prevention in a variety of applications. In addition to exposure prevention, plants can be used as sensors to identify environmental contamination and potential exposures. In this paper, we have presented applications and research developments in a framework to illustrate how phytotechnologies can meet basic public health needs for access to clean water, air, and food. Because communities can often integrate plant-based technologies at minimal cost and with low infrastructure needs, the use of these technologies can be applied broadly to minimize potential contaminant exposure and improve environmental quality. These natural treatment systems also provide valuable ecosystem services to communities and society. In the future, integrating and coordinating phytotechnology activities with public health research will allow technology development focused on prevention of environmental exposures to toxic compounds. Hence, phytotechnologies may provide sustainable solutions to environmental exposure challenges, improving public health and potentially reducing the burden of disease.
• Neilson, J. W., Jordan, F. L., & Maier, R. M. (2013). Analysis of artifacts limiting the use of DGGE for quantitative diversity analysis. J Microbial Methods, 92, 256-263.
• Neilson, J. W., Jordan, F. L., & Maier, R. M. (2013). Analysis of artifacts suggests DGGE should not be used for quantitative diversity analysis. Journal of Microbiological Methods, 92(3), 256-263.
  More info

  PMID: 23313091;PMCID: PMC3957434;Abstract: PCR-denaturing gradient gel electrophoresis (PCR-DGGE) is widely used in microbial ecology for the analysis of comparative community structure. However, artifacts generated during PCR-DGGE of mixed template communities impede the application of this technique to quantitative analysis of community diversity. The objective of the current study was to employ an artificial bacterial community to document and analyze artifacts associated with multiband signatures and preferential template amplification and to highlight their impacts on the use of this technique for quantitative diversity analysis. Six bacterial species (three Betaproteobacteria, two Alphaproteobacteria, and one Firmicutes) were amplified individually and in combinations with primers targeting the V7/V8 region of the 16S rRNA gene. Two of the six isolates produced multiband profiles demonstrating that band number does not correlate directly with α-diversity. Analysis of the multiple bands from one of these isolates confirmed that both bands had identical sequences which lead to the hypothesis that the multiband pattern resulted from two distinct structural conformations of the same amplicon. In addition, consistent preferential amplification was demonstrated following pairwise amplifications of the six isolates. DGGE and real time PCR analysis identified primer mismatch and PCR inhibition due to 16S rDNA secondary structure as the most probable causes of preferential amplification patterns. Reproducible DGGE community profiles generated in this study confirm that PCR-DGGE provides an excellent high-throughput tool for comparative community structure analysis, but that method-specific artifacts preclude its use for accurate comparative diversity analysis. © 2013 Elsevier B.V..
• Ortiz, M., Neilson, J. W., Nelson, W. M., Legatzki, A., Byrne, A., Yeisoo, Y. u., Wing, R. A., Soderlund, C. A., Pryor, B. M., S., L., & Maier, R. M. (2013). Profiling Bacterial Diversity and Taxonomic Composition on Speleothem Surfaces in Kartchner Caverns, AZ. Microbial Ecology, 65(2), 371-383.
  More info

  PMID: 23224253;Abstract: Caves are relatively accessible subterranean habitats ideal for the study of subsurface microbial dynamics and metabolisms under oligotrophic, non-photosynthetic conditions. A 454-pyrotag analysis of the V6 region of the 16S rRNA gene was used to systematically evaluate the bacterial diversity of ten cave surfaces within Kartchner Caverns, a limestone cave. Results showed an average of 1,994 operational taxonomic units (97 % cutoff) per speleothem and a broad taxonomic diversity that included 21 phyla and 12 candidate phyla. Comparative analysis of speleothems within a single room of the cave revealed three distinct bacterial taxonomic profiles dominated by either Actinobacteria, Proteobacteria, or Acidobacteria. A gradient in observed species richness along the sampling transect revealed that the communities with lower diversity corresponded to those dominated by Actinobacteria while the more diverse communities were those dominated by Proteobacteria. A 16S rRNA gene clone library from one of the Actinobacteria-dominated speleothems identified clones with 99 % identity to chemoautotrophs and previously characterized oligotrophs, providing insights into potential energy dynamics supporting these communities. The robust analysis conducted for this study demonstrated a rich bacterial diversity on speleothem surfaces. Further, it was shown that seemingly comparable speleothems supported divergent phylogenetic profiles suggesting that these communities are very sensitive to subtle variations in nutritional inputs and environmental factors typifying speleothem surfaces in Kartchner Caverns. © 2012 Springer Science+Business Media New York.
• Ortiz, M., Neilson, J. W., Nelson, W. M., Legatzki, A., Byrne, A., Yu, Y., Wing, R. A., Soderlund, C. A., Pryor, B. M., Pierson, L. S., & Maier, R. M. (2013). Profiling bacterial diversity and taxonomic composition on speleothem surfaces in Kartchner Caverns, AZ. Microbial ecology, 65(2).
  More info

  Caves are relatively accessible subterranean habitats ideal for the study of subsurface microbial dynamics and metabolisms under oligotrophic, non-photosynthetic conditions. A 454-pyrotag analysis of the V6 region of the 16S rRNA gene was used to systematically evaluate the bacterial diversity of ten cave surfaces within Kartchner Caverns, a limestone cave. Results showed an average of 1,994 operational taxonomic units (97 % cutoff) per speleothem and a broad taxonomic diversity that included 21 phyla and 12 candidate phyla. Comparative analysis of speleothems within a single room of the cave revealed three distinct bacterial taxonomic profiles dominated by either Actinobacteria, Proteobacteria, or Acidobacteria. A gradient in observed species richness along the sampling transect revealed that the communities with lower diversity corresponded to those dominated by Actinobacteria while the more diverse communities were those dominated by Proteobacteria. A 16S rRNA gene clone library from one of the Actinobacteria-dominated speleothems identified clones with 99 % identity to chemoautotrophs and previously characterized oligotrophs, providing insights into potential energy dynamics supporting these communities. The robust analysis conducted for this study demonstrated a rich bacterial diversity on speleothem surfaces. Further, it was shown that seemingly comparable speleothems supported divergent phylogenetic profiles suggesting that these communities are very sensitive to subtle variations in nutritional inputs and environmental factors typifying speleothem surfaces in Kartchner Caverns.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Artiola, J. F., & Maier, R. M. (2013). A greenhouse and field-based study to determine the accumulation of arsenic in common homegrown vegetables grown in mining-affected soils. The Science of the total environment, 443.
  More info

  The uptake of arsenic by plants from contaminated soils presents a health hazard that may affect home gardeners neighboring contaminated environments. A controlled greenhouse study was conducted in parallel with a co-created citizen science program (home garden experiment) to characterize the uptake of arsenic by common homegrown vegetables near the Iron King Mine and Humboldt Smelter Superfund site in southern Arizona. The greenhouse and home garden arsenic soil concentrations varied considerably, ranging from 2.35 to 533 mg kg(-1). In the greenhouse experiment four vegetables were grown in three different soil treatments and in the home garden experiment a total of 63 home garden produce samples were obtained from 19 properties neighboring the site. All vegetables accumulated arsenic in both the greenhouse and home garden experiments, ranging from 0.01 to 23.0 mg kg(-1) dry weight. Bioconcentration factors were determined and show that arsenic uptake decreased in the order: Asteraceae>Brassicaceae>Amaranthaceae>Cucurbitaceae>Liliaceae>Solanaceae>Fabaceae. Certain members of the Asteraceae and Brassicaceae plant families have been previously identified as hyperaccumulator plants, and it can be inferred that members of these families have genetic and physiological capacity to accumulate, translocate, and resist high amounts of metals. Additionally, a significant linear correlation was observed between the amount of arsenic that accumulated in the edible portion of the plant and the arsenic soil concentration for the Asteraceae, Brassicaceae, Amaranthaceae, and Fabaceae families. The results suggest that home gardeners neighboring mining operations or mine tailings with elevated arsenic levels should be made aware that arsenic can accumulate considerably in certain vegetables, and in particular, it is recommended that gardeners limit consumption of vegetables from the Asteraceae and Brassicaceae plant families.
• Ramirez-Andreotta, M. D., Brusseau, M. L., Beamer, P., & Maier, R. M. (2013). Home gardening near a mining site in an arsenic-endemic region of Arizona: assessing arsenic exposure dose and risk via ingestion of home garden vegetables, soils, and water. The Science of the total environment, 454-455.
  More info

  The human-health risk posed by gardening near a legacy mine and smelter in an arsenic-endemic region of Arizona was characterized in this study. Residential soils were used in a greenhouse study to grow common vegetables, and local residents, after training, collected soil, water, and vegetables samples from their home gardens. Concentrations of arsenic measured in water, soil, and vegetable samples were used in conjunction with reported US intake rates to calculate the daily dose, Incremental Excess Lifetime Cancer Risk (IELCR), and Hazard Quotient for arsenic. Relative arsenic intake dose decreased in order: water>garden soils>homegrown vegetables, and on average, each accounted for 77, 16, and 7% of a residential gardener's daily arsenic intake dose. The IELCR ranges for vegetables, garden soils, and water were 10(-8) to 10(-4), 10(-6) to 10(-4), and 10(-5) to 10(-2), respectively. All vegetables (greenhouse and home garden) were grouped by scientific family, and the risk posed decreased as: Asteraceae≫Fabaceae>Amaranthaceae>Liliaceae>Brassicaceae>Solanaceae≫Cucurbitaceae. Correlations observed between concentrations of arsenic in vegetables and soils were used to estimate a maximum allowable level of arsenic in soil to limit the excess cancer risk to 10(-6). The estimated values are 1.56 mg kg(-1), 5.39 mg kg(-1), 11.6 mg kg(-1) and 12.4 mg kg(-1) for the Asteraceae, Brassicaceae, Fabaceae, and Amaranthaceae families, respectively. It is recommended that home gardeners: sample their private wells annually, test their soils prior to gardening, and, if necessary, modify their gardening behavior to reduce incidental soil ingestion. This study highlights the importance of site-specific risk assessment, and the need for species-specific planting guidelines for communities.
• Valentin-Vargas, A., Chorover, J., & Maier, R. M. (2013). A new standard-based polynomial interpolation (SBPln) method to address gel-to-gel variability for the comparison of multiple denaturing gradient gel electrophoresis profile matrices. J. Microbiol. Meth., 92, 173-177.
• Valentín-Vargas, A., Chorover, J., & Maier, R. M. (2013). A New Standard-Based Polynomial Interpolation (SBPIn) method to address gel-to-gel variability for the comparison of multiple denaturing gradient gel electrophoresis profile matrices. Journal of Microbiological Methods, 92(2), 173-177.
  More info

  PMID: 23234884;PMCID: PMC3570647;Abstract: The Standard-Based Polynomial Interpolation (SBPIn) method is a new simple three-step protocol proposed to address common gel-to-gel variations for the comparison of sample profiles across multiple DGGE gels. The advantages of this method include no requirement for additional software or modification of the standard DGGE protocol. © 2012.
• Valentín-Vargas, A., Chorover, J., & Maier, R. M. (2013). A New Standard-Based Polynomial Interpolation (SBPIn) method to address gel-to-gel variability for the comparison of multiple denaturing gradient gel electrophoresis profile matrices. Journal of microbiological methods, 92(2).
  More info

  The Standard-Based Polynomial Interpolation (SBPIn) method is a new simple three-step protocol proposed to address common gel-to-gel variations for the comparison of sample profiles across multiple DGGE gels. The advantages of this method include no requirement for additional software or modification of the standard DGGE protocol.
• de, M., Meza-Figueroa, D., Maier, R. M., Moreno, D., Gómez-Alvarez, A., Río-Salas, R. D., Mendívil, H., & Montijo, A. (2013). Erosive processes in the Presa I mine dam at Nacozari de Garcia, Sonora, and their effect in the dispersion of pollutants. Boletin de la Sociedad Geologica Mexicana, 65(1), 27-38.
  More info

  Abstract: The operation and exploitation of the Pilares breccia-pipe copper ore deposit and its subsequent cessation of activities in 1945 generated approximately 20 million tons in mine tailings and waste, currently covering a 19 hectares surface located within the urbanized area of Nacozari de Garcia, Sonora. The studied mine tailings are unconfined, with unstable slopes of 50°, lack of vegetation and seasonal efflorescent salts haved formed onthe surface. Such characteristics generate high eolian and water erosion and the possiblecollapse of material. In this work, calculated erosion is classified as severe to very severe. Granulometric characteristics of the tailings mark significant differences in theintensity of water erosion. The physical characterization of the tailings shows two areas of different granulometry that influence in the oxidation of sulfides and metal release: an area of large particle size, and another of fine particle size produced by the flotation process. Climate indexes were estimated for a time period from 1960 to 2011. The aridity index of Martonne shows a rank from 47 to 66, varying from humid in thé60s and́70s to perhumid in thé80s, and humid at present. The Lang index shows values from 15.2 to 22.8, which classifies as a steppe. Copper contents in residential soils and airborne dust collected at two meters height exceed the geochemical background.
• Hayes, S. M., Webb, S. M., Bargar, J. R., O'Day, P. A., Maier, R. M., & Chorover, J. (2012). Geochemical weathering increases lead bioaccessibility in semi-arid mine tailings. Environmental Science and Technology, 46(11), 5834-5841.
  More info

  PMID: 22553941;PMCID: PMC3376710;Abstract: Mine tailings can host elevated concentrations of toxic metal(loid)s that represent a significant hazard to surrounding communities and ecosystems. Eolian transport, capable of translocating small (micrometer-sized) particles, can be the dominant mechanism of toxic metal dispersion in arid or semiarid landscapes. Human exposure to metals can then occur via direct inhalation or ingestion of particulates. The fact that measured doses of total lead (Pb) in geomedia correlate poorly with blood Pb levels highlights a need to better resolve the precise distribution of molecularly speciated metal-bearing phases in the complex particle mixtures. Species distribution controls bioaccessibility, thereby directly impacting health risk. This study seeks to correlate Pb-containing particle size and mineral composition with lability and bioaccessibility in mine tailings subjected to weathering in a semiarid environment. We employed X-ray absorption spectroscopy (XAS) and X-ray fluorescence (XRF), coupled with sequential chemical extractions, to study Pb speciation in tailings from the semiarid Arizona Klondyke State Superfund Site. Representative samples ranging in pH from 2.6 to 5.4 were selected for in-depth study of Pb solid-phase speciation. The principle lead-bearing phase was plumbojarosite (PbFe6(SO4)4(OH)12), but anglesite (PbSO4) and iron oxide-sorbed Pb were also observed. Anglesite, the most bioavailable mineral species of lead identified in this study, was enriched in surficial tailings samples, where Pb concentrations in the clay size fraction were 2-3 times higher by mass relative to bulk. A mobile and bioaccessible Pb phase accumulates in surficial tailings, with a corresponding increase in risk of human exposure to atmospheric particles. © 2012 American Chemical Society.
• Hayes, S. M., Webb, S. M., Bargar, J. R., O'Day, P. A., Maier, R. M., & Chorover, J. (2012). Geochemical weathering increases lead bioaccessibility in semi-arid mine tailings. Environmental science & technology, 46(11), 5834-41.
  More info

  Mine tailings can host elevated concentrations of toxic metal(loid)s that represent a significant hazard to surrounding communities and ecosystems. Eolian transport, capable of translocating small (micrometer-sized) particles, can be the dominant mechanism of toxic metal dispersion in arid or semiarid landscapes. Human exposure to metals can then occur via direct inhalation or ingestion of particulates. The fact that measured doses of total lead (Pb) in geomedia correlate poorly with blood Pb levels highlights a need to better resolve the precise distribution of molecularly speciated metal-bearing phases in the complex particle mixtures. Species distribution controls bioaccessibility, thereby directly impacting health risk. This study seeks to correlate Pb-containing particle size and mineral composition with lability and bioaccessibility in mine tailings subjected to weathering in a semiarid environment. We employed X-ray absorption spectroscopy (XAS) and X-ray fluorescence (XRF), coupled with sequential chemical extractions, to study Pb speciation in tailings from the semiarid Arizona Klondyke State Superfund Site. Representative samples ranging in pH from 2.6 to 5.4 were selected for in-depth study of Pb solid-phase speciation. The principle lead-bearing phase was plumbojarosite (PbFe(6)(SO(4))(4)(OH)(12)), but anglesite (PbSO(4)) and iron oxide-sorbed Pb were also observed. Anglesite, the most bioavailable mineral species of lead identified in this study, was enriched in surficial tailings samples, where Pb concentrations in the clay size fraction were 2-3 times higher by mass relative to bulk. A mobile and bioaccessible Pb phase accumulates in surficial tailings, with a corresponding increase in risk of human exposure to atmospheric particles.
• Legatzki, A., Ortiz, M., Neilson, J. W., Casavant, R. R., Palmer, M. W., Rasmussen, C., Pryor, B. M., III, L. P., & Maier, R. M. (2012). Factors Influencing Observed Variations in the Structure of Bacterial Communities On Calcite Formations in Kartchner Caverns, AZ, USA. Geomicrobiology Journal, 29(5), 422-434.
  More info

  Abstract: Kartchner Caverns is an oligotrophic subterranean environment that hosts a wide diversity of actively growing calcite speleothems (secondary mineral deposits). In a previous study, we demonstrated that bacterial communities extracted from these surfaces are quite complex and vary between formations. In the current study, we evaluated the influence of several environmental variables on the superficial bacterial community structure of 10 active formations located in close proximity to one another in a small room of Kartchner Caverns State Park, Arizona, USA. Physical (color, dimensions) and chemical (elemental profile and organic carbon concentration) properties, as well as the DGGE-based bacterial community structure of the formations were analyzed. While elemental concentration was found to vary among the formations, the differences in the community structure could not be correlated with concentrations of either organic carbon or any of the elements evaluated. In contrast, the locations of formations within a distinct region of the cave as well as the relative location of specific formations within a single room were found to have a significant influence on the bacterial community structure of the formations evaluated. Interestingly, Canonical Correspondence Analysis suggests an association between the observed drip pathways (drip lines) feeding the formations (as determined by the patterns of soda straws and small stalactites that reveal water flow patterns) and the bacterial community structure of the respective formations. The results presented here indicate that a broad range of formations fed by a diversity of drip sources must be sampled to fully characterize the community composition of bacteria present on the surfaces of calcite formations in carbonate caves. © 2012 Taylor and Francis Group, LLC.
• Neilson, J. W., Quade, J., Ortiz, M., Nelson, W. M., Legatzki, A., Tian, F., LaComb, M., Betancourt, J. L., Wing, R. A., Soderlund, C. A., & Maier, R. M. (2012). Life at the hyperarid margin: novel bacterial diversity in arid soils of the Atacama Desert, Chile. Extremophiles : life under extreme conditions, 16(3), 553-66.
  More info

  Nearly half the earth's surface is occupied by dryland ecosystems, regions susceptible to reduced states of biological productivity caused by climate fluctuations. Of these regions, arid zones located at the interface between vegetated semiarid regions and biologically unproductive hyperarid zones are considered most vulnerable. The objective of this study was to conduct a deep diversity analysis of bacterial communities in unvegetated arid soils of the Atacama Desert, to characterize community structure and infer the functional potential of these communities based on observed phylogenetic associations. A 454-pyrotag analysis was conducted of three unvegetated arid sites located at the hyperarid-arid margin. The analysis revealed communities with unique bacterial diversity marked by high abundances of novel Actinobacteria and Chloroflexi and low levels of Acidobacteria and Proteobacteria, phyla that are dominant in many biomes. A 16S rRNA gene library of one site revealed the presence of clones with phylogenetic associations to chemoautotrophic taxa able to obtain energy through oxidation of nitrite, carbon monoxide, iron, or sulfur. Thus, soils at the hyperarid margin were found to harbor a wealth of novel bacteria and to support potentially viable communities with phylogenetic associations to non-phototrophic primary producers and bacteria capable of biogeochemical cycling.
• Solís-Dominguez, F. A., White, S. A., Hutter, T. B., Amistadi, M. K., Root, R. A., Chorover, J., & Maier, R. M. (2012). Response of key soil parameters during compost-assisted phytostabilization in extremely acidic tailings: Effect of plant species. Environmental Science and Technology, 46(2), 1019-1027.
  More info

  PMID: 22191663;PMCID: PMC3263829;Abstract: Phytostabilization of mine tailings acts to mitigate both eolian dispersion and water erosion events which can disseminate barren tailings over large distances. This technology uses plants to establish a vegetative cover to permanently immobilize contaminants in the rooting zone, often requiring addition of an amendment to assist plant growth. Here we report the results of a greenhouse study that evaluated the ability of six native plant species to grow in extremely acidic (pH ∼ 2.5) metalliferous (As, Pb, Zn: 2000-3000 mg kg -1) mine tailings from Iron King Mine Humboldt Smelter Superfund site when amended with a range of compost concentrations. Results revealed that three of the six plant species tested (buffalo grass, mesquite, and catclaw acacia) are good candidates for phytostabilization at an optimum level of 15% compost (w/w) amendment showing good growth and minimal shoot accumulation of metal(loid)s. A fourth candidate, quailbush, also met all criteria except for exceeding the domestic animal toxicity limit for shoot accumulation of zinc. A key finding of this study was that the plant species that grew most successfully on these tailings significantly influenced key tailings parameters; direct correlations between plant biomass and both increased tailings pH and neutrophilic heterotrophic bacterial counts were observed. We also observed decreased iron oxidizer counts and decreased bioavailability of metal(loid)s mainly as a result of compost amendment. Taken together, these results suggest that the phytostabilization process reduced tailings toxicity as well as the potential for metal(loid) mobilization. This study provides practical information on plant and tailings characteristics that is critically needed for successful implementation of assisted phytostabilization on acidic, metalliferous mine tailings sites. © 2011 American Chemical Society.
• Solís-Dominguez, F. A., White, S. A., Hutter, T. B., Amistadi, M. K., Root, R. A., Chorover, J., & Maier, R. M. (2012). Response of key soil parameters during compost-assisted phytostabilization in extremely acidic tailings: effect of plant species. Environmental science & technology, 46(2), 1019-27.
  More info

  Phytostabilization of mine tailings acts to mitigate both eolian dispersion and water erosion events which can disseminate barren tailings over large distances. This technology uses plants to establish a vegetative cover to permanently immobilize contaminants in the rooting zone, often requiring addition of an amendment to assist plant growth. Here we report the results of a greenhouse study that evaluated the ability of six native plant species to grow in extremely acidic (pH ∼ 2.5) metalliferous (As, Pb, Zn: 2000-3000 mg kg(-1)) mine tailings from Iron King Mine Humboldt Smelter Superfund site when amended with a range of compost concentrations. Results revealed that three of the six plant species tested (buffalo grass, mesquite, and catclaw acacia) are good candidates for phytostabilization at an optimum level of 15% compost (w/w) amendment showing good growth and minimal shoot accumulation of metal(loid)s. A fourth candidate, quailbush, also met all criteria except for exceeding the domestic animal toxicity limit for shoot accumulation of zinc. A key finding of this study was that the plant species that grew most successfully on these tailings significantly influenced key tailings parameters; direct correlations between plant biomass and both increased tailings pH and neutrophilic heterotrophic bacterial counts were observed. We also observed decreased iron oxidizer counts and decreased bioavailability of metal(loid)s mainly as a result of compost amendment. Taken together, these results suggest that the phytostabilization process reduced tailings toxicity as well as the potential for metal(loid) mobilization. This study provides practical information on plant and tailings characteristics that is critically needed for successful implementation of assisted phytostabilization on acidic, metalliferous mine tailings sites.
• Zhang, L., Veres-Schalnat, T. A., Somogyi, A., Pemberton, J. E., & Maier, R. M. (2012). Fatty acid cosubstrates provide β-oxidation precursors for rhamnolipid biosynthesis in Pseudomonas aeruginosa, as evidenced by isotope tracing and gene expression assays. Applied and environmental microbiology, 78(24), 8611-22.
  More info

  Rhamnolipids have multiple potential applications as "green" surfactants for industry, remediation, and medicine. As a result, they have been intensively investigated to add to our understanding of their biosynthesis and improve yields. Several studies have noted that the addition of a fatty acid cosubstrate increases rhamnolipid yields, but a metabolic explanation has not been offered, partly because biosynthesis studies to date have used sugar or sugar derivatives as the carbon source. The objective of this study was to investigate the role of fatty acid cosubstrates in improving rhamnolipid biosynthesis. A combination of stable isotope tracing and gene expression assays was used to identify lipid precursors and potential lipid metabolic pathways used in rhamnolipid synthesis when fatty acid cosubstrates are present. To this end, we compared the rhamnolipids produced and their yields using either glucose alone or glucose and octadecanoic acid-d(35) as cosubstrates. Using a combination of sugar and fatty acids, the rhamnolipid yield was significantly higher (i.e., doubled) than when glucose was used alone. Two patterns of deuterium incorporation (either 1 or 15 deuterium atoms) in a single Rha-C(10) lipid chain were observed for octadecanoic acid-d(35) treatment, indicating that in the presence of a fatty acid cosubstrate, both de novo fatty acid synthesis and β-oxidation are used to provide lipid precursors for rhamnolipids. Gene expression assays showed a 200- to 600-fold increase in the expression of rhlA and rhlB rhamnolipid biosynthesis genes and a more modest increase of 3- to 4-fold of the fadA β-oxidation pathway gene when octadecanoic acid was present. Taken together, these results suggest that the simultaneous use of de novo fatty acid synthesis and β-oxidation pathways allows for higher production of lipid precursors, resulting in increased rhamnolipid yields.
• Hayes, S. M., O'Day, P. A., Webb, S. M., Maier, R. M., & Chorover, J. (2011). Changes in zinc speciation with mine tailings acidification in a semiarid weathering environment. Environmental Science and Technology, 45(17), 7166-7172.
  More info

  PMID: 21761897;PMCID: PMC3175378;Abstract: High concentrations of residual metal contaminants in mine tailings can be transported easily by wind and water, particularly when tailings remain unvegetated for decades following mining cessation, as is the case in semiarid landscapes. Understanding the speciation and mobility of contaminant metal(loid)s, particularly in surficial tailings, is essential to controlling their phytotoxicities and to revegetating impacted sites. In prior work, we showed that surficial tailings samples from the Klondyke State Superfund Site (AZ, USA), ranging in pH from 5.4 to 2.6, represent a weathering series, with acidification resulting from sulfide mineral oxidation, long-term Fe hydrolysis, and a concurrent decrease in total (6000 to 450 mg kg -1) and plant-available (590 to 75 mg kg -1) Zn due to leaching losses and changes in Zn speciation. Here, we used bulk and microfocused Zn K-edge X-ray absorption spectroscopy (XAS) data and a six-step sequential extraction procedure to determine tailings solid phase Zn speciation. Bulk sample spectra were fit by linear combination using three references: Zn-rich phyllosilicate (Zn 0.8talc), Zn sorbed to ferrihydrite (Zn adsFeOx), and zinc sulfate (ZnSO 4·7H 2O). Analyses indicate that Zn sorbed in tetrahedral coordination to poorly crystalline Fe and Mn (oxyhydr)oxides decreases with acidification in the weathering sequence, whereas octahedral zinc in sulfate minerals and crystalline Fe oxides undergoes a relative accumulation. Microscale analyses identified hetaerolite (ZnMn 2O 4), hemimorphite (Zn 4Si 2O 7(OH) 2·H 2O) and sphalerite (ZnS) as minor phases. Bulk and microfocused spectroscopy complement the chemical extraction results and highlight the importance of using a multimethod approach to interrogate complex tailings systems. © 2011 American Chemical Society.
• Hayes, S. M., O'Day, P. A., Webb, S. M., Maier, R. M., & Chorover, J. (2011). Changes in zinc speciation with mine tailings acidification in a semiarid weathering environment. Environmental science & technology, 45(17), 7166-72.
  More info

  High concentrations of residual metal contaminants in mine tailings can be transported easily by wind and water, particularly when tailings remain unvegetated for decades following mining cessation, as is the case in semiarid landscapes. Understanding the speciation and mobility of contaminant metal(loid)s, particularly in surficial tailings, is essential to controlling their phytotoxicities and to revegetating impacted sites. In prior work, we showed that surficial tailings samples from the Klondyke State Superfund Site (AZ, USA), ranging in pH from 5.4 to 2.6, represent a weathering series, with acidification resulting from sulfide mineral oxidation, long-term Fe hydrolysis, and a concurrent decrease in total (6000 to 450 mg kg(-1)) and plant-available (590 to 75 mg kg(-1)) Zn due to leaching losses and changes in Zn speciation. Here, we used bulk and microfocused Zn K-edge X-ray absorption spectroscopy (XAS) data and a six-step sequential extraction procedure to determine tailings solid phase Zn speciation. Bulk sample spectra were fit by linear combination using three references: Zn-rich phyllosilicate (Zn(0.8)talc), Zn sorbed to ferrihydrite (Zn(adsFeOx)), and zinc sulfate (ZnSO(4) · 7H(2)O). Analyses indicate that Zn sorbed in tetrahedral coordination to poorly crystalline Fe and Mn (oxyhydr)oxides decreases with acidification in the weathering sequence, whereas octahedral zinc in sulfate minerals and crystalline Fe oxides undergoes a relative accumulation. Microscale analyses identified hetaerolite (ZnMn(2)O(4)), hemimorphite (Zn(4)Si(2)O(7)(OH)(2) · H(2)O) and sphalerite (ZnS) as minor phases. Bulk and microfocused spectroscopy complement the chemical extraction results and highlight the importance of using a multimethod approach to interrogate complex tailings systems.
• Legatzki, A., Ortiz, M., Neilson, J. W., Dominguez, S., Andersen, G. L., Toomey, R. S., Pryor, B. M., S., L., & Maier, R. M. (2011). Bacterial and archaeal community structure of two adjacent calcite speleothems in Kartchner Caverns, Arizona, USA. Geomicrobiology Journal, 28(2), 99-117.
  More info

  Abstract: Information concerning the bacterial and archaeal communities present on calcite speleothems in carbonate caves is of interest because the activity of these microbes has been implicated as a potential biogenic component in the formation of secondary mineral deposits. In addition, these speleothems may harbor unique, previously unidentified microbes. The current study presents a comparative analysis of the superficial bacterial and archaeal community structure of multiple stalactites from two different cave formations located in close proximity to each other in a nonhuman-impacted area of Kartchner Caverns, Arizona, USA. PCR-denaturing gradient gel electrophoresis analysis (PCR-DGGE) revealed that microbial communities sampled from stalactites of a single speleothem are more similar to each other than to the communities sampled from stalactites of an adjacent speleothem, suggesting that both bacterial and archaeal communities are speleothem-specific. SR-XRD analysis confirmed that both speleothems sampled were primarily calcite, but subtle differences were detected in the elemental composition profiles obtained from ICP-MS analysis indicating that substrate geochemistry was also speleothem-specific. PhyloChip analysis of composite samples from both speleothems revealed a broad diversity of phyla represented in the bacterial communities, while bacterial and archaeal bands sequenced from the DGGE profiles confirmed the presence of unique phylotypes not closely related (< 96% similarity) to any sequences deposited in the GenBank database. © Taylor & Francis Group, LLC.
• Solís-Domínguez, F. A., Valentín-Vargas, A., Chorover, J., & Maier, R. M. (2011). Effect of arbuscular mycorrhizal fungi on plant biomass and the rhizosphere microbial community structure of mesquite grown in acidic lead/zinc mine tailings. Science of the Total Environment, 409(6), 1009-1016.
  More info

  PMID: 21211826;PMCID: PMC3030643;Abstract: Mine tailings in arid and semi-arid environments are barren of vegetation and subject to eolian dispersion and water erosion. Revegetation is a cost-effective strategy to reduce erosion processes and has wide public acceptance. A major cost of revegetation is the addition of amendments, such as compost, to allow plant establishment. In this paper we explore whether arbuscular mycorrhizal fungi (AMF) can help support plant growth in tailings at a reduced compost concentration. A greenhouse experiment was performed to determine the effects of three AMF inocula on biomass, shoot accumulation of heavy metals, and changes in the rhizosphere microbial community structure of the native plant Prosopis juliflora (mesquite). Plants were grown in an acidic lead/zinc mine tailings amended with 10% (w/w) compost amendment, which is slightly sub-optimal for plant growth in these tailings. After two months, AMF-inoculated plants showed increased dry biomass and root length (p< 0.05) and effective AMF colonization compared to controls grown in uninoculated compost-amended tailings. Mesquite shoot tissue lead and zinc concentrations did not exceed domestic animal toxicity limits regardless of whether AMF inoculation was used. The rhizosphere microbial community structure was assessed using denaturing gradient gel electrophoresis (DGGE) profiles of the small subunit RNA gene for bacteria and fungi. Canonical correspondence analysis (CCA) of DGGE profiles showed that the rhizosphere fungal community structure at the end of the experiment was significantly different from the community structure in the tailings, compost, and AMF inocula prior to planting. Further, CCA showed that AMF inoculation significantly influenced the development of both the fungal and bacterial rhizosphere community structures after two months. The changes observed in the rhizosphere microbial community structure may be either a direct effect of the AMF inocula, caused by changes in plant physiology induced by AMF, or a combination of both mechanisms. © 2010 Elsevier B.V.
• Solís-Domínguez, F. A., Valentín-Vargas, A., Chorover, J., & Maier, R. M. (2011). Effect of arbuscular mycorrhizal fungi on plant biomass and the rhizosphere microbial community structure of mesquite grown in acidic lead/zinc mine tailings. The Science of the total environment, 409(6), 1009-16.
  More info

  Mine tailings in arid and semi-arid environments are barren of vegetation and subject to eolian dispersion and water erosion. Revegetation is a cost-effective strategy to reduce erosion processes and has wide public acceptance. A major cost of revegetation is the addition of amendments, such as compost, to allow plant establishment. In this paper we explore whether arbuscular mycorrhizal fungi (AMF) can help support plant growth in tailings at a reduced compost concentration. A greenhouse experiment was performed to determine the effects of three AMF inocula on biomass, shoot accumulation of heavy metals, and changes in the rhizosphere microbial community structure of the native plant Prosopis juliflora (mesquite). Plants were grown in an acidic lead/zinc mine tailings amended with 10% (w/w) compost amendment, which is slightly sub-optimal for plant growth in these tailings. After two months, AMF-inoculated plants showed increased dry biomass and root length (p
• Vaughan, M. J., Maier, R. M., & Pryor, B. M. (2011). Fungal communities on speleothem surfaces in Kartchner caverns, Arizona, USA. International Journal of Speleology, 40(1), 65-77.
  More info

  Abstract: Kartchner Caverns, located near Benson, Arizona, USA, is an active carbonate cave that serves as the major attraction for Kartchner Caverns State Park. Low-impact development and maintenance have preserved prediscovery macroscopic cavern features and minimized disturbances to biological communities within the cave. The goal of this study was to examine fungal diversity in Kartchner Caverns on actively-forming speleothem surfaces. Fifteen formations were sampled from fve sites across the cave. Richness was assessed using standard culture-based fungal isolation techniques. A culture-independent analysis using denaturing gradient gel electrophoresis (DGGE) was used to assay evidence of community homogeneity across the cave through the separation of 18S rDNA amplicons from speleothem community DNA. The culturing effort recovered 53 distinct morphological taxonomic units (MTUs), corresponding to 43 genetic taxonomic units (GTUs) that represented 21 genera. From the observed MTU accumulation curve and the projected total MTU richness curve, it is estimated that 51 percent of the actual MTU richness was recovered. The most commonly isolated fungi belonged to the genera Penicillium, Paecilomyces, Phialophora, and Aspergillus. This culture-based analysis did not reveal signifcant differences in fungal richness or number of fungi recovered across sites. Cluster analysis using DGGE band profles did not reveal distinctive groupings of speleothems by sample site. However, canonical correspondence analysis (CCA) of culture-independent DGGE profles showed a signifcant effect of sampling site and formation type on fungal community structure. Taken together, these results reveal that diverse fungal communities exist on speleothem surfaces in Kartchner Caverns, and that these communities are not uniformly distributed spatially. Analysis of sample saturation indicated that more sampling depth is required to uncover the full scale of mycological richness across spelothem surfaces.
• Wickramasekara, S., Neilson, J., Patel, N., Breci, L., Hilderbrand, A., Maier, R. M., & Wysocki, V. (2011). Proteomics analyses of the opportunistic pathogen Burkholderia vietnamiensis using protein fractionations and mass spectrometry. Journal of Biomedicine and Biotechnology, 2011.
  More info

  PMID: 22187530;PMCID: PMC3237022;Abstract: The main objectives of this work were to obtain a more extensive coverage of the Burkholderia vietnamiensis proteome than previously reported and to identify virulence factors using tandem mass spectrometry. The proteome of B. vietnamiensis was precipitated into four fractions to as extracellular, intracellular, cell surface and cell wall proteins. Two different approaches were used to analyze the proteins. The first was a gel-based method where 1D SDS-PAGE was used for separation of the proteins prior to reverse phase liquid chromatography tandem mass spectrometry (LC-MS/MS). The second method used MudPIT analysis (Multi dimensional Protein Identification Technique), where proteins are digested and separated using cation exchange and reversed phase separations before the MS/MS analysis (LC/LC-MS/MS). Overall, gel-based LC-MS/MS analysis resulted in more protein identifications than the MudPIT analysis. Combination of the results lead to identification of more than 1200 proteins, approximately 16 of the proteins coded from the annotated genome of Burkholderia species. Several virulence factors were detected including flagellin, porin, peroxiredoxin and zinc proteases. © 2011 Samanthi Wickramasekara et al.
• Wickramasekara, S., Neilson, J., Patel, N., Breci, L., Hilderbrand, A., Maier, R. M., & Wysocki, V. (2011). Proteomics analyses of the opportunistic pathogen Burkholderia vietnamiensis using protein fractionations and mass spectrometry. Journal of biomedicine & biotechnology, 2011, 701928.
  More info

  The main objectives of this work were to obtain a more extensive coverage of the Burkholderia vietnamiensis proteome than previously reported and to identify virulence factors using tandem mass spectrometry. The proteome of B. vietnamiensis was precipitated into four fractions to as extracellular, intracellular, cell surface and cell wall proteins. Two different approaches were used to analyze the proteins. The first was a gel-based method where 1D SDS-PAGE was used for separation of the proteins prior to reverse phase liquid chromatography tandem mass spectrometry (LC-MS/MS). The second method used MudPIT analysis (Multi dimensional Protein Identification Technique), where proteins are digested and separated using cation exchange and reversed phase separations before the MS/MS analysis (LC/LC-MS/MS). Overall, gel-based LC-MS/MS analysis resulted in more protein identifications than the MudPIT analysis. Combination of the results lead to identification of more than 1200 proteins, approximately 16% of the proteins coded from the annotated genome of Burkholderia species. Several virulence factors were detected including flagellin, porin, peroxiredoxin and zinc proteases.
• Ahad, S. M., Ange, A. L., Bates, R. B., Bell, B. L., Bodour, A. A., Bourne, B. R., Contreras, C. G., Goldberg, E. L., Gunatilaka, A. L., King, S., Lee, A. K., Low, R. L., Maier, R. M., Marlor, K. M., Marron, M. T., Scolnik, R. C., Streeter, M. J., Strelczuk, M., Trinh, L. N., , Truong, V. K., et al. (2010). Synthesis and biological activities of flavolipids. Tetrahedron, 66(47), 9107-9112.
  More info

  Abstract: Syntheses of the bacterial surfactants 6S,6S-, 9S,9S-, and 9U,9U-flavolipids confirmed the structures proposed for them from spectroscopic analysis of a flavolipid mixture and made pure flavolipids available for the first time. All three synthetic flavolipids and a straight chain analogue were found to be weakly cytotoxic and to inhibit metastatic cancer cell migration, with 9U,9U-flavolipid (the most abundant natural flavolipid) having the most activity. Biosynthetic routes to the branched side-chains of the flavolipids are suggested, and it is proposed that branched chains are employed to hinder biodegradation. © 2010 Elsevier Ltd. All rights reserved.
• Baughman, K. F., Maier, R. M., Norris, T. A., Beam, B. M., Mudalige, A., Pemberton, J. E., & Curry, J. E. (2010). Evaporative deposition patterns of bacteria from a sessile drop: effect of changes in surface wettability due to exposure to a laboratory atmosphere. Langmuir : the ACS journal of surfaces and colloids, 26(10), 7293-8.
  More info

  Evaporative deposition from a sessile drop is a simple and appealing way to deposit materials on a surface. In this work, we deposit living, motile colloidal particles (bacteria) on mica from drops of aqueous solution. We show for the first time that it is possible to produce a continuous variation in the deposition pattern from ring deposits to cellular pattern deposits by incremental changes in surface wettability which we achieve by timed exposure of the mica surface to the atmosphere. We show that it is possible to change the contact angle of the drop from less than 5 degrees to near 20 degrees by choice of atmospheric exposure time. This controls the extent of drop spreading, which in turn determines the architecture of the deposition pattern.
• Baughman, K., Maier, R. M., & Curry, J. E. (2010). Evaporative deposition of bacteria from a sessile drop: Effects of suspension aging. Materials Research Society Symposium Proceedings, 1273, 25-30.
  More info

  Abstract: In this work, we report on the evaporative deposition of bacteria from a drying aqueous drop on mica as a function of the bacterial suspension age. For sufficiently aged bacterial suspensions, residues are small and more filled-in than residues formed from fresh suspensions on similarly aged mica. In addition, the interior deposition pattern transitions from a cellular film characteristic of fresh suspensions to a cracked carpet pattern for aged suspensions. Suspension aging related changes in the residues are attributed to accumulation of organic materials such as DNA, RNA, proteins, and other bacterial components in the suspension. The aging process is also observed to be at least partially dependent on ventilation of the suspension during aging. © 2010 Materials Research Society.
• Curry, J. E., Maier, R. M., Norris, T. A., & Baughman, K. (2010). Evaporative deposition of bacteria and microspheres on mica from a sessile drop: The use of surface conditioning in a laboratory atmosphere to control drop spreading and particle deposition patterns. Materials Research Society Symposium Proceedings, 1273, 1-6.
  More info

  Abstract: Evaporative deposition from a sessile drop is an appealing way to deposit materials on a surface due to the simplicity of the technique. In this work we deposit aqueous solutions of two types of colloidal particles, namely bacteria and microspheres, on mica. We show that by controlling the extent of initial drop spreading through subtle changes in surface conditioning caused by exposure to the laboratory atmosphere in a laminar flow hood it is possible to systematically vary the particle deposition patterns. On freshly cleaved mica the contact angle of water is < 5°. Drops of bacterial and microsphere solutions deposited on freshly cleaved mica spread to cover a large surface area. Drying occurs through pinning and depinning events leaving a series of colloidal particle rings. We found in our laboratory that the contact angle of water on mica exposed to a constant flow of filtered laboratory air in a laminar flow hood gradually increases with time. For drops of both bacterial and microsphere solutions there is a corresponding decrease in the extent of drop spreading with increasing exposure of the mica surface to laboratory air. This results in a profound change in the colloidal particle deposition pattern. Short exposures of minutes to hours are enough to decrease spreading and affect the resulting deposition pattern. For our longest mica surface exposure times (months to 1 year) the contact angle of water reaches values near 20°. Spreading of the bacterial and microsphere drops is substantially decreased. A portion of the colloidal particles are deposited in an outer deposition ring which marks the extent of drop spreading and the remainder of the particles are deposited in the drop interior as a honeycomb or cellular film. The fraction of the drop residue covered with the cellular film increases with particle concentration as well as the length of time the mica is exposed to the laboratory atmosphere. This work shows that evaporative deposition on mica is very sensitive to surface conditioning through atmospheric exposure and also suggests that particle deposition patterns can be tuned by small changes in drop spreading. © 2010 Materials Research Society.
• Maier, R. M., Palmer, M. W., Andersen, G. L., Halonen, M. J., Josephson, K. C., Maier, R. S., Martinez, F. D., Neilson, J. W., Stern, D. A., Vercelli, D., & Wright, A. L. (2010). Environmental determinants of and impact on childhood asthma by the bacterial community in household dust. Applied and Environmental Microbiology, 76(8), 2663-2667.
  More info

  PMID: 20154107;PMCID: PMC2849212;Abstract: Asthma increased dramatically in the last decades of the 20th century and is representative of chronic diseases that have been linked to altered microbial exposure and immune responses. Here we evaluate the effects of environmental exposures typically associated with asthma protection or risk on the microbial community structure of household dust (dogs, cats, and day care). PCR-denaturing gradient gel analysis (PCR-DGGE) demonstrated that the bacterial community structure in house dust is significantly impacted by the presence of dogs or cats in the home (P = 0.0190 and 0.0029, respectively) and by whether or not children attend day care (P = 0.0037). In addition, significant differences in the dust bacterial community were associated with asthma outcomes in young children, including wheezing (P = 0.0103) and specific IgE (P = 0.0184). Our findings suggest that specific bacterial populations within the community are associated with either risk or protection from asthma. Copyright © 2010, American Society for Microbiology. All Rights Reserved.
• Maier, R. M., Palmer, M. W., Andersen, G. L., Halonen, M. J., Josephson, K. C., Maier, R. S., Martinez, F. D., Neilson, J. W., Stern, D. A., Vercelli, D., & Wright, A. L. (2010). Environmental determinants of and impact on childhood asthma by the bacterial community in household dust. Applied and environmental microbiology, 76(8), 2663-7.
  More info

  Asthma increased dramatically in the last decades of the 20th century and is representative of chronic diseases that have been linked to altered microbial exposure and immune responses. Here we evaluate the effects of environmental exposures typically associated with asthma protection or risk on the microbial community structure of household dust (dogs, cats, and day care). PCR-denaturing gradient gel analysis (PCR-DGGE) demonstrated that the bacterial community structure in house dust is significantly impacted by the presence of dogs or cats in the home (P = 0.0190 and 0.0029, respectively) and by whether or not children attend day care (P = 0.0037). In addition, significant differences in the dust bacterial community were associated with asthma outcomes in young children, including wheezing (P = 0.0103) and specific IgE (P = 0.0184). Our findings suggest that specific bacterial populations within the community are associated with either risk or protection from asthma.
• Neilson, J. W., Zhang, L., Veres-Schalnat, T. A., Chandler, K. B., Neilson, C. H., Crispin, J. D., Pemberton, J. E., & Maier, R. M. (2010). Cadmium effects on transcriptional expression of rhlB/rhlC genes and congener distribution of monorhamnolipid and dirhamnolipid in Pseudomonas aeruginosa IGB83. Applied microbiology and biotechnology, 88(4), 953-63.
  More info

  While variable production of the biosurfactant, rhamnolipid, by Pseudomonas aeruginosa has been shown to be dependent on growth conditions, no research has evaluated potential relationships between rhamnolipid production and the presence of heavy metals. The current investigation evaluates the influence of Cd(2+) on rhamnolipid synthesis. Cultures grown in the presence of 0.45 and 0.89 mM Cd(2+) were monitored for rhlB/rhlC expression, rhamnolipid yield, and the ratio of monorhamnolipid (RL1) and dirhamnolipid (RL2) produced. Results show a Cd-induced enhancement of rhlB expression in mid-stationary phase (53 h). In addition, sustained production of rhamnolipid through late stationary growth phase (96 h) was observed for Cd-amended cultures, unlike Cd-free control cultures that ceased rhamnolipid production by mid-stationary growth phase. Most significant was an observed increase in the ratio of RL2 to RL1 congeners produced by cultures grown in the presence of Cd(2+). Previous results have shown that the complexation constant for RL2-Cd is several orders of magnitude larger than that of RL1-Cd thus the preferential production of RL2 in the presence of Cd(2+) impacts its bioavailability and toxicity both for the cell and in the surrounding environment.
• de-Bashan, L. E., Hernandez, J. P., Nelson, K. N., Bashan, Y., & Maier, R. M. (2010). Growth of quailbush in acidic, metalliferous desert mine tailings: effect of Azospirillum brasilense Sp6 on biomass production and rhizosphere community structure. Microbial ecology, 60(4), 915-27.
  More info

  Mine tailing deposits in semiarid and arid environments frequently remain devoid of vegetation due to the toxicity of the substrate and the absence of a diverse soil microbial community capable of supporting seed germination and plant growth. The contribution of the plant growth promoting bacterium (PGPB) Azospirillum brasilense Sp6 to the growth of quailbush in compost-amended, moderately acidic, high-metal content mine tailings using an irrigation-based reclamation strategy was examined along with its influence on the rhizosphere bacterial community. Sp6 inoculation resulted in a significant (2.2-fold) increase in plant biomass production. The data suggest that the inoculum successfully colonized the root surface and persisted throughout the 60-day experiment in both the rhizosphere, as demonstrated by excision and sequencing of the appropriate denaturing gradient gel electrophoresis (DGGE) band, and the rhizoplane, as indicated by fluorescent in situ hybridization of root surfaces. Changes in rhizosphere community structure in response to Sp6 inoculation were evaluated after 15, 30, and 60 days using DGGE analysis of 16S rRNA polymerase chain reaction amplicons. A comparison of DGGE profiles using canonical correspondence analysis revealed a significant treatment effect (Sp6-inoculated vs. uninoculated plants vs. unplanted) on bacterial community structure at 15, 30, and 60 days (p 
• de-Bashan, L. E., Hernandez, J., Bashan, Y., & Maier, R. M. (2010). Bacillus pumilus ES4: Candidate plant growth-promoting bacterium to enhance establishment of plants in mine tailings. Environmental and Experimental Botany, 69(3), 343-352.
  More info

  Abstract: Three plant growth-promoting bacteria (PGPB; Bacillus pumilus ES4, B. pumilus RIZO1, and Azospirillum brasilense Cd) were tested for their ability to enhance plant growth and development of the native Sonoran Desert shrub quailbush (Atriplex lentiformis) and for their effect on the native bacterial community in moderately acidic, high-metal content tailings (AHMT) and in neutral, low-metal content natural tailings (NLMT) in controlled greenhouse experiments. Inoculation of quailbush with all three PGPB significantly enhanced plant growth parameters, such as germination, root length, dry weight of shoots and roots, and root/shoot ratio in both types of tailings. The effect of inoculation on the indigenous bacterial community by the most successful PGPB B. pumilus ES4 was evaluated by denaturating gradient gel electrophoresis (PCR-DGGE) fingerprinting and root colonization was followed by specific fluorescent in situ hybridization (FISH). Inoculation with this strain significantly changed the bacterial community over a period of 60 days. FISH analysis showed that the preferred site of colonization was the root tips and root elongation area. This study shows that inoculation of native perennial plants with PGPB can be used for developing technologies for phytostabilizing mine tailings. © 2010 Elsevier B.V.
• de-Bashan, L. E., Hernandez, J., Nelson, K. N., Bashan, Y., & Maier, R. M. (2010). Growth of Quailbush in Acidic, Metalliferous Desert Mine Tailings: Effect of Azospirillum brasilense Sp6 on Biomass Production and Rhizosphere Community Structure. Microbial Ecology, 60(4), 915-927.
  More info

  PMID: 20632001;PMCID: PMC2974781;Abstract: Mine tailing deposits in semiarid and arid environments frequently remain devoid of vegetation due to the toxicity of the substrate and the absence of a diverse soil microbial community capable of supporting seed germination and plant growth. The contribution of the plant growth promoting bacterium (PGPB) Azospirillum brasilense Sp6 to the growth of quailbush in compost-amended, moderately acidic, high-metal content mine tailings using an irrigation-based reclamation strategy was examined along with its influence on the rhizosphere bacterial community. Sp6 inoculation resulted in a significant (2.2-fold) increase in plant biomass production. The data suggest that the inoculum successfully colonized the root surface and persisted throughout the 60-day experiment in both the rhizosphere, as demonstrated by excision and sequencing of the appropriate denaturing gradient gel electrophoresis (DGGE) band, and the rhizoplane, as indicated by fluorescent in situ hybridization of root surfaces. Changes in rhizosphere community structure in response to Sp6 inoculation were evaluated after 15, 30, and 60 days using DGGE analysis of 16S rRNA polymerase chain reaction amplicons. A comparison of DGGE profiles using canonical correspondence analysis revealed a significant treatment effect (Sp6-inoculated vs. uninoculated plants vs. unplanted) on bacterial community structure at 15, 30, and 60 days (p < 0.05). These data indicate that in an extremely stressed environment such as acid mine tailings, an inoculated plant growth promoting bacterium not only can persist and stimulate plant growth but also can directly or indirectly influence rhizobacterial community development. © 2010 Springer Science+Business Media, LLC.
• Dowd, S. E., Halonen, M. J., & Maier, R. M. (2009). Immunological Methods. Environmental Microbiology, 225-241.
• Grandlic, C. J., Palmer, M. W., & Maier, R. M. (2009). Optimization of Plant Growth-Promoting Bacteria-Assisted Phytostabilization of Mine Tailings. Soil biology & biochemistry, 41(8), 1734-1740.
  More info

  Recent studies have indicated that plant growth-promoting bacteria (PGPB) can improve revegetation of arid mine tailings as measured by increased biomass production. The goals of the present study were first to evaluate how mode of application of known PGPB affects plant growth, and second to evaluate the effect of this inoculation on rhizosphere microbial community structure. PGPB application strategies investigated include preliminary surface sterilization of seeds (a common practice in phytoremediation trials) followed by a comparison of two application methods; immersion and alginate encapsulation. Results with two native desert plant species, Atriplex lentiformis and Buchloe dactyloides, suggest that seed surface sterilization prior to inoculation is not necessary to achieve beneficial effects of introduced PGPB. Both PGPB application techniques generally enhanced plant growth although results were both plant and PGPB specific. These results demonstrate that alginate encapsulation, which allows for long-term storage and easier application to seeds, is an effective way to inoculate PGPB. In addition, the influence of PGPB application on B. dactyloides rhizosphere community structure was evaluated using PCR-DGGE (denaturing gradient gel electrophoresis) analysis of bacterial DNA extracted from rhizosphere samples collected 75 d following planting. A comparative analysis of DGGE profiles was performed using canonical correspondence analysis (CCA). DGGE-CCA showed that rhizosphere community profiles from PGPB-inoculated treatments are significantly different from both uninoculated tailings rhizosphere profiles and profiles from the compost used to amend the tailings. Further, community profiles from B. dactyloides inoculated with the best performing PGPB (Arthro mix) were significantly different from two other PGPB tested. These results suggest that introduced PGPB have the potential to influence the development of the rhizosphere community structure found in plants grown in mine tailings.
• Grandlic, C. J., Palmer, M. W., & Maier, R. M. (2009). Optimization of plant growth-promoting bacteria-assisted phytostabilization of mine tailings. Soil Biology and Biochemistry, 41(8), 1734-1740.
  More info

  Abstract: Recent studies have indicated that plant growth-promoting bacteria (PGPB) can improve revegetation of arid mine tailings as measured by increased biomass production. The goals of the present study were first to evaluate how mode of application of known PGPB affects plant growth, and second to evaluate the effect of this inoculation on rhizosphere microbial community structure. PGPB application strategies investigated include preliminary surface sterilization of seeds (a common practice in phytoremediation trials) followed by a comparison of two application methods; immersion and alginate encapsulation. Results with two native desert plant species, Atriplex lentiformis and Buchloe dactyloides, suggest that seed surface sterilization prior to inoculation is not necessary to achieve beneficial effects of introduced PGPB. Both PGPB application techniques generally enhanced plant growth although results were both plant and PGPB specific. These results demonstrate that alginate encapsulation, which allows for long-term storage and easier application to seeds, is an effective way to inoculate PGPB. In addition, the influence of PGPB application on B. dactyloides rhizosphere community structure was evaluated using PCR-DGGE (denaturing gradient gel electrophoresis) analysis of bacterial DNA extracted from rhizosphere samples collected 75 d following planting. A comparative analysis of DGGE profiles was performed using canonical correspondence analysis (CCA). DGGE-CCA showed that rhizosphere community profiles from PGPB-inoculated treatments are significantly different from both uninoculated tailings rhizosphere profiles and profiles from the compost used to amend the tailings. Further, community profiles from B. dactyloides inoculated with the best performing PGPB (Arthro Mix) were significantly different from two other PGPB tested. These results suggest that introduced PGPB have the potential to influence the development of the rhizosphere community structure found in plants grown in mine tailings. © 2009 Elsevier Ltd. All rights reserved.
• Hayes, S. M., White, S. A., Thompson, T. L., Maier, R. M., & Chorover, J. (2009). Changes in lead and zinc lability during weathering-induced acidification of desert mine tailings: Coupling chemical and micro-scale analyses. Applied Geochemistry, 24(12), 2234-2245.
  More info

  Abstract: Desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through-flux rates. Along with other constraints, metal toxicity precludes natural plant colonization even over decadal time scales. Since unconsolidated particles can be subjected to transport by wind and water erosion, potentially resulting in direct human and ecosystem exposure, there is a need to know how the lability and form of metals change in the tailings weathering environment. A combination of chemical extractions, X-ray diffraction, micro-X-ray fluorescence spectroscopy, and micro-Raman spectroscopy were employed to study Pb and Zn contamination in surficial arid mine tailings from the Arizona Klondyke State Superfund Site. Initial site characterization indicated a wide range in pH (2.5-8.0) in the surficial tailings pile. Ligand-promoted (DTPA) extractions, used to assess plant-available metal pools, showed decreasing available Zn and Mn with progressive tailings acidification. Aluminum shows the inverse trend, and Pb and Fe show more complex pH dependence. Since the tailings derive from a common source and parent mineralogy, it is presumed that variations in pH and "bio-available" metal concentrations result from associated variation in particle-scale geochemistry. Four sub-samples, ranging in pH from 2.6 to 5.4, were subjected to further characterization to elucidate micro-scale controls on metal mobility. With acidification, total Pb (ranging from 5 to 13 g kg-1) was increasingly associated with Fe and S in plumbojarosite aggregates. For Zn, both total (0.4-6 g kg-1) and labile fractions decreased with decreasing pH. Zinc was found to be primarily associated with the secondary Mn phases manjiroite and chalcophanite. The results suggest that progressive tailings acidification diminishes the overall lability of the total Pb and Zn pools.
• Hayes, S. M., White, S. A., Thompson, T. L., Maier, R. M., & Chorover, J. (2009). Changes in lead and zinc lability during weathering-induced acidification of desert mine tailings: Coupling chemical and micro-scale analyses. Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry, 42(12), 2234-2245.
  More info

  Desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through-flux rates. Along with other constraints, metal toxicity precludes natural plant colonization even over decadal time scales. Since unconsolidated particles can be subjected to transport by wind and water erosion, potentially resulting in direct human and ecosystem exposure, there is a need to know how the lability and form of metals change in the tailings weathering environment. A combination of chemical extractions, X-ray diffraction, micro-X-ray fluorescence spectroscopy, and micro-Raman spectroscopy were employed to study Pb and Zn contamination in surficial arid mine tailings from the Arizona Klondyke State Superfund Site. Initial site characterization indicated a wide range in pH (2.5 to 8.0) in the surficial tailings pile. Ligand-promoted (DTPA) extractions, used to assess plant-available metal pools, showed decreasing available Zn and Mn with progressive tailings acidification. Aluminum shows the inverse trend, and Pb and Fe show more complex pH dependence. Since the tailings derive from a common source and parent mineralogy, it is presumed that variations in pH and "bioavailable" metal concentrations result from associated variation in particle-scale geochemistry. Four sub-samples, ranging in pH from 2.6 to 5.4, were subjected to further characterization to elucidate micro-scale controls on metal mobility. With acidification, total Pb (ranging from 5 - 13 g kg(-1)) was increasingly associated with Fe and S in plumbojarosite aggregates. For Zn, both total (0.4 - 6 g kg(-1)) and labile fractions decreased with decreasing pH. Zinc was found to be primarily associated with the secondary Mn phases manjiroite and chalcophanite. The results suggest that progressive tailings acidification diminishes the overall lability of the total Pb and Zn pools.
• Herman, D. C., & Maier, R. M. (2009). Consequences of Biogeochemical Cycles Gone Wild. Environmental Microbiology, 319-333.
• Iverson, S. L., & Maier, R. M. (2009). Effects of compost on colonization of roots of plants grown in metalliferous mine tailings, as examined by fluorescence in situ hybridization. Applied and Environmental Microbiology, 75(3), 842-847.
  More info

  PMID: 19047384;PMCID: PMC2632157;Abstract: The relationship between compost amendment, plant biomass produced, and bacterial root colonization as measured by fluorescence in situ hybridization was examined following plant growth in mine tailings. Mine tailings can remain devoid of vegetation for decades after deposition due to a combination of factors that include heavy metal toxicity, low pH, poor substrate structure and water-holding capacity, and a severely impacted heterotrophic microbial community. Research has shown that plant establishment, a desired remedial objective to reduce eolian and water erosion of such tailings, is enhanced by organic matter amendment and is correlated with significant increases in rhizosphere populations of neutrophilic heterotrophic bacteria. Results show that for the acidic metalliferous tailings tested in this study, compost amendment was associated with significantly increased bacterial colonization of roots and increased production of plant biomass. In contrast, for a Vinton control soil, increased compost had no effect on root colonization and resulted only in increased plant biomass at high levels of compost amendment. These data suggest that the positive association between compost amendment and root colonization is important in the stressed mine tailings environment where root colonization may enhance both microbial and plant survival and growth. Copyright © 2009, American Society for Microbiology. All Rights Reserved.
• Iverson, S. L., & Maier, R. M. (2009). Effects of compost on colonization of roots of plants grown in metalliferous mine tailings, as examined by fluorescence in situ hybridization. Applied and environmental microbiology, 75(3), 842-7.
  More info

  The relationship between compost amendment, plant biomass produced, and bacterial root colonization as measured by fluorescence in situ hybridization was examined following plant growth in mine tailings. Mine tailings can remain devoid of vegetation for decades after deposition due to a combination of factors that include heavy metal toxicity, low pH, poor substrate structure and water-holding capacity, and a severely impacted heterotrophic microbial community. Research has shown that plant establishment, a desired remedial objective to reduce eolian and water erosion of such tailings, is enhanced by organic matter amendment and is correlated with significant increases in rhizosphere populations of neutrophilic heterotrophic bacteria. Results show that for the acidic metalliferous tailings tested in this study, compost amendment was associated with significantly increased bacterial colonization of roots and increased production of plant biomass. In contrast, for a Vinton control soil, increased compost had no effect on root colonization and resulted only in increased plant biomass at high levels of compost amendment. These data suggest that the positive association between compost amendment and root colonization is important in the stressed mine tailings environment where root colonization may enhance both microbial and plant survival and growth.
• Maier, R. M. (2009). Bacterial Growth. Environmental Microbiology, 37-54.
• Maier, R. M. (2009). Biogeochemical Cycling. Environmental Microbiology, 287-318.
• Maier, R. M. (2009). Extreme Environments. Environmental Microbiology, 123-134.
• Maier, R. M. (2009). Microorganisms and Organic Pollutants. Environmental Microbiology, 387-420.
• Meza-Figueroa, D., Maier, R. M., de la O-Villanueva, M., Gómez-Alvarez, A., Moreno-Zazueta, A., Rivera, J., Campillo, A., Grandlic, C. J., Anaya, R., & Palafox-Reyes, J. (2009). The impact of unconfined mine tailings in residential areas from a mining town in a semi-arid environment: Nacozari, Sonora, Mexico. Chemosphere, 77(1), 140-7.
  More info

  Past mining activities in northern Mexico left a legacy of delerict landscapes devoid of vegetation and seasonal formation of salt efflorescence. Metal content was measured in mine tailings, efflorescent salts, soils, road dust, and residential soils to investigate contamination. Climatic effects such as heavy wind and rainfall events can have great impact on the dispersion of metals in semi-arid areas, since soils are typically sparsely vegetated. Geochemical analysis of this site revealed that even though total metal content in mine tailings was relatively low (e.g. Cu= 1000 mg kg(-1)), metals including Mn, Ba, Zn, and Cu were all found at significantly higher levels in efflorescence salts formed by evaporation on the tailings impoundment surface following the rainy season (e.g. Cu= 68,000 mg kg(-1)). Such efflorescent fine-grained salts are susceptible to wind erosion resulting in increased metal spread to nearby residential soils. Our results highlight the importance of seasonally dependent salt-formation and wind erosion in determining risk levels associated with potential inhalation or ingestion of airborne particulates originating from contaminated sites such as tailings impoundments. In low metal-content mine tailings located in arid and semi-arid environments, efflorescence salts could represent a human health risk and a challenge for plant establishment in mine tailings.
• Meza-Figueroa, D., Maier, R. M., de, M., Gómez-Alvarez, A., Moreno-Zazueta, A., Rivera, J., Campillo, A., Grandlic, C. J., Anaya, R., & Palafox-Reyes, J. (2009). The impact of unconfined mine tailings in residential areas from a mining town in a semi-arid environment: Nacozari, Sonora, Mexico. Chemosphere, 77(1), 140-147.
  More info

  PMID: 19500816;PMCID: PMC2737070;Abstract: Past mining activities in northern Mexico left a legacy of delerict landscapes devoid of vegetation and seasonal formation of salt efflorescence. Metal content was measured in mine tailings, efflorescent salts, soils, road dust, and residential soils to investigate contamination. Climatic effects such as heavy wind and rainfall events can have great impact on the dispersion of metals in semi-arid areas, since soils are typically sparsely vegetated. Geochemical analysis of this site revealed that even though total metal content in mine tailings was relatively low (e.g. Cu = 1000 mg kg-1), metals including Mn, Ba, Zn, and Cu were all found at significantly higher levels in efflorescence salts formed by evaporation on the tailings impoundment surface following the rainy season (e.g. Cu = 68,000 mg kg-1). Such efflorescent fine-grained salts are susceptible to wind erosion resulting in increased metal spread to nearby residential soils. Our results highlight the importance of seasonally dependent salt-formation and wind erosion in determining risk levels associated with potential inhalation or ingestion of airborne particulates originating from contaminated sites such as tailings impoundments. In low metal-content mine tailings located in arid and semi-arid environments, efflorescence salts could represent a human health risk and a challenge for plant establishment in mine tailings. © 2009 Elsevier Ltd. All rights reserved.
• Newby, D. T., Marlowe, E. M., & Maier, R. M. (2009). Nucleic Acid-Based Methods of Analysis. Environmental Microbiology, 243-284.
• Sandrin, T. R., Dowd, S. E., Herman, D. C., & Maier, R. M. (2009). Aquatic Environments. Environmental Microbiology, 103-122.
• Sandrin, T. R., Herman, D. C., & Maier, R. M. (2009). Physiological Methods. Environmental Microbiology, 191-223.
• Sun, W., Sierra-Alvarez, R., Fernandez, N., Sanz, J. L., Amils, R., Legatzki, A., Maier, R. M., & Field, J. A. (2009). Molecular characterization and in situ quantification of anoxic arsenite-oxidizing denitrifying enrichment cultures. FEMS microbiology ecology, 68(1), 72-85.
  More info

  To explore the bacteria involved in the oxidation of arsenite (As(III)) under denitrifying conditions, three enrichment cultures (ECs) and one mixed culture (MC) were characterized that originated from anaerobic environmental samples. The oxidation of As(III) (0.5 mM) was dependent on NO(3) (-) addition and N(2) formation was dependent on As(III) addition. The ratio of N(2)-N formed to As(III) fed approximated the expected stoichiometry of 2.5. A 16S rRNA gene clone library analysis revealed three predominant phylotypes. The first, related to the genus Azoarcus from the division Betaproteobacteria, was found in the three ECs. The other two predominant phylotypes were closely related to the genera Acidovorax and Diaphorobacter within the Comamonadaceae family of Betaproteobacteria, and one of these was present in all of the cultures examined. FISH confirmed that Azoarcus accounted for a large fraction of bacteria present in the ECs. The Azoarcus clones had 96% sequence homology with Azoarcus sp. strain DAO1, an isolate previously reported to oxidize As(III) with nitrate. FISH analysis also confirmed that Comamonadaceae were present in all cultures. Pure cultures of Azoarcus and Diaphorobacter were isolated and shown to be responsible for nitrate-dependent As(III) oxidation. These results, taken as a whole, suggest that bacteria within the genus Azoarcus and the family Comamonadaceae are involved in the observed anoxic oxidation of As(III).
• Grandlic, C. J., Mendez, M. O., Chorover, J., Machado, B., & Maier, R. M. (2008). Plant growth-promoting bacteria for phytostabilization of mine tailings. Environmental Science and Technology, 42(6), 2079-2084.
  More info

  PMID: 18409640;Abstract: Eolian dispersion of mine tailings in arid and semiarid environments is an emerging global issue for which economical remediation alternatives are needed. Phytostabilization, the revegetation of these sites with native plants, is one such alternative. Revegetation often requires the addition of bulky amendments such as compost which greatly increases cost. We report the use of plant growth-promoting bacteria (PGPB) to enhance the revegetation of mine tailings and minimize the need for compost amendment. Twenty promising PGPB isolates were used as seed inoculants in a series of greenhouse studies to examine revegetation of an extremely acidic, high metal content tailings sample previously shown to require 15% compost amendment for normal plant growth. Several isolates significantly enhanced growth of two native species, quailbush and buffalo grass, in tailings. In this study, PGPB/compost outcomes were plant specific; for quailbush, PGPB were most effective in combination with 10% compost addition while for buffalo grass, PGPB enhanced growth in the complete absence of compost. Results indicate that selected PGPB can improve plant establishment and reduce the need for compost amendment. Further, PGPB activities necessary for aiding plant growth in mine tailings likely include tolerance to acidic pH and metals. © 2008 American Chemical Society.
• Mendez, M. O., & Maier, R. M. (2008). Phytoremediation of mine tailings in temperate and arid environments. Reviews in Environmental Science and Biotechnology, 7(1), 47-59.
  More info

  Abstract: Phytoremediation is an emerging technology for the remediation of mine tailings, a global problem for which conventional remediation technologies are costly. There are two approaches to phytoremediation of mine tailings, phytoextraction and phytostabilization. Phytoextraction involves translocation of heavy metals from mine tailings to the plant shoot biomass followed by plant harvest, while phytostabilization focuses on establishing a vegetative cap that does not shoot accumulate metals but rather immobilizes metals within the tailings. Phytoextraction is currently limited by low rates of metal removal which is a combination of low biomass production and insufficiently high metal uptake into plant tissue. Phytostabilization is currently limited by a lack of knowledge of the minimum amendments required (e.g., compost, irrigation) to support long-term plant establishment. This review addresses both strategies within the context of two specific climate types: temperate and arid. In temperate environments, mine tailings are a source of metal leachates and acid mine drainage that contaminate nearby waterways. Mine tailings in arid regions are subject to eolian dispersion and water erosion. Examples of phytoremediation within each of these environments are discussed. Current research suggests that phytoextraction, due to high implementation costs and long time frames, will be limited to sites that have high land values and for which metal removal is required. Phytostabilization, due to lower costs and easier implementation, will be a more commonly used approach. Complete restoration of mining sites is an unlikely outcome for either approach. © 2007 Springer Science+Business Media B.V.
• Mendez, M. O., & Maier, R. M. (2008). Phytostabilization of mine tailings in arid and semiarid environments - An emerging remediation technology. Environmental Health Perspectives, 116(3), 278-283.
  More info

  PMID: 18335091;PMCID: PMC2265025;Abstract: Objective: Unreclaimed mine tailings sites are a worldwide problem, with thousands of unvegetated, exposed tailings piles presenting a source of contamination fox nearby communities. Tailings disposal sites in arid and semiarid environments are especially subject to eolian dispersion and water erosion. Phytostabilization, the use of plants for in situ stabilization of tailings and metal contaminants, is a feasible alternative to costly remediation practices. In this review we emphasize considerations for phytostabilization of mine tailings in arid and semiarid environments, as well as issues impeding its long-term success. Data sources: We reviewed literature addressing mine closures and revegetation of mine tailings, along with publications evaluating plant ecology, microbial ecology, and soil properties of mine tailings. Data extraction: Data were extracted from peer-reviewed articles and books identified in Web of Science and Agricola databases, and publications available through the U.S. Department of Agriculture, U.S. Environmental Protection Agency, and the United Nations Environment Programme. Data synthesis: Harsh climatic conditions in arid and semiarid environments along with the innate properties of mine tailings require specific considerations. Plants suitable for phytostabilization must be native, be drought-, salt-, and metal-tolerant, and should limit shoot metal accumulation. Factors for evaluating metal accumulation and toxicity issues are presented. Also reviewed are aspects of implementing phytostabilization, including plant growth stage, amendments, irrigation, and evaluation. Conclusions: Phytostabilization of mine tailings is a promising remedial technology but requires further research to identify factors affecting its long-term success by expanding knowledge of suitable plant species and mine tailings chemistry in ongoing field trials.
• Mendez, M. O., Neilson, J. W., & Maier, R. M. (2008). Characterization of a bacterial community in an abandoned semiarid lead-zinc mine tailing site. Applied and Environmental Microbiology, 74(12), 3899-3907.
  More info

  PMID: 18424534;PMCID: PMC2446573;Abstract: Bacterial diversity in mine tailing microbial communities has not been thoroughly investigated despite the correlations that have been observed between the relative microbial diversity and the success of revegetation efforts at tailing sites. This study employed phylogenetic analyses of 16S rRNA genes to compare the bacterial communities present in highly disturbed, extremely (pH 2.7) and moderately (pH 5.7) acidic lead-zinc mine tailing samples from a semiarid environment with those from a vegetated off-site (OS) control sample (pH 8). Phylotype richness in these communities decreased from 42 in the OS control to 24 in the moderately acidic samples and 8 in the extremely acidic tailing samples. The clones in the extremely acidic tailing sample were most closely related to acidophiles, none of which were detected in the OS control sample. The comparison generated by this study between the bacteria present in extremely acidic tailing and that in moderately acidic tailing communities with those in an OS control soil provides a reference point from which to evaluate the successful restoration of mine tailing disposal sites by phytostabilization. Copyright © 2008, American Society for Microbiology. All Rights Reserved.
• Ikner, L. A., Toomey, R. S., Nolan, G., Neilson, J. W., Pryor, B. M., & Maier, R. M. (2007). Culturable microbial diversity and the impact of tourism in Kartchner Caverns, Arizona. Microbial Ecology, 53(1), 30-42.
  More info

  PMID: 17186153;Abstract: Kartchner Caverns in Benson, AZ, was opened for tourism in 1999 after a careful development protocol that was designed to maintain predevelopment conditions. As a part of an ongoing effort to determine the impact of humans on this limestone cave, samples were collected from cave rock surfaces along the cave trail traveled daily by tour groups (200,000 visitors year-1) and compared to samples taken from areas designated as having medium (30-40 visitors year-1) and low (2-3 visitors year-1) levels of human exposure. Samples were also taken from fiberglass moldings installed during cave development. Culturable bacteria were recovered from these samples and 90 unique isolates were identified by using 16S rRNA polymerase chain reaction and sequencing. Diversity generally decreased as human impact increased leading to the isolation of 32, 27, and 22 strains from the low, medium, and high impact areas, respectively. The degree of human impact was also reflected in the phylogeny of the isolates recovered. Although most isolates fell into one of three phyla: Actinobacteria, Firmicutes, or Proteobacteria, the Proteobacteria were most abundant along the cave trail (77% of the isolates), while Firmicutes predominated in the low (66%) and medium (52%) impact areas. Although the abundance of Proteobacteria along the cave trail seems to include microbes of environmental rather than of anthropogenic origin, it is likely that their presence is a consequence of increased organic matter availability due to lint and other organics brought in by cave visitors. Monitoring of the cave is still in progress to determine whether these bacterial community changes may impact the future development of cave formations. © 2006 Springer Science+Business Media, Inc.
• Heo, C. H., Maier, R. M., & Curry, J. E. (2006). Directly measuring the adhesive and elastic properties of bacteria using a surface force apparatus: Effect of desiccation. Materials Research Society Symposium Proceedings, 925, 1-6.
  More info

  Abstract: Bacterial adhesion is the first step in biofilm formation which impacts numerous environmental, industrial and medical processes. Examples of undesirable consequences of biofilm formation include metal rust, sewage sludge and bacteria-related diseases. Desirable consequences are biofiltration and bioremediation. Bacteria are resilient and can survive in harsh environments. A severe stress is desiccation since dehydration can damage DNA and change the properties of proteins. Some bacteria protect against dehydration by accumulating sugars such as sucrose and trehalose while others undergo a transformation from an active to a dormant state. Evaporative deposition of bacteria on a surface shows that some bacteria aggregate to form two dimensional patterns which may be important for nutrient sharing and survival in dry conditions'. Since bacteria are increasingly being employed as components in biosensors and biofilm reactors, it is important to understand the material properties of bacteria in dry conditions for these applications. For a decade, Atomic Force Microscopy (AFM) has been the primary tool used to study the adhesion and elastic properties of individual bacteria. In this work we show it is possible to use a Surface Forces Apparatus (SFA) to measure elastic and adhesive properties of small collections of surface bound bacteria. The measurements are conducted with incomplete, patterned bacterial films and we have developed a protocol to image the contact area with AFM after the experiment. Using the SFA, we measured the force profile between a Pseudomonas aeruginosa PAO1 film and a bare mica surface. P. aeruginosa PAO1 is a . ubiquitous gram-negative soil bacterium and is also an opportunistic pathogen. We repeated the measurement in the same contact position for six days to determine the effect of desiccation on the film material properties. © 2006 Materials Research Society.
• Sandrin, T. R., Kight, W. B., Maier, W. J., & Maier, R. M. (2006). Influence of a nonaqueous phase liquid (NAPL) on biodegradation of phenanthrene. Biodegradation, 17(5), 423-435.
  More info

  PMID: 16477359;Abstract: A series of batch reactor experiments was carried out to examine the effect of a nonaqueous phase liquid (NAPL) on the biodegradation of a hydrophobic solute. A mathematical program model that describes physical processes of solute solubilization and partitioning between the NAPL and aqueous phases as well as microbial degradation and oxygen utilization was used to analyze the test data. The model calculates the cumulative changes in concentration of substrate, cell mass, carbon dioxide, and dissolved oxygen as a function of time. The equations incorporate the effects of solute solubilization, partitioning, biodegradation, as well as oxygen availability. Hexadecane was used as the model NAPL and was not biodegraded in the timeframe of the experiments performed. The model solute was the polyaromatic hydrocarbon, phenanthrene. In agreement with several previous studies, experimental measurements showed that hexadecane increased rates of mineralization of 15 mg phenanthrene when present at low mass but decreased rates at high mass. Model results suggest that partitioning of the phenanthrene into the hexadecane phase limits bioavailability at high NAPL mass. Further the model suggests that mineralization rates were higher with the low NAPL mass because aqueous phenanthrene concentrations were higher in those treatments from ca. 20 to 40 h than in other treatments. Finally, experiments showed that the presence of hexadecane, at all masses tested, resulted in a lower cell yield, effectively increasing the amount of CO2 produced during the experiment. Model results suggest that this is due to changes in phenanthrene metabolism that are induced by the presence of the hexadecane phase. Model studies aimed at increasing rates of biodegradation by modifying operating conditions are described along with practical approaches to implementing these modifications. © Springer 2006.
• Bodour, A. A., Guerrero-Barajas, C., Jiorle, B. V., Malcomson, M. E., Paull, A. K., Somogyi, A., Trinh, L. N., Bates, R. B., & Maier, R. M. (2004). Structure and Characterization of Flavolipids, a Novel Class of Biosurfactants Produced by Flavobacterium sp. Strain MTN11. Applied and Environmental Microbiology, 70(1), 114-120.
  More info

  PMID: 14711632;PMCID: PMC321267;Abstract: Herein we report the structure and selected properties of a new class of biosurfactants that we have named the flavolipids. The flavolipids exhibit a unique polar moiety that features citric acid and two cadaverine molecules. Flavolipids were produced by a soil isolate, Flavobacterium sp. strain MTN11 (accession number AY162137), during growth in mineral salts medium, with 2% glucose as the sole carbon and energy source. MTN11 produced a mixture of at least 37 flavolipids ranging from 584 to 686 in molecular weight (MW). The structure of the major component (23%; MW = 668) was determined to be 4-[[5-(7-methyl-(E)-2-octenoylhydroxyamino)pentyl]amino]-2-[2-[[5-(7-methyl-(E) -2-octenoylhydroxyamino)pentyl]amino]-2-oxoethyl]-2-hydroxy-4-oxobutanoic acid. The partially purified flavolipid mixture isolated from strain MTN11 exhibited a critical micelle concentration of 300 mg/liter and reduced surface tension to 26.0 mN/m, indicating strong surfactant activity. The flavolipid mixture was a strong and stable emulsifier even at concentrations as low as 19 mg/liter. It was also an effective solubilizing agent, and in a biodegradation study, it enhanced hexadecane mineralization by two isolates, MTN11 (100-fold) and Pseudomonas aeruginosa ATCC 9027 (2.5-fold), over an 8-day period. The flavolipid-cadmium stability constant was measured to be 3.61, which is comparable to that for organic ligands such as oxalic acid and acetic acid. In summary, the flavolipids represent a new class of biosurfactants that have potential for use in a variety of biotechnological and industrial applications.
• Haag, A. P., Maier, R. M., Combie, J., & Geesey, G. G. (2004). Bacterially derived biopolymers as wood adhesives. International Journal of Adhesion and Adhesives, 24(6), 495-502.
  More info

  Abstract: The wood adhesive market is very large and problems due to volatile organic compounds and toxic chemicals in many adhesives and their production are significant. In addition, most of the adhesives are derived from depleting petrochemical resources. An environmentally friendly wood adhesive based on renewable resources and produced by microbial fermentation has been explored. Using the shear block test method, a microbially produced polysaccharide has been tested and the effects of wood type, humidity, set time, partial acetylation, and surface wetting agents were determined. Shear strength of the microbial polysaccharide adhesive was compared to that of a commercial wood adhesive and other polysaccharides. Shear strengths of up to 20MPa (3000psi) for bonding maple have been obtained at 53% relative humidity and 22°C. © 2004 Elsevier Ltd. All rights reserved.
• Maier, R. M. (2004). Flavolipid biosurfactants. Industrial Bioprocessing, 26(2), 2-.
  More info

  Abstract: Researchers at the University of Arizona have recently determined the structure and studied the properties of a new class of biosurfactants they called flavolipids. Investigation of a partially purified flavolipid mixture isolated from the bacterial culture showed that it was a strong and stable emulsifier, even at a low concentration of 19 mg/L. The mixture exhibited a critical micelle concentration of 300 mg/liter and reduced surface tension to 26.0 mN/m. It was also an effective solubilizing agent. It enhanced biodegradation of hexadecane by two bioremediating bacteria a hundredfold.
• Bodour, A. A., Drees, K. P., & Maier, R. M. (2003). Distribution of biosurfactant-producing bacteria in undisturbed and contaminated arid southwestern soils. Applied and Environmental Microbiology, 69(6), 3280-3287.
  More info

  PMID: 12788727;PMCID: PMC161513;Abstract: Biosurfactants are a unique class of compounds that have been shown to have a variety of potential applications in the remediation of organic- and metal-contaminated sites, in the enhanced transport of bacteria, in enhanced oil recovery, as cosmetic additives, and in biological control. However, little is known about the distribution of biosurfactant-producing bacteria in the environment. The goal of this study was to determine how common culturable surfactant-producing bacteria are in undisturbed and contaminated sites. A series of 20 contaminated (i.e., with metals and/or hydrocarbons) and undisturbed soils were collected and plated on R2A agar. The 1,305 colonies obtained were screened for biosurfactant production in mineral salts medium containing 2% glucose. Forty-five of the isolates were positive for biosurfactant production, representing most of the soils tested. The 45 isolates were grouped by using repetitive extragenic palindromic (REP)-PCR analysis, which yielded 16 unique isolates. Phylogenetic relationships were determined by comparing the 16S rRNA gene sequence of each unique isolate with known sequences, revealing one new biosurfactant-producing microbe, a Flavobacterium sp. Sequencing results indicated only 10 unique isolates (in comparison to the REP analysis, which indicated 16 unique isolates). Surface tension results demonstrated that isolates that were similar according to sequence analysis but unique according to REP analysis in fact produced different surfactant mixtures under identical growth conditions. These results suggest that the 16S rRNA gene database commonly used for determining phylogenetic relationships may miss diversity in microbial products (e.g., biosurfactants and antibiotics) that are made by closely related isolates. In summary, biosurfactant-producing microorganisms were found in most soils even by using a relatively limited screening assay. Distribution was dependent on soil conditions, with gram-positive biosurfactant-producing isolates tending to be from heavy metal-contaminated or uncontaminated soils and gram-negative isolates tending to be from hydrocarbon-contaminated or cocontaminated soils.
• Dorn, J. G., Frye, R. J., & Maier, R. M. (2003). Effect of temperature, pH, and initial cell number on luxCDABE and nah gene expression during naphthalene and salicylate catabolism in the bioreporter organism Pseudomonas putida RB1353. Applied and Environmental Microbiology, 69(4), 2209-2216.
  More info

  PMID: 12676702;PMCID: PMC154800;Abstract: One limitation of employing lux bioreporters to monitor in situ microbial gene expression in dynamic, lab. oratory-scale systems is the confounding variability in the luminescent responses. For example, despite careful control of oxygen tension, growth stage, and cell number, luminescence from Pseudomonas putida RB1353, a naphthalene-degrading lux bioreporter, varied by more than sevenfold during saturated flow column experiments in our laboratory. Therefore, this study was conducted to determine what additional factors influence the luminescent response. Specifically, this study investigated the impact of temperature, pH, and initial cell number (variations within an order of magnitude) on the peak luminescence of P. putida RB1353 and the maximum degradation rate (Vmax) during salicylate and naphthalene catabolism. Statistical analyses based on general linear models indicated that under constant oxygen tension, temperature and pH accounted for 98.1% of the variability in luminescence during salicylate catabolism and 94.2 and 49.5% of the variability in Vmax during salicylate and naphthalene catabolism, respectively. Temperature, pH, and initial substrate concentration accounted for 99.9% of the variability in luminescence during naphthalene catabolism. Initial cell number, within an order of magnitude, did not have a significant influence on either peak luminescence or Vmax during salicylate and naphthalene catabolism. Over the ranges of temperature and pH evaluated, peak luminescence varied by more than 4 orders of magnitude. The minimum parameter deviation required to alter lux gene expression during salicylate and naphthalene catabolism was a change in temperature of 1°C, a change in pH of 0.2, or a change in initial cell number of 1 order of magnitude. Results from this study indicate that there is a need for careful characterization of the impact of environmental conditions on both the expression of the reporter and catabolic genes and the activities of the gene products. For example, even though lux gene expression was occurring at ∼35°C, the luciferase enzyme was inactive. Furthermore, this study demonstrates that with careful characterization and standardization of measurement conditions, the attainment of a reproducible luminescent response and an understanding of the response are feasible.
• Drees, K. P., Abbaszadegan, M., & Maier, R. M. (2003). Comparative electrochemical inactivation of bacteria and bacteriophage. Water Research, 37(10), 2291-2300.
  More info

  PMID: 12727237;Abstract: Electric fields and currents have been shown to be capable of disinfecting drinking water and reducing the numbers of bacteria and yeast in food. However, little research has been conducted regarding the effectiveness of electric fields and currents in the inactivation of viruses. The objective of this study was to compare the ability of bacteria and bacteriophage to survive exposure to direct electric current in an electrochemical cell, where they would be subject to irreversible membrane permeabilization processes, direct oxidation of cellular/viral constituents by electric current, and disinfection by electrochemically generated oxidants. Suspensions of the bacteria Escherichia coli and Pseudomonas aeruginosa and bacteriophage MS2 and PRD1 at both high (approximately 1×106CFU or PFU/mL) and low (approximately 1×103CFU or PFU/mL) population densities were exposed to currents ranging from 25 to 350mA in 5s pulses. Post-exposure plaque counts of the bacteriophage were proportionally higher than bacterial culturable counts at corresponding current exposures. E. coli and MS2 were then exposed to 5mA for 20min at both high and low population densities. The inactivation rate of E. coli was 2.1-4.3 times greater than that of MS2. Both bacteria and bacteriophage were more resistant to exposure to direct current at higher population densities. Also, amelioration of inactivation within the electrochemical cell by the reducing agent glutathione indicates the major mechanism of inactivation in the electrochemical cell is disinfection by electrochemically generated oxidants. The implications of these results are that technologies relying upon direct current to reduce the numbers of microbes in food and water may not be sufficient to reduce the numbers of potentially pathogenic viruses and ensure the safety of the treated food or water. © 2003 Elsevier Science Ltd. All rights reserved.
• Maier, R. M. (2003). Biosurfactants: Evolution and diversity in bacteria. Advances in Applied Microbiology, 52, 101-121.
  More info

  PMID: 12964241;Abstract: In summary, biosurfactants are an example of a class of microbial natural products that has coevolved among many genera. But whereas the biosurfactants produced in the bacterial and archaeal domains are convergent in function (suggesting that they are very important), they have developed in parallel with respect to genotype and phenotype (the surfactants are not related genetically or in terms of molecular structure). Because of this parallel evolution, currently available molecular screening techniques are of little use for the discovery of new biosurfactants. Development of such techniques will continue to be problematic because there is no relationship between the surfactants produced by different microbial genera and even species. Yet, the potential for application of biosurfactants and other natural products is great due to growing demand for biodegradable and environmentally friendly analogues for synthetic chemicals.
• Neilson, J. W., Artiola, J. F., & Maier, R. M. (2003). Characterization of lead removal from contaminated soils by nontoxic soil-washing agents. Journal of Environmental Quality, 32(3), 899-908.
  More info

  PMID: 12809290;Abstract: Few effective strategies exist for remediating and restoring metal-contaminated soils. We have evaluated the potential of two environmentally compatible, nondestructive, biological soil-washing agents for remediating aged, lead-contaminated soils. Two contaminated soils were washed with 10 mM rhamnolipid biosurfactant and 5.3% carboxy-methyl-β-cyclodextrin (CMCD). The metal removal efficiency of these agents was compared with 10 mM diethylenetriamine pentaacetic acid (DTPA) and 10 mM KNO3. Lead removal rates by both soil-washing agents exceeded the removal by KNO3, but were an order of magnitude less than removal by the synthetic chelator, DTPA. Analysis of soil extractions revealed that the Pb in the first soil (3780 mg kg-1) was primarily associated with the soluble, exchangeable, oxide, and residual fractions while the Pb in the second soil (23 900 mg kg-1) was found in the soluble, exchangeable, carbonate, and residual fractions. After 10 consecutive washes, rhamnolipid had removed 14.2 and 15.3% of the Pb from the first and second soils, respectively, and CMCD had removed 5 and 13.4% from the same two soils. The Pb removal rate by both agents either increased or was consistent throughout the 10 extractions, indicating a potential for continued removal with extended washing. Significant levels of Cu and Zn in both soils did not prevent Pb removal by either agent. Interestingly, the effectiveness of each agent varied as a function of Pb speciation in the soil. Rhamnolipid was more effective than CMCD in removing Pb bound to amorphous iron oxides, while both agents demonstrated similar potential for removing soluble, exchangeable, and carbonate-bound Pb. Neither agent demonstrated potential for the complete remediation of metal-contaminated soils.
• Rensing, C., & Maier, R. M. (2003). Issues underlying use of biosensors to measure metal bioavailability. Ecotoxicology and Environmental Safety, 56(1), 140-147.
  More info

  PMID: 12915147;Abstract: Heavy metal-mediated toxicity in the environment is dependent on bioavailable metal concentrations both internal and external to microbial cells. Both internal and external metal bioavailability are influenced by multiple factors in the soil environment. External factors include pH, redox potential, ionic strength, organic matter and clay content. The internal bioavailable metal concentration is dependent on both the aforementioned external factors, as well as metal uptake and efflux activities that are specific for each microorganism. The metal-specific biosensors discussed in this article can be used to measure internal metal bioavailability. © 2003 Elsevier Inc. All rights reserved.
• Sandrin, T. R., & Maier, R. M. (2003). Impact of metals on the biodegradation of organic pollutants. Environmental Health Perspectives, 111(8), 1093-1101.
  More info

  PMID: 12826480;PMCID: PMC1241557;Abstract: Forty percent of hazardous waste sites in the United States are co-contaminated with organic and metal pollutants. Data from both aerobic and anaerobic systems demonstrate that biodegradation of the organic component can be reduced by metal toxicity. Metal bioavailability, determined primarily by medium composition/soil type and pH, governs the extent to which metals affect biodegradation. Failure to consider bioavailability rather than total metal likely accounts for much of the enormous variability among reports of inhibitory concentrations of metals. Metals appear to affect organic biodegradation through impacting both the physiology and ecology of organic degrading microorganisms. Recent approaches to increasing organic biodegradation in the presence of metals involve reduction of metal bioavailability and include the use of metal-resistant bacteria, treatment additives, and clay minerals. The addition of divalent cations and adjustment of pH are additional strategies currently under investigation.
• Sandrin, T. R., & Maier, R. M. (2002). Effect of pH on cadmium toxicity, speciation, and accumulation during naphthalene biodegradation. Environmental Toxicology and Chemistry, 21(10), 2075-2079.
  More info

  PMID: 12371483;Abstract: Lowering pH of a microbiological medium from 7 to 4 decreased cadmium toxicity during naphthalene biodegradation by a Burkholderia sp. Cadmium speciation and cadmium accumulation in the system were studied to explain this effect. Cadmium speciation was determined by direct measurement and by geochemical modeling. Previous studies have implicated the monovalent hydroxylated cadmium (CdOH+) species in the effect of pH on cadmium toxicity. Modeling analysis predicted CdOH+ formation only at very low concentrations (≤0.0128 μM), while the measured concentration of divalent ionic cadmium (Cd2+) was at least three orders of magnitude greater, suggesting that Cd2+ is the more significant metal form. With respect to cadmium accumulation, cells contained in media adjusted to pH 4 accumulated only 2.76 ± 0.76 mg Cd/g cells, whereas cells in media adjusted to pH 7 accumulated 8.52 ± 0.71 mg Cd/g cells. These data suggest that cadmium toxicity is correlated with increased cadmium accumulation rather than the formation of CdOH+ as pH is increased. At low pH, the decrease in cadmium accumulation may be caused by increased competition between hydrogen and cadmium ions for binding sites on the cell surface or by an increase in metal efflux pump activity due to an increase in the proton gradient that drives the efflux pump.
• Maier, R. M., Neilson, J. W., Artiola, J. F., Jordan, F. L., Gleen, E. P., & Descher, S. M. (2001). Remediation of metal-contaminated soil and sludge using biosurfactant technology. International Journal of Occupational Medicine and Environmental Health, 14(3), 241-248.
  More info

  PMID: 11764852;Abstract: Development of environmentally benign approaches to remediation of metal-contaminated soils and sewage sludges are needed to replace currently used techniques of either landfilling or metal extraction using caustic or toxic agents. We report results from four application technologies that use a metal-chelating biosurfactant, rhamnolipid, for removal of metals or metal-associated toxicity from metal-contaminated waste. The four applications include: 1) removal of metals from sewage sludge; 2) removal of metals from historically contaminated soils; 3) combined biosurfactant/phytoremediation of metal-contaminated soil; and 4) use of biosurfactant to facilitate biodegradation of the organic component of a metal-organic co-contaminated soil (in this case the biosurfactant reduces metal toxicity). These four technologies are nondestructive options for situations where the final goal is the removal of bioavailable and leachable metal contamination while maintaining a healthy ecosystem. Some of the approaches outlined may require multiple treatments or long treatment times which must be acceptable to site land-use plans and to the stakeholders involved. However, the end-product is a soil, sediment, or sludge available for a broad range of land use applications.
• Ochoa-Loza, F., Artiola, J. F., & Maier, R. M. (2001). Stability constants for the complexation of various metals with a rhamnolipid biosurfactant. Journal of Environmental Quality, 30(2), 479-485.
  More info

  PMID: 11285908;Abstract: The presence of toxic metals in natural environments presents a potential health hazard for humans. Metal contaminants in these environments are usually tightly bound to colloidal particles and organic matter. This represents a major constraint to their removal using currently available in situ remediation technologies. One technique that has shown potential for facilitated metal removal from soil is treatment with an anionic microbial surfactant, rhamnolipid. Successful application of rhamnolipid in metal removal requires knowledge of the rhamnolipid-metal complexation reaction. Therefore, our objective was to evaluate the biosurfactant complexation affinity for the most common natural soil and water cations and for various metal contaminants. The conditional stability constant (log K) for each of these metals was determined using an ion-exchange resin technique. Results show the measured stability constants follow the order (from strongest to weakest):Al3+ > Cu2+ > Pb2+ > Cd2+ > Zn2+ > Fe3+ > Hg2+ > Ca2+ > Co2+ > Ni2+ > Mn2+> Mg2+ > K+. These data indicate that rhamnolipid will preferentially complex metal contaminants such as lead, cadmium, and mercury in the presence of common soil or water cations. The measured rhamnolipid-metal stability constants were found in most cases to be similar or higher than conditional stability constants reported in the literature for metal complexation with acetic acid, oxalic acid, citric acid, and fulvic acids. These results help delineate the conditions under which rhamnolipid may be successfully applied as a remediation agent in the removal of metal contaminants from soil, as well as surface waters, ground water, and wastestreams.
• Al-Tahhan, R., Sandrin, T. R., Bodour, A. A., & Maier, R. M. (2000). Rhamnolipid-induced removal of lipopolysaccharide from Pseudomonas aeruginosa: Effect on cell surface properties and interaction with hydrophobic substrates. Applied and Environmental Microbiology, 66(8), 3262-3268.
  More info

  PMID: 10919779;PMCID: PMC92143;Abstract: Little is known about the interaction of biosurfactants with bacterial cells. Recent work in the area of biodegradation suggests that there are two mechanisms by which biosurfactants enhance the biodegradation of slightly soluble organic compounds. First, biosurfactants can solubilize hydrophobic compounds within micelle structures, effectively increasing the apparent aqueous solubility of the organic compound and its availability for uptake by a cell. Second, biosurfactants can cause the cell surface to become more hydrophobic, thereby increasing the association of the cell with the slightly soluble substrate. Since the second mechanism requires very low levels of added biosurfactant, it is the more intriguing of the two mechanisms from the perspective of enhancing the biodegradation process. This is because, in practical terms, addition of low levels of biosurfactants will be more cost-effective for bioremediation. To successfully optimize the use of biosurfacrants in the bioremediation process, their effect on cell surfaces must be understood. We report here that rhamnolipid biosurfactant causes the cell surface of Pseudomonas spp. to become hydrophobic through release of lipopolysaccharide (LPS). In this study, two Pseudomonas aeruginosa strains were grown on glucose and hexadecane to investigate the chemical and structural changes that occur in the presence of a rhamnolipid biosurfactant. Results showed that rhamnolipids caused an overall loss in cellular fatty acid content. Loss of fatty acids was due to release of LPS from the outer membrane, as demonstrated by 2-keto-3-deoxyoctonic acid and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and further confirmed by scanning electron microscopy. The amount of LPS loss was found to be dependent on rhamnolipid concentration, but significant loss occurred even at concentrations less than the critical micelle concentration. We conclude that rhamnolipid-induced LPS release is the probable mechanism of enhanced cell surface hydrophobicity.
• Maier, R. M., & Soberón-Chávez, G. (2000). Pseudomonas aeruginosa rhamnolipids: Biosynthesis and potential applications. Applied Microbiology and Biotechnology, 54(5), 625-633.
  More info

  PMID: 11131386;Abstract: Pseudomonas aeruginosa produces and secretes rhamnose-containing glycolipid biosurfactants called rhamnolipids. This review describes rhamnolipid biosynthesis and potential industrial and environmental applications of rhamnolipids. Rhamnolipid production is dependent on central metabolic pathways, such as fatty acid synthesis and dTDP-activated sugars, as well as on enzymes participating in the production of the exopolysaccharide alginate. Synthesis of these surfactants is regulated by a very complex genetic regulatory system that also controls different P. aeruginosa virulence-associated traits. Rhamnolipids have several potential industrial and environmental applications including the production of fine chemicals, the characterization of surfaces and surface coatings, as additives for environmental remediation, and as a biological control agent. Realization of this wide variety of applications requires economical commercial-scale production of rhamnolipids.
• Maslin, P., & Maier, R. M. (2000). Rhamnolipid-enhanced mineralization of phenanthrene in organic-metal co-contaminated soils. Bioremediation Journal, 4(4), 295-308.
  More info

  Abstract: Successful remediation of soils co-contaminated with organics and metals may require a combination of technologies. This research addresses the organic component within co-contaminated sites. It is well known that metal contaminants in soil can partially or completely inhibit normal helerotrophic microbial activity and hence prevent in situ biodegradation of organics. Previous work has shown that a rhamnolipid biosurfactant can complex metals such as lead and cadmium. It has also been demonstrated, in pure culture, that rhamnolipid can mitigate metal inhibition during the degradation of naphthalene. The goal of this study was to investigate whether rhamnolipid could reduce the toxicity of a model metal, cadmium, to indigenous soil populations in two different soils, Brazito and Gila, during the mineralization of phenanthrene. Results show that cadmium inhibited phenanthrene mineralization in both soils at bioavailable cadmium concentrations as low as 27 μM. This inhibition was reduced by the addition of rhamnolipid. Since rhamnolipid is degraded by soil populations, a rhamnolipid pulsing strategy was used to maintain a constant level of rhamnolipid in the system. Using this strategy, phenanthrene mineralization levels comparable to the control (0 mM Cd/0 mM rhamnolipid) were achieved in the presence of toxic cadmium concentrations. This research demonstrates that pulsed application of rhamnolipid may allow bioremedialion of organic contaminants in sites that are co-contaminated with organics and metals.
• Sandrin, T. R., Chech, A. M., & Maier, R. M. (2000). A rhamnolipid biosurfactant reduces cadmium toxicity during naphthalene biodegradation. Applied and Environmental Microbiology, 66(10), 4585-4588.
  More info

  PMID: 11010924;PMCID: PMC92350;Abstract: A model cocontaminated system was developed to determine whether a metal-complexing biosurfactant, rhamnolipid, could reduce metal toxicity to allow enhanced organic biodegradation by a Burkholderia sp. isolated from soil. Rhamnolipid eliminated cadmium toxicity when added at a 10-fold greater concentration than cadmium (890 μM), reduced toxicity when added at an equimolar concentration (89 μM), and had no effect at a 10-fold smaller concentration (8,9 μM). The mechanism by which rhamnolipid reduces metal toxicity may involve a combination of rhamnolipid complexation of cadmium and rhamnolipid interaction with the cell surface to alter cadmium uptake.
• Jordan, F. L., & Maier, R. M. (1999). Development of an agar lift-DNA/DNA hybridization technique for use in visualization of the spatial distribution of Eubacteria on soil surfaces. Journal of Microbiological Methods, 38(1-2), 107-117.
  More info

  PMID: 10520591;Abstract: While microbial growth is well-understood in pure culture systems, less is known about growth in intact soil systems. The objective of this work was to develop a technique to allow visualization of the two-dimensional spatial distribution of bacterial growth on a homogenous soil surface. This technique is a two-step process wherein an agar lift is taken and analyzed using a universal gene probe. An agar lift is comprised of a thin layer of soil that is removed from a soil surface using an agar slab. The agar is incubated to allow for microbial growth, after which, colonies are transferred to a membrane for conventional bacterial colony DNA/DNA hybridization analysis. In this study, a eubacterial specific probe was used to demonstrate that growing bacterial populations on soil surfaces could be visualized. Results show that microbial growth and distribution was nonuniform across the soil surface. Spot supplementation of the soil with benzoate or glucose resulted in a localized microbial growth response. Since only growing colonies are detected, this technique should facilitate a greater understanding of the microbial distribution and its response to substrate addition in more heterogenous soil systems.
• Neilson, J. W., Pierce, S. A., & Maier, R. M. (1999). Factors influencing expression of luxCDABE and nah genes in Pseudomonas putida RB1353(NAH7, pUTK9) in dynamic systems. Applied and Environmental Microbiology, 65(8), 3473-3482.
  More info

  PMID: 10427037;PMCID: PMC91522;Abstract: Bioluminescent reporter organisms have been successfully exploited as analytical tools for in situ determination of bioavailable levels of contaminants in static environmental samples. Continued characterization and development of such reporter systems is needed to extend the application of these bioreporters to in situ monitoring of degradation in dynamic environmental systems. In this study, the naphthalene-degrading, lux bioreporter bacterium Pseudomonas putida RB1353 was used to evaluate the relative influences of cell growth stage, cell density, substrate concentration, oxygen tension, and background carbon substrates on both the magnitude of the light response and the rate of salicylate disappearance. The effect of these variables on the lag time required to obtain maximum luminescence and degradation was also monitored. Strong correlations were observed between the first three factors and both the magnitude and induction time of luminescence and degradation rate. The maximum luminescence response to nonspecific background carbon substrates (soil extract broth or Luria broth) was 50% lower than that generated in response to 1 mg of sodium salicylate liter-1. Oxygen tension was evaluated over the range of 0.5 to 40 mg liter-1, with parallel inhibition to luminescence and degradation rate (20 mg of sodium salicylate liter-1) observed at 1.5 mg liter-1 and below and no effect observed above 5 mg liter-1. Oxygen tensions from 2 to 4 mg liter-1 influenced the magnitude of luminescence but not the salicylate degradation rate. The results suggest that factors causing parallel shifts in the magnitude of both luminescence and degradation rate were influencing regulation of the nah operon promoters. For factors that cause nonparallel shifts, other regulatory mechanisms are explored. This study demonstrates that lux reporter bacteria can be used to monitor both substrate concentration and metabolic response in dynamic systems. However, each lux reporter system and application will require characterization and calibration.
• Bodour, A. A., & Miller-Maier, R. M. (1998). Application of a modified drop-collapse technique for surfactant quantitation and screening of biosurfactant-producing microorganisms. Journal of Microbiological Methods, 32(3), 273-280.
  More info

  Abstract: A drop-collapse method has been refined for use as both a qualitative assay to screen for surfactant-producing microbes, and as a quantitative assay to determine surfactant concentration. The assay is rapid, easy to perform, reproducible and requires little specialized equipment. The assay is performed in a 96-microwell plate, where each well is thinly coated with oil. A 5 μL sample droplet is added to the center of a well and observed after 1 min. The droplet will either bead up, spread out slightly or collapse, depending on the amount of surfactant in the sample. The basis for this method is the type of oil used to coat each well. In the qualitative method, each well is coated with 1.8 μL of Pennzoil® and either the drop collapses, indicating the presence of surfactant (a positive result), or the drop remains beaded, indicating the absence of surfactant (a negative response). In the quantitative method, each well is coated with 2 μL of mineral oil, and a dissecting microscope is used to measure the diameter of the droplet at 1 min. Results with both a test biosurfactant (rhamnolipid) and a test synthetic surfactant (sodium dodecyl sulfate) indicate a direct linear correlation between droplet diameter and surfactant concentration. The drop-collapse method has several advantages over commonly used methods that measure surface tension, such as the du Nouy ring method; a smaller volume is required (5 μL vs. 20 mL), the effective range of measurement is greater and it does not require specialized equipment. Copyright (C) 1998 Elsevier Science B.V.
• Campos-García, J., Caro, A. D., Nájera, R., Miller-Maier, R. M., Al-Tahhan, R. A., & Soberón-Chávez, G. (1998). The Pseudomonas aeruginosa rhlG gene encodes an NADPH-dependent β- ketoacyl reductase which is specifically involved in rhamnolipid synthesis. Journal of Bacteriology, 180(17), 4442-4451.
  More info

  PMID: 9721281;PMCID: PMC107453;Abstract: A Pseudomonas aeruginosa gene homologous to the fabG gene, which encodes the NADPH-dependent β-ketoacyl-acyl carrier protein (ACP) reductase required for fatty acid synthesis, was identified. The insertional mutation of this fabG homolog (herein called rhlG) produced no apparent effect on the growth rate and total lipid content of P. aeruginosa cells, but the production of rhamnolipids was completely abrogated. These results suggest that the synthetic pathway for the fatty acid moiety of rhamnolipids is separate from the general fatty acid synthetic pathway, starting with a specific ketoacyl reduction step catalyzed by the RhlG protein. In addition, the synthesis of poly-β-hydroxyalkanoate (PHA) is delayed in this mutant, suggesting that RhlG participates in PHA synthesis, although it is not the only reductase involved in this pathway. Traits regulated by the quorum-sensing response, other than rhamnolipid production, including production of proteases, pyocyanine, and the autoinducer butanoyl-homoserine lactone (PAI-2), were not affected by the rhlG mutation. We conclude that the P. aeruginosa rhlG gene encodes an NADPH-dependent β-ketoacyl reductase absolutely required for the synthesis of the β-hydroxy acid moiety of rhamnolipids and that it has a minor role in PHA production. Expression of rhlG mRNA under different culture conditions is consistent with this conclusion.
• Torrens, J. L., Herman, D. C., & Miller-Maier, R. M. (1998). Biosurfactant (Rhamnolipid) sorption and the impact on rhamnolipid- facilitated removal of cadmium from various soils under saturated flow conditions. Environmental Science and Technology, 32(6), 776-781.
  More info

  Abstract: The efficiency of biosurfactant-facilitated removal of soil-bound metals is affected by biosurfactant sorption to soil. In this study, batch and column experiments were performed to minimize rhamnolipid biosurfactant sorption and to optimize rhamnolipid application for removal of cadmium from four soils. In batch studies, rhamnolipid sorption to a model coarse loamy soil was found to vary with applied rhamnolipid and K+ concentration of the rhamnolipid matrix. The presence of solution-phase biosurfactant was correlated to the release into solution of a soil-bound metal (cadmium). A series of column experiments was performed to evaluate whether rhamnolipid could remove cadmium from soil under saturated flow conditions. Four different soils were contaminated with cadmium and treated first with an KNO3 electrolyte solution (3.5 or 7 mM K+) and then with a rhamnolipid- containing solution (5 or 10 mM). Results showed that between 15 and 36% of the cadmium was removed by the initial electrolyte treatment and an additional 8-54% of the cadmium was removed by rhamnolipid treatment. Rhamnolipid treatment was very effective for three of the soils tested, but for the soil with the highest clay content, rhamnolipid application caused soil dispersion and column plugging.
• Herman, D. C., Lenhard, R. J., & Miller, R. M. (1997). Formation and removal of hydrocarbon residual in porous media: Effects of attached bacteria and biosurfactants. Environmental Science and Technology, 31(5), 1290-1294.
  More info

  Abstract: Column studies were used to investigate the fate of a representative nonaqueous-phase liquid (NAPL), hexadecane, with specific regard to (1) the effect of attached bacteria on the formation of residual saturation and (2) the role of biodegradation and biosurfactants on the removal of residual NAPL. Residual saturation of hexadecane was determined using sterile sand (40/50 mesh) columns and was found to be 19.0 ± 4.8% of the pore volume. Columns loaded with bacterial biomass (Pseudomonas aeruginosa ATCC 15442, 109 cells g-1) showed no difference in residual hexadecane formation as compared to sterile sand columns. In further column studies examining the effect of ATCC 15442 and biosurfactants on the removal of hexadecane residual, results showed that biodegradation alone removed approximately 50% of the [14C]hexadecane, in the form of 14CO2 and undefined cellular metabolites, during elution with at least 200 pore volumes of mineral salts medium. The columns were then eluted with 1 mM rhamnolipid biosurfactant, which increased total removal to 65%. Rhamnolipid addition resulted in (1) the mobilization of hexadecane free product and (2) a transitory 3-12-fold increase in the rate of hexadecane mineralization. In a separate study, the column was eluted from the beginning with a low (0.1 mM) concentration of rhamnolipid. This lower concentration of biosurfactant enhanced the removal of hexadecane by mobilization, but had no effect on the rate of biodegradation of residual hexadecane. Analysis of residual radioactivity within two columns revealed only 2% remaining as intact hexadecane. These results suggest that a combination of biodegradation and rhamnolipid treatment could be used to maximize the removal of residual NAPL from porous media.
• Herman, D. C., Zhang, Y., & Miller, R. M. (1997). Rhamnolipid (biosurfactant) effects on cell aggregation and biodegradation of residual hexadecane under saturated flow conditions. Applied and Environmental Microbiology, 63(9), 3622-3627.
  More info

  PMID: 9293014;PMCID: PMC168669;Abstract: The objective of this research was to evaluate the effect of low concentrations of a rhamnolipid biosurfactant on the in situ biodegradation of hydrocarbon entrapped in a porous matrix. Experiments were performed with sand-packed columns under saturated flow conditions with hexadecane as a model hydrocarbon. Application of biosurfactant concentrations greater than the CMC (the concentration at which the surfactant molecules spontaneously farm micelles or vesicles [0.03 mM]) resulted primarily in the mobilization of hexadecane entrapped within the sand matrix. In contrast, application of biosurfactant concentrations less than the CMC enhanced the in situ mineralization of entrapped hexadecane; however, this effect was dependent on the choice of bacterial isolate. The two Pseudomonas isolates tested, R4 and ATCC 15524, were used because they exhibit different patterns of biodegradation of hexadecane, and they also differed in their physical response to rhamnolipid addition. ATCC 15524 cells formed extensive multicell aggregates in the presence of rhamnolipid while R4 cells were unaffected. This behavior did not affect the ability of the biosurfactant to enhance the biodegradation of hexadecane in well-mixed soil slurry systems but had a large affect on the extent of entrapped hexadecane biodegradation in the sand-packed-column system that was used in this study.
• Miller, J. L., Sardo, M. A., Thompson, T. L., & Miller, R. M. (1997). Effect of application solvents on heterotrophic and nitrifying populations in soil microcosms. Environmental Toxicology and Chemistry, 16(3), 447-451.
  More info

  Abstract: Agricultural practices may cause contamination of soil and ground water with a combination of organic compounds (pesticides and fuel) and nitrogen fertilizers. In coupled microcosm studies that monitored the mineralization of naphthalene and the nitrification of ammonia, it was observed that the solvent (dichloromethane) used to apply naphthalene to the soil inhibited nitrification, although there was no effect on naphthalene mineralization. Further studies were performed with a series of application solvents: methanol, acetonitrile, trichloromethane, and dichloromethane. Soil and solvent were allowed to equilibrate with ambient air for various times before capping and incubation of microcosm. Results indicated that dichloromethane equilibrated for 5 mins inhibited nitrification for at least 3 weeks relative to the control (water). Acetonitrile and trichloromethane similarly inhibited nitrification. Methanol and dichloromethane equilibrated for 60 mins also significantly delayed nitrification, although to a lesser extent. Inhibition of nitrification was not permanent, and nitrification activity was eventually restored in all systems tested. None of the solvents inhibited mineralization of the added carbon source. These results indicate that special care must be taken to ensure that applications solvents do not affect the activity of sensitive microbial populations, such as the nitrifiers, that may be part of a study.
• Stanghellini, M. E., & Miller, R. M. (1997). Their identity and potential efficacy in the biological control of zoosporic plant pathogens. Plant Disease, 81(1), 4-12.
• Wild, M., Caro, A. D., Hernández, A. L., Miller, R. M., & Soberón-Chávez, G. (1997). Selection and partial characterization of a Pseudomonas aeruginosa mono- rhamnolipid deficient mutant. FEMS Microbiology Letters, 153(2), 279-285.
  More info

  PMID: 9271853;Abstract: Pseudomonas aeruginosa produces rhamnolipids which are tenso-active compounds with potential industrial and environmental applications. There are two main types of rhamnolipids produced in liquid cultures, rhamnosyl-β- hydroxydecanoyl-β-hydroxydecanoate (mono-rhamnolipid) and rhamnosyl- rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (di-rhamnolipid). In this work we report the selective isolation of a rhamnolipid deficient mutant (IBT8), which does not accumulate mono-rhamnolipid while still producing di- rhamnolipid. IBT8 was selected after random mutagenesis with Tn501; yet, its mono-rhamnolipid deficiency was found associated neither with its Tn501 insertion nor with a possible alteration in the rhlABRI genes for rhamnosyl- transferase 1 synthesis. Different possibilities to explain IBT8 phenotype are discussed.
• Zhang, Y., Maier, W. J., & Miller, R. M. (1997). Effect of rhamnolipids on the dissolution, bioavailability, and biodegradation of phenanthrene. Environmental Science and Technology, 31(8), 2211-2217.
  More info

  Abstract: Biodegradation rates for polycyclic aromatic hydrocarbons (PAH) in the environment are limited by their low solubility and sorption to solid surfaces. The purpose of this study was to quantify the effect of biosurfactants on the dissolution, bioavailability, and biodegradation of a slightly soluble PAH, phenanthrene, in a series of batch solution studies. A mathematical model that describes the combined effects of solubilization and biodegradation, including description of bioavailability within surfactant micelles, was used to analyze the experimental results. Two forms of the biosurfactant, a monorhamnolipid and a dirhamnolipid, were tested; it was found that both surfactants increased the solubility and enhanced the rate of phenanthrene biodegradation. Monorhamnolipid was more effective than dirhamnolipid for solubilization; however, overall rates of mineralization were essentially the same. This seems to result from variable bioavailability of substrate: phenanthrene within monorhamnolipid micelles was less bioavailable than phenanthrene within dirhamnolipid micelles. Therefore, the effect of a surfactant on biodegradation is s combination of the solubilizing power of the surfactant and the bioavailability of the substrate within the surfactant micelles. Model analysis of the solubilization data showed that the overall solubilization rate coefficient, K(L), increased with increasing biosurfactant concentration. Analysis of biodegradation data showed that enhanced biodegradation rates depend upon both K(L) and α, the coefficient for substrate bioavailability from micelles. Model simulations using parameters developed from test data are discussed.
• Champion, J. T., Gilkey, J. C., Lamparski, H., Retterer, J., & Miller, R. M. (1995). Electron microscopy of rhamnolipid (biosurfactant) morphology: effects of pH, cadmium, and octadecane. Journal of Colloid and Interface Science, 170(2), 569-574.
  More info

  Abstract: It was previously reported that rhamnolipid bisurfactant from Pseudomonas aeruginosa ATCC 9027 can be used to remediate contaminated sites. Since the effective use of rhamnolipid require an understanding of its morphology as well as the effects of pH and organic and inorganic contaminants on that morphology, cryo-transmission electron microscopy was used to examine the morphology of vitrified, frozen hydrated suspensions of rhamnolipid over a pH range of 5.5 to 8.0. The effect of a model alkane, octadecane and a model heavy metal cadmium on the morphology of the rhamnolipid was also determined. Results obtained are found to be satisfactory.
• Herman, D. C., Artiola, J. F., & Miller, R. M. (1995). Removal of cadmium, lead, and zinc from soil by a rhamnolipid biosurfactant. Environmental Science and Technology, 29(9), 2280-2285.
  More info

  Abstract: Complexation of cadmium, lead, and zinc (singly and in a mixture) by a monorhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 was studied in batch solution and soil experiments. Conditional stability constants (log K(L)) for metal-rhamnolipid complexation in a buffered medium (0.1 M Pipes, pH 6.8) were determined in duplicate using an ion-exchange technique and averaged 6.5 (Cd2+), 6.6 (Pb2+), and 5.4 (Zn2+); these values are similar or slightly higher than literature values for Cd2+ and Pb2+ complexation with fulvic acid and activated sludge solids. To determine the ability of rhamnolipid to desorb soil-bound metals, rhamnolipid solutions (12.5, 25, 50, and 80 mM) were added to soil containing sorbed Cd2+ (1.46 mmol kg-1), Pb2+ (1.96 mmol kg-1), or a mixture of Pb2+- Cd2+-Zn2+ (3.4 mmol kg-1). At 12.5 and 25 mM rhamnolipid, rhamnolipid sorption to soil exceeded 78%, and less than 11% of soil-bound Cd2+ and Zn2+ was desorbed. However, ion exchange of bound metals with K+ present in the rhamnolipid matrix could account for the removal of between 16 and 48% of the sorbed Cd2+ and Zn2+. At 50 and 80 mM rhamnolipid, rhamnolipid sorption to soil decreased to between 20 and 77%, and the removal of Cd2+ and Zn2+ could exceed the removal by ion exchange by as much as 3-fold. The behavior of Pb2+ was quite different. Less than 2% of soil-bound Pb2+ was desorbed due to ion exchange, although up to 43% was desorbed by 80 mM rhamnolipid.
• Miller, R. M. (1995). Biosurfactant-facilitated remediation of metal-contaminated soils. Environmental Health Perspectives, 103(SUPPL. 1), 59-62.
  More info

  PMID: 7621801;PMCID: PMC1519337;Abstract: Bioremediation of metal-contaminated wastestreams has been successfully demonstrated. Normally, whole cells or microbial exopolymers are used to concentrate and/or precipitate metals in the wastestream to aid in metal removal. Analogous remediation of metal-contaminated soils is more complex because microbial cells or large exopolymers do not move freely through the soil. The use of microbially produced surfactants (biosurfactants) is an alternative with potential for remediation of metal-contaminated soils. The distinct advantage of biosurfactants over whole cells or exopolymers is their small size, generally biosurfactant molecular weights are less than 1500. A second advantage is that biosurfactants have a wide variety of chemical structures that may show different metal selectivities and thus, metal removal efficiencies. A review of the literature shows that complexation capacities of several bacterial exopolymers was similar to the complexation capacity of a rhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027.
• Zhang, Y., & Miller, R. M. (1995). Effect of rhamnolipid (biosurfactant) structure on solubilization and biodegradation of n-alkanes. Applied and Environmental Microbiology, 61(6), 2247-2251.
  More info

  PMID: 16535047;PMCID: PMC1388465;Abstract: A study to quantify the effect of rhamnolipid biosurfactant structure on the degradation of alkanes by a variety of Pseudomonas isolates was conducted. Two dirhamnolipids were studied, a methyl ester form (dR-Me) and an acid form (dR-A). These rhamnolipids have different properties with respect to interfacial tension, solubility, and charge. For example, the interfacial tension between hexadecane and water was decreased to
• Zhang, Y., & Miller, R. M. (1994). Effect of a Pseudomonas rhamnolipid biosurfactant on cell hydrophobicity and biodegradation of octadecane. Applied and Environmental Microbiology, 60(6), 2101-2106.
  More info

  PMID: 8031099;PMCID: PMC201607;Abstract: In this study, the effect of a purified rhamnolipid biosurfactant on the hydrophobicity of octadecane-degrading cells was investigated to determine whether differences in rates of octadecane biodegradation resulting from the addition of rhamnolipid to four strains of Pseudomonas aeruginosa could be related to measured differences in hydrophobicity. Cell hydrophobicity was determined by a modified bacterial adherence to hydrocarbon (BATH) assay. Bacterial adherence to hydrocarbon quantitates the preference of cell surfaces for the aqueous phase or the aqueous-hexadecane interface in a two- phase system of water and hexadecane. On the basis of octadecane biodegradation in the absence of rhamnolipid, the four bacterial strains were divided into two groups: the fast degraders (ATCC 15442 and ATCC 27853), which had high cell hydrophobicities (74 and 55% adherence to hexadecane, respectively), and the slow degraders (ATCC 9027 and NRRL 3198), which had low cell hydrophobicities (27 and 40%, respectively). Although in all cases rhamnolipid increased the aqueous dispersion of octadecane at least 104- fold, at low rhamnolipid concentrations (0.6 mM), biodegradation by all four strains was initially inhibited for at least 100 h relative to controls. At high rhamnolipid concentrations (6 mM), biodegradation by the fast degraders was slightly inhibited relative to controls, but the biodegradation by the slow degraders was enhanced relative to controls. Measurement of cell hydrophobicity showed that rhamnolipids increased the cell hydrophobicity of the slow degraders but had no effect on the cell hydrophobicity of the fast degraders. The rate at which the cells became hydrophobic was found to depend on the rhamnolipid concentration and was directly related to the rate of octadecane biodegradation. These results suggest that the bioavailability of octadecane in the presence of rhamnolipid is controlled by both aqueous dispersion of octadecane and cell hydrophobicity.
• Miller, R. M., Stitzer, L. S., Artiola, J. F., & Fuller, W. H. (1992). Effect of four alcohols on adsorption, desorption, and movement of cadmium, nickel, and zinc through soils. Chemosphere, 24(12), 1855-1866.
  More info

  Abstract: Miscible-displacement experiments were conducted to compare the effects of aqueous soil solutions with ethyl alcohol, ethylene glycol, diethylene glycol, and triethylene glycol on the movement of metals through soils. Aqueous or alcohol solutions containing 1 mM each Cd, Ni, and Zn and 5 mM Ca were perfused through columns containing River Sand, Canelo loam (Canelo I) or Mohave sandy clay loam (Mohave scl) until effluent metal concentrations (C) equaled influent concentrations (CO) or CC0-1 = 1. In general, the order of sorption was Zn > Ni > Cd in aqueous-perfused columns, while in alcohol-perfused columns sorption of M > > Cd ≥ Zn. In comparison to aqueous solutions, alcohols reduced total metal sorption by at least 25%. Metal sorption was best correlated to cation exchange capacity of the soil, sorption of metals being greatest in the Mohave scl and least in the River Sand. After CC0-1 = 1 was reached, columns were leached with deionized water. While leaching did not affect the sorption of metals in columns which had been perfused with aqueous solvents, sorption behavior of metals changed significantly in columns which had been perfused with alcohol solvents. Leaching caused desorption of 5 to 30% of the sorbed Ni. In general, Cd was desorbed (up to 45%) from the soils tested. The exceptions were River Sand columns perfused with diethylene and triethylene glycol in which additional Cd was sorbed to the soil from the soil solution. Additional Zn was sorbed in all columns tested with the exception of the Canelo I column perfused with ethyl alcohol.
• Zhang, Y., & Miller, R. M. (1992). Enhanced octadecane dispersion and biodegradation by a Pseudomonas rhamnolipid surfactant (biosurfactant). Applied and Environmental Microbiology, 58(10), 3276-3282.
  More info

  PMID: 1444363;PMCID: PMC183091;Abstract: A microbial surfactant (biosurfactant) was investigated for its potential to enhance bioavailability and, hence, the biodegradation of octadecane. The rhamnolipid biosurfactant used in this study was extracted from culture supernatants after growth of Pseudomonas aeruginosa ATCC 9027 in phosphate- limited proteose peptone-glucose-ammonium salts medium. Dispersion of octadecane in aqueous solutions was dramatically enhanced by 300 mg of the rhamnolipid biosurfactant per liter, increasing by a factor of more than 4 orders of magnitude, from 0.009 to >250 mg/liter. The relative enhancement of octadecane dispersion was much greater at low rhamnolipid concentrations than at high concentrations. Rhamnolipid-enhanced octadecane dispersion was found to be dependent on pH and shaking speed. Biodegradation experiments done with an initial octadecane concentration of 1,500 mg/liter showed that 20% of the octadecane was mineralized in 84 h in the presence of 300 mg of rhamnolipid per liter, compared with only 5% octadecane mineralization when no surfactant was present. These results indicate that rhamnolipids may have potential for facilitating the bioremediation of sites contaminated with hydrocarbons having limited water solubility.
• Miller, R. M., Park, E., & Thomas, J. A. (1991). Reduction (dethiolation) of protein mixed-disulfides; distribution and specificity of dethiolating enzymes and N,N′-bis(2-chloroethyl)-N-nitrosourea inhibition of an NADPH-dependent cardiac dethiolase. Archives of Biochemistry and Biophysics, 287(1), 112-120.
  More info

  PMID: 1897987;Abstract: The S-thiolated proteins phosphorylase b (Phb) and carbonic anhydrase III (CAIII) were prepared with [3H]glutathione in a reaction initiated with diamide. These substrates were used to measure the rate of reduction (dethiolation) of protein mixed-disulfides by enzymes with properties similar to those of thioredoxin and glutaredoxin. This enzyme activity is termed a dethiolase since the identities of the enzymes are still unknown. The dethiolation of either S-[3H]glutathiolated Phb or S-[3 H]glutathiolated CAIII was employed in tissue assays and for study of two partially purified dethiolases from cardiac tissue. NADPH-dependent dethiolase activity was most abundant except in rat liver and muscle. Total dethiolase activity was approximately 10-fold higher in neutrophils, 3T3-L1 cells, and Escherichia coli than in other sources. Rat skeletal muscle had 3- to 4-fold higher dethiolase activity than rat heart or liver. These data indicate that protein dethiolase activity is ubiquitous and that normal expression of the two dethiolase activities varies considerably. A partially purified cardiac NADPH-dependent dethiolase acted on Phb approximately 1.5 times faster than CAIII, and a glutathione (GSH)-dependent dethiolase acted on Phb 3 times faster than CAIII. The Km for glutathione for the GSH-dependent dethiolase was 15 μm with Phb as substrate and 10 μm with CAIII. Thus, the GSH-dependent dethiolase is probably not affected by normal changes in the cardiac glutathione content (normally approximately 3 mm). Partially purified cardiac NADPH-dependent dethiolase was inactivated by BCNU (N,N′-bis(2-chloroethyl)-N-nitrosourea) and the GSH-dependent dethiolase was unaffected under similar conditions. In a soluble extract from bovine heart, 200 μm BCNU inhibited NADPH-dependent dethiolase by more than 60% but did not affect GSH-dependent activity. These results demonstrate that BCNU is a selective inhibitor of the NADPH-dependent dethiolase. © 1991.
• Miller, R. M., Sies, H., Park, E., & Thomas, J. A. (1990). Phosphorylase and creatine kinase modification by thiol-disulfide exchange and by xanthine oxidase-initiated S-thiolation. Archives of Biochemistry and Biophysics, 276(2), 355-363.
  More info

  PMID: 2106288;Abstract: The reaction of glycogen phosphorylase b and creatine kinase with glutathione disulfide, cystine, and cystamine was compared by direct analysis on electrofocusing gels. This method was useful for individual proteins or for mixtures of the proteins. Millimolar concentrations of glutathione disulfide were required for both proteins and the rate of modification of each protein was similar. The reaction of glutathione disulfide with creatine kinase was inhibited by reduced glutathione (GSH), but the effect on the reaction with phosphorylase was minimal. Cystine and cystamine were required in micromolar amounts to effectively form the disulfide adducts. Both proteins were modified by cystine but cystamine reacted only with phosphorylase. Cystamine (10 μm) was an effective inhibitor of the reaction of phosphorylase b with 2 mm glutathione disulfide. S-thiolation of creatine kinase inactivated the enzyme and a direct assay of the enzyme activity could be used to quantitate S-thiolation of this protein by each of the disulfides. The effect of each disulfide on enzyme activity confirmed the results obtained by gel electrofocusing. Glutathione disulfide and cystine both inactivated the enzyme while cystamine had no effect on the activity. S-thiolation of phosphorylase had no observable effect on any activity parameter, but it effectively prevented binding of phosphorylase to high-molecular-weight glycogen, probably at the glycogen storage site of phosphorylase. The rate of S-thiolation of a mixture of phosphorylase and creatine kinase by thiol-disulfide exchange with glutathione disulfide was compared to the rate of S-thiolation of these proteins by a xanthine oxidase-initiated process (presumably due to protein sulfhydryl activation by reactive oxygen species). The xanthine oxidase-initiated mechanism was somewhat faster than thiol-disulfide exchange with both proteins. It was shown that GSH inhibited S-thiolation of creatine kinase by this mechanism as well as by thiol-disulfide exchange. It is suggested that both mechanisms may play a role in protein S-thiolation in vivo. For proteins that are typified by creatine kinase, the concentration of GSH in the cells may determine whether the S-thiolated form of the protein accumulates. For proteins typified by phosphorylase b, the accumulation of S-thiolated forms may be more independent of GSH. © 1990.
• Miller, R. M. (1988). Sequential degradation of chlorophenols by photolytic and microbial treatment. Environmental Science and Technology, 22(10), 1215-1219.
  More info

  Abstract: Using the radiolabeled model pollutants 2,4-dichlorophenol (DCP) and 2,4,5-trichlorophenol (TCP) we demonstrated that brief UV (300-nm) photolysis greatly facilitates the removal of the two chlorophenols from sewage through accelerated mineralization and binding of polar products. The addition of 0.1 M H2O2 strongly accelerated the photolysis process resulting in half-lives of 1.68 and 0.87 min for DCP and TCP, respectively. In natural sunlight, half-lives of the chlorophenols were less than 1 day when H2O2 was present. During 4 days of incubation in activated sewage sludge, only 3% of unphotolyzed DCP and 1 % of unphotolyzed TCP were mineralized. Mineralization rose to 79 and 59%, respectively, after photolysis in the presence of H2O2. Photolysis without H2O2 resulted in removal of chlorophenols from solution chiefly by binding. Increased mineralization and binding were observed also upon incubation of photolyzed chlorophenols in soil. Disruption of carbon-halogen bonds by brief photolysis followed by traditional biological effluent treatment offers an alternative to activated charcoal treatment for removal of xenobiotics from industrial effluents. © 1988 American Chemical Society.
• Miller, R. M., Singer, G. M., Rosen, J. D., & Bartha, R. (1988). Photolysis primes biodegradation of benzo[a]pyrene. Applied and Environmental Microbiology, 54(7), 1724-1730.
  More info

  PMID: 3415236;PMCID: PMC202736;Abstract: 14C-labeled benzo[a]pyrene (BaP) was used as a model compound for polycyclic aromatic hydrocarbons (PAH) in order to assess the effect of photolytic pretreatment on the subsequent fate of BaP in sewage sludge and soil test systems. Photolysis was performed in methanolic solution with or without 0.1 M H2O2, under either UV light (300 nm) or natural sunlight. The presence of H2O2 greatly enhanced the rate of photolysis both with UV and with natural sunlight. Intact BaP resisted biodegradation in both test systems. Photolysis transformed BaP to polar materials that were subject to increased mineralization and binding in both biological test systems. As shown by the Ames assay, photolysis decreased the mutagenicity of BaP to test strains TA98 and TA104 only moderately. The photolysate had an increased acute toxicity and lost its need for activation by S-9 enzymes. However, during subsequent incubation in soil or sewage sludge, mutagenicity decreased rapidly by one to two orders of magnitude and acute toxicity disappeared due to the mineralization and binding of photoproducts to humic materials. Photolysis of BaP and similar PAH compounds represents a useful treatment option that could be applied to certain PAH-containing petroleum refinery sludge and to coal tar residues in order to facilitate their detoxification and environmentally safe disposal.

Proceedings Publications

• Chief, K., Koch, C. L., Maier, R. M., Maracle, T., Rader, S., & Stanley, J. (2014, February). Mining and environmental educational modules for Tribal Colleges. In Annual Society for Mining, Metallurgy, and Exploration.
• Chief, K., Maier, R. M., Koch, C., Rader, S., & Maracle, T. (2014, February). Mining and Environmental Educational Modules for Tribal Community Colleges and Universities. In The Society for Mining, Metallurgy, and Exploration (SME) Annual Meeting & Exhibit “Leadership in Uncertain Times”, February 23 - 26, 2014, 5.
• Chief, K. -., Koch, C. L., Maier, R. M., Rader, S., Maracle, T., Chief, K. -., Koch, C. L., Maier, R. M., Rader, S., & Maracle, T. (2013, Fall). Mining and Environmental Educational Modules for Tribal Community Colleges and Universities. In The Society for Mining, Metallurgy, and Exploration (SME) Annual Meeting & Exhibit “Leadership in Uncertain Times”, February 23 - 26, 2014, Salt Lake City, UT.
• Chief, K., Maier, R. M., Koch, C., Maracle, T., & Rader, S. (2013, February). Mining and Environmental Educational Modules for Tribal Community Colleges and Universities. In Society for Mining, Metallurgy, and Exploration (SME) Annual Meeting & Exhibit “Leadership in Uncertain Times” February 23 - 26, 2014, 5.

Presentations

• Amy, G., Maier, R. M., Crittenden, J., Thomas, V., Hogan, D. E., & Dale, M. (2022). A new paradigm for the mining industry: recovery of valuable metals from saline aqueous sources. Singapore International Water Week Water Convention.
• Hogan, D. E., & Maier, R. M. (2022). A New Paradigm for Metal Cleanup and Mining: Recovery from Saline Aqueous Sources. Environmental Protection Agency Technical Assessment Branch.
• Maier, R. M. (2021, February). Invited presentation: The mine tailings microbiome – friend or foe of revegetation?. Massachusetts Institute of Technology. virtual.
• Maier, R. M. (2021, January). Invited presenation: Revegetation of mine wastes: lessons learned and stakeholder communication. Montana Tech University Public Lecture Series. virtual.
• Maier, R. M. (2021, November). Keynote Presentation: Revegetation of mine wastes: lessons learned and stakeholder communication. V International Symposium on Microbiology and Biotechnology. virtual.
• Maier, R. M. (2020, yearlong). Invited and Submitted Presentations. see attached.
  More info

  see attached list of presentations
• Maier, R. M. (2019, full year). 10 invited presentations - detailed in attached file. invited presentations.
• Maier, R. M. (2019, full year). 12 submitted abstracts and presentations detailed in the attached file. submitted presentations.
• Maier, R. M. (2017, 2017). Invited Presentations (9). Local/National/International.
• Maier, R. M. (2017, 2017). Submitted presentations (18). Local/National/International.
• Eismin, R. J., Palos Pacheco, R., Munusamy, E., Hogan, D. E., Maier, R. M., Polt, R. L., Schwartz, S. D., & Pemberton, J. E. (2016, Summer). Microenvironment of Monorhamnolipid Aggregates and their Synthetically Produced Diastereomers as a Function of Solution Conditions. 252nd American Chemical Society National Meeting & Exposition. Philadelphia, PA: American Chemical Society.
• Fathi, S. A., Maier, R. M., & Pemberton, J. E. (2016, Summer). Synthesis, characterization, and heavy metal binding properties of new sugar-based glycolipid surfactants. 252nd American Chemical Society National Meeting & Exposition. Philadelphia, PA: American Chemical Society.
• Maier, R. M. (2016, Jan - Dec). Invited Presentations (9). Local/National/International.
• Maier, R. M. (2016, Jan - Dec). Submitted Presentations (16). Local/National/International.
• Chief, K., Maier, R. M., Moreno, D., & Wilkinson, S. T. (2015, January 2015). Tribal Mining and Environmental Educational Modules. CDC Information Meeting about Arsenic. North Komelik Village, AZ: Tohono O’odham Nation.
  More info

  Chief, K., R. Maier, D. Moreno, and S.T. Wilkinson. 2015. Tribal Mining and Environmental Educational Modules, January 14, 2015, N. Komelik Village, Tohono O’odham Nation, AZ.
• Dontsova, K. M., Huxman, T. E., Chorover, J. D., Maier, R. M., Zaharescu, G. D., & Burghelea, C. (2015, November). Grass and microbiota effect on lithogenic element mobilization during weathering of basalt, granite, rhyolite, and schist. Geological Society of America annual meeting. Baltimore, MD: Geological Society of America.
• Dontsova, K. M., Zaharescu, G. D., Burghelea, C., Chorover, J. D., Maier, R. M., & Huxman, T. E. (2015, July). Nutrient mobilization during biological weathering. Frontiers in Experimental Ecosystem Science. Paris, France: CNRS, ENS.
• Eismin, R. J., Palos-Pacheco, R., Coss, C. S., Polt, R. L., Maier, R. M., & Pemberton, J. E. (2015, Spring). Aggregation Characteristics of Rhamnolipid Biosurfactants and Their Synthetic Variants. 106th Annual Meeting of the American Oil Chemists Society. Orlando, FL: Americanb Oil Chemists Society.
• Maier, R. M. (2015, 2015). 11 invited presentations. see attached.
• Maier, R. M. (2015, 2015). 17 submitted presentations (abstracts). see attached.
• Chief, K., Maier, R. M., & Sierra, R. (2014, May). Mining and Environmental Educational Modules for Tribal Colleges. 9th Biennial Association of Natural Resources Extension Professionals Conference, May 18-22, 2014. Sacramento, CA.: Natural Resources Extension Professionals.
  More info

  Chief, K., R. Maier, M. Poulton, and R. Sierra. 2014. Mining and Environmental Educational Modules for Tribal Colleges. 9th Biennial Association of Natural Resources Extension Professionals Conference, May 18-22, 2014, Sacramento, CA.
• Maier, R. M. (2014, see attached). 10 submitted presentations, see attached. see attached.
• Maier, R. M. (2014, see attached). 12 Invited presentations, see attached. see attached.
• Koch, C. L., Chief, K. -., & Maier, R. M. (2013, Fall). Mining and Environmental Educational Modules for Tribal Community Colleges and Universities. American Indian Higher Education Consortium (AIHEC) First Americans Land-grant Consortium (FALCON) 9th Annual Conference. Washington, D.C.
• Maier, R. M. (2013, see attached). 13 Submitted Abstracts and Presentations (see attached). see attached.
• Maier, R. M. (2013, see attached). 4 Invited Presentations (see attached). see attached.

Poster Presentations

• Annie, M., Maier, R. M., & Hogan, D. E. (2022, November). Glycolipid Based Recovery of Metals and Rare Earth Elements. Applied Industry Research and Information Sharing Conference. Phoenix, AZ: UArizona Center for Environmentally Sustainable Mining.
• Perez, S., Hogan, D. E., Lokugama, V., Loy, D. A., Babst-Kostecka, A., & Maier, R. M. (2022, December). Conditional Stability Constants for Synthetically Derived Glycolipids. NIEHS Superfund Research Program Annual Meeting. Raleigh, NC: NIEHS.
• Perez, S., Hogan, D. E., Lokugama, V., Loy, D. A., Babst-Kostecka, A., & Maier, R. M. (2022, December). Conditional Stability Constants for Synthetically Derived Glycolipids. SME Arizona Conference. Tucson, AZ: Society for Mining, Metallurgy and Exploration.
• Annie, M., Maier, R. M., & Hogan, D. E. (2022, November). A glycolipid based non-traditional method of generating metals and rare earth elements from mining impacted waters. Arizona Conference. Tucson, AZ: Society for Mining, Metallurgy and Exploration.
• Fontana, C., Lauman, S., Ledesma, J., Kline, A., Gornish, E., Maier, R. M., & Neilson, J. W. (2021). Impact of hydroseeding season and AMF inoculation on belowground fertility indicators at an Arizona copper mine. Soil Science Society of America annual meeting.
• Kushwaha, P., Maier, R. M., Neilson, J. W., & Babst-Kostecka, A. (2020, November). Linking the rhizosphere microbial community with variability in Zn and Cd hyperaccumulation in the model species Arabidopsis halleri. 2020 ASA-CSSA-SSSA International Annual Meeting. Virtual.
• Danny, K., Maier, R. M., & Chief, K. (2017, October). Educational modules for mining-impacted tribal communities.. Tribal Environmental Health Sciences Forum. Wild Horse Pass Hotel & Resort, Chandler, AZ: 2017 University of Arizona, Southwest Environmental Health Science Center.
• Hanrahan, D. J., Palos-Pacheco, R., Jones, E. M., Szabo, L., Kegel, L. L., Maier, R. M., Pemberton, J. E., & Polt, R. L. (2015, Spring). Synthesis and Structure-Function Relationships of Glycolipid Surfactants. LIPID MAPS Annual Meeting 2015. La Jolla, CA.
• Hogan, D. E., Palos-Pacheco, R., Polt, R. L., Pemberton, J. E., & Maier, R. M. (2015, Spring). Biosurfactants as a Tool for Metal Removal from Waste Effluents. 249th American Chemical Society National Meeting & Exposition. Denver, CO.

Other Teaching Materials

• Jennifer, S., Wilkinson, S. T., Moreno Ramirez, D., Maier, R. M., & Chief, K. (2015. Tribal Mining Educational Modules: Copper Mining and Processing. University of Arizona.

Others

• Artiola, J. F., Chief, K., Beamer, P., Wilkinson, S. T., Maier, R. M., Rock, C. M., & Sanchez, C. A. (2016, April). The Gold King Mine Spill: Can it Impact Water Users below Lake Powell Reservoir and Yuma Farmers?. University of Arizona, College of Agriculture & Life Sciences, Cooperative Extension. http://arizona.openrepository.com/arizona/bitstream/10150/607717/1/az1698-2016.pdf
• Lantz, R. C., Chief, K., & Maier, R. M. (2016, April). University of Arizona programs on environmental health and mining impacts in native populations. "University of Arizona programs on environmental health and mining impacts in native populations" written and oral testimony provided to a Senate field hearing (chaired by Senators Barrasso and McCain): “Examining EPA’s Unacceptable Response to Indian Tribes”. City of Phoenix Council Chambers, Phoenix, AZ,.
• Maier, R. M. (2016, April). An Emerging Diverse Workforce to Reclaim Abandoned Mine Lands; Increasing Hispanic Participation. "An Emerging Diverse Workforce to Reclaim Abandoned Mine Lands; Increasing Hispanic Participation" provided written and oral testimony in a Capitol Hill Policy Briefing Series hosted by the Congressional Hispanic Caucus Institute, Washington DC.
• Maier, R. M. (2016, July/Aug). Not just dust.. "Not just dust" a media interview for Desert Leaf the Catalina Foothills Magazine. http://trendmag2.trendoffset.com/publication/?m=12024&l=1
  More info

  Media Interview
• Maier, R. M. (2016, May). The role of microorganisms in making life livable on planet Earth. "The role of microorganisms in making life livable on planet Earth" interview for Arizona Public Media, Arizona Science. https://radio.azpm.org/arizonascience/
• Maier, R. M., & Chief, K. (2016, August). Is mine waste spill threatening Arizona’s water?. "Is mine waste spill threatening Arizona’s water?" interview for Arizona Public Media, AZ Week. https://www.azpm.org/s/33103-az-week-pollution-from-colorado-mine-spill-flows-toward-arizona/
• Chief, K., Artiola, J. F., Beamer, P., Wilkinson, S. T., Maier, R. M., Rock, C. M., & Sanchez, C. A. (2015, August). Understanding the Gold King Mine Spill. CALS publications Website. http://superfund.pharmacy.arizona.edu/info-material/gold-king-mine
  More info

  This bulletin was produced in response to questions arising about the Gold King Mine spill.
• Chief, K., Chief, K., Artiola, J. F., Artiola, J. F., Beamer, P., Beamer, P., Wilkinson, S. T., Wilkinson, S. T., Maier, R. M., Maier, R. M., Rock, C. M., Rock, C. M., Sanchez, C. A., & Sanchez, C. A. (2015, August). Understanding the Gold King Mine Spill. web. http://superfund.pharmacy.arizona.edu/info-material/gold-king-mine
  More info

  This bulletin was produced in response to questions arising about the Gold King Mine spill.
• Maier, R. M. (2015, April). Company finds intersection of research, commerce, environmental benefits. Arizona Daily Star. http://tucson.com/business/local/company-finds-intersection-of-research-commerce-environmental-benefits/article_61ba1f73-ce1a-59be-9d62-528a892c8cc5.html
• Maier, R. M. (2015, April). What about Earth’s Microbiome?. Scientific American invited guest blog. http://blogs.scientificamerican.com/guest-blog/2015/04/22/what-about-earths-microbiome/
• Maier, R. M., & Chief, K. (2015, August). Is mine waste spill threatening Arizona’s water?. Arizona Public Media, AZ Week. https://www.azpm.org/s/33103-az-week-pollution-from-colorado-mine-spill-flows-toward-arizona/
  More info

  https://www.azpm.org/s/33103-az-week-pollution-from-colorado-mine-spill-flows-toward-arizona/
• Pemberton, J. E., & Maier, R. M. (2015, August). Surfactants: building greener chemicals. NSF Science Nation. http://www.nsf.gov/news/special_reports/science_nation/surfactants.jsp