Raina Margaret Maier

Raina Margaret Maier

Professor, Environmental Science
Professor, Pharmaceutical Sciences
Professor, Pharmacology and Toxicology
Professor, BIO5 Institute
Primary Department
Department Affiliations
Contact
(520) 621-7231

Research Interest

Raina M Maier, PhD, is a Professor of Environmental Microbiology in the Department of Soil, Water and Environmental Science and Director of the University of Arizona NIEHS Superfund Research Program. She also serves as Director of the University of Arizona Center for Environmentally Sustainable Mining and as Deputy Director of the TRIF Water Sustainability Program. Dr. Maier is internationally known for her work on microbial surfactants (biosurfactants) including discovery of a new class of biosurfactants and of novel applications for these unique materials in remediation and green technologies. She is also recognized for her work on the relationships between microbial diversity and ecosystem function in oligotrophic environments such as carbonate caves, the Atacama desert, and mine tailings. Dr. Maier has published over 100 original research papers, authored 23 book chapters, and holds a patent on the use of biosurfactants to control zoosporic plant pathogens. She is the lead author on the textbook “Environmental Microbiology” currently in its second edition.Dr. Maier emphasizes a multidisciplinary approach to her work and has served as PI or co-PI on several large granting efforts including the UA NIEHS Superfund Research Program, the UA NSF Kartchner Caverns Microbial Observatory, and the UA NSF Collaborative Research in Chemistry grant on biosurfactants.

Publications

Maslin, P., & Maier, R. M. (2000). Rhamnolipid-enhanced mineralization of phenanthrene in organic-metal co-contaminated soils. Bioremediation Journal, 4(4), 295-308.

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.

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.

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.

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.

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.

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.

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.

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.

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.