About

Tamar Barkay is an Emeritus Distinguished Professor in the Department of Biochemistry and Microbiology at Rutgers University. Her research focuses on the microbial ecology of interactions between microbes and toxic metals, specifically microbial transformations of metals and their effects on metal toxicity and accumulation in the environment. Her work investigates the genetics and physiology of metal resistance and transformations in bacteria, supporting efforts in bioremediation of metal-contaminated environments. Her ongoing research projects include studying the role of microbes in the formation and accumulation of methylmercury in aquatic environments, which is the most toxic form of mercury that biomagnifies in the food chain, posing risks to predators including humans. She also examines the role of horizontal gene transfer among bacteria in the spread of mercury and antibiotics resistance genes, which may lead to the development of resistance gene pools in contaminated environments. Her research heavily relies on molecular tools such as cloning, gene probing, mRNA transcript analysis, metagenomics, and metatranscriptomics in microbial ecology.

Research topics

• Biology
• Genetics
• Computer Science
• Chemistry
• Environmental chemistry
• Evolutionary biology
• Programming language
• Biochemistry

Selected publications

• Microbial mercury transformations: Molecules, functions and organisms

  Advances in applied microbiology · 2022 · 38 citations

  Senior authorCorresponding
  • Environmental chemistry
  • Biology
  • Chemistry
  PublisherDOI

• Nutrient Inputs Stimulate Mercury Methylation by Syntrophs in a Subarctic Peatland

  Frontiers in Microbiology · 2021-10-04 · 24 citations

  articleOpen accessSenior author

  Climate change dramatically impacts Arctic and subarctic regions, inducing shifts in wetland nutrient regimes as a consequence of thawing permafrost. Altered hydrological regimes may drive changes in the dynamics of microbial mercury (Hg) methylation and bioavailability. Important knowledge gaps remain on the contribution of specific microbial groups to methylmercury (MeHg) production in wetlands of various trophic status. Here, we measured aqueous chemistry, potential methylation rates (k meth ), volatile fatty acid (VFA) dynamics in peat-soil incubations, and genetic potential for Hg methylation across a groundwater-driven nutrient gradient in an interior Alaskan fen. We tested the hypotheses that (1) nutrient inputs will result in increased methylation potentials, and (2) syntrophic interactions contribute to methylation in subarctic wetlands. We observed that concentrations of nutrients, total Hg, and MeHg, abundance of hgcA genes, and rates of methylation in peat incubations (k meth ) were highest near the groundwater input and declined downgradient. hgcA sequences near the input were closely related to those from sulfate-reducing bacteria (SRB), methanogens, and syntrophs. Hg methylation in peat incubations collected near the input source (FPF2) were impacted by the addition of sulfate and some metabolic inhibitors while those down-gradient (FPF5) were not. Sulfate amendment to FPF2 incubations had higher k meth relative to unamended controls despite no effect on k meth from addition of the sulfate reduction inhibitor molybdate. The addition of the methanogenic inhibitor BES (25 mM) led to the accumulation of VFAs, but unlike molybdate, it did not affect Hg methylation rates. Rather, the concurrent additions of BES and molybdate significantly decreased k meth , suggesting a role for interactions between SRB and methanogens in Hg methylation. The reduction in k meth with combined addition of BES and molybdate, and accumulation of VFA in peat incubations containing BES, and a high abundance of syntroph-related hgcA sequences in peat metagenomes provide evidence for MeHg production by microorganisms growing in syntrophy. Collectively the results suggest that wetland nutrient regimes influence the activity of Hg methylating microorganisms and, consequently, Hg methylation rates. Our results provide key information about microbial Hg methylation and methylating communities under nutrient conditions that are expected to become more common as permafrost soils thaw.

  PublisherDOI

• Expanded Diversity and Phylogeny of mer Genes Broadens Mercury Resistance Paradigms and Reveals an Origin for MerA Among Thermophilic Archaea

  Frontiers in Microbiology · 2021 · 83 citations

  • Biology
  • Genetics
  • Evolutionary biology

  -encoded functionalities, and suggest that selection for Hg(II) and MeHg detoxification is dependent not only on the availability and type of mercury compounds in the environment but also the physiological potential of the microbes who inhabit these environments. The expanded diversity and environmental distribution of MerAB identify new targets to prioritize for future research.

  PublisherDOI

• Demethylation─The Other Side of the Mercury Methylation Coin: A Critical Review

  ACS Environmental Au · 2021 · 134 citations

  1st authorCorresponding
  • Computer Science
  • Computer Science
  • Chemistry

  -independent oxidative demethylation, likely involving some strains of anaerobic bacteria as well as aerobic methane-oxidizing bacteria, i.e., methanotrophs. In addition, photochemical and chemical demethylation processes are described, including the roles of dissolved organic matter (DOM) and free radicals as well as dark abiotic demethylation in the natural environment about which little is currently known. We focus on mechanisms and processes of demethylation and highlight the uncertainties and known effects of environmental factors leading to MeHg degradation. Finally, we suggest future research directions to further elucidate the chemical and biochemical mechanisms of biotic and abiotic demethylation and their significance in controlling net MeHg production in natural ecosystems.

  PublisherDOI

• Expression and regulation of the <i>mer</i> operon in <i>Thermus thermophilus</i>

  Environmental Microbiology · 2020-02-23 · 14 citations

  articleSenior authorCorresponding

  Summary Mercury (Hg) is a highly toxic and widely distributed heavy metal, which some Bacteria and Archaea detoxify by the reduction of ionic Hg (Hg[II]) to the elemental volatile form, Hg(0). This activity is specified by the mer operon. The mer operon of the deeply branching thermophile Thermus thermophilus HB27 encodes for, an O ‐acetyl‐ l ‐homoacetylserine sulfhydrylase (Oah2), a transcriptional regulator (MerR), a hypothetical protein (hp) and a mercuric reductase (MerA). Here, we show that this operon has two convergently expressed and differentially regulated promoters. An upstream promoter, P oah , controls the constitutive transcription of the entire operon and a second promoter (P mer ), located within merR , is responsive to Hg(II). In the absence of Hg(II), the transcription of merA is basal and when Hg(II) is present, merA transcription is induced. This response to Hg(II) is controlled by MerR and genetic evidence suggests that MerR acts as a repressor and activator of P mer . When the whole merR , including P mer , is removed, merA is transcribed from P oah independently of Hg(II). These results suggest that the transcriptional regulation of mer in T . thermophilus is both similar to, and different from, the well‐documented regulation of proteobacterial mer systems, possibly representing an early step in the evolution of mer ‐operon regulation.

  PublisherDOI

• Tagging the vanA gene in wastewater microbial communities for cell sorting and taxonomy of vanA carrying cells

  The Science of The Total Environment · 2020-05-06 · 6 citations

  article
  PublisherDOI

• Characterizing and Evaluating the Diverse Microbial Communities and Their Mercury Resistance Potential from Hot Spring Sites Representing Gradients in Temperature and pH in Yellowstone National Park

  Aresty Rutgers Undergraduate Research Journal · 2020-12-21

  articleOpen accessSenior author

  Yellowstone National Park is home to many different hot springs, lakes, geysers, pools, and basins that range in pH, chemical composition, and temperature. These different environmental variations provide a broad range of conditions that select and grow diverse communities of microorganisms. In this study, we collected samples from geochemically diverse lakes and springs to characterize the microbial communities present through 16S rRNA metagenomic analysis. This information was then used to observe how various microorganisms survive in high mercury environments. The results show the presence of microorganisms that have been studied in previous literature. The results also depict gradients of microorganisms including thermophilic bacteria and archaea that exist in these extreme environments. In addition, beta diversity analyses of the sequence data showed site clustering based primarily on temperature instead of pH or sample site, suggesting that while pH, temperature, and sample site were all shown to be significant, temperature is the strongest factor driving microorganism community development. While it is important to characterize the microorganism community present, it is also important to understand how this community functions as a result of its selection. Along with looking at community composition, genomic material was tested to see if it contained mercury methylating (hgcA) or mercury reducing (merA) genes. Out of 22 samples, three of them were observed to have merA genes, while no samples had hgcA genes. These results indicate that microorganisms in Mustard and Nymph Springs may use mercury reduction. Understanding how microorganisms survive in environments with high concentrations of toxic pollutants is crucial because it can be used as a model to better understand mechanisms of resistance and the biogeochemical cycle, as well as for bioremediation and other solutions to anthropogenic problems.

  PublisherOA PDFDOI

• Toxicity Testing in Soil Using Microorganisms

  2019-07-23 · 7 citations

  book-chapter1st authorCorresponding

  The potential toxicity of xenobiotics to bacteria in agricultural soils has implications for land management and farm production. Metabolic processes which are utilized in toxicity measurements include nutrient cycling, enzyme activities, sulfur oxidation, and quantifications of adenosine triphosphate and biomass. The use of endogenous soil microbes as biological instruments in toxicant assessment has been discussed. The undisturbed cycling of carbon in the soil milieu is a major factor in the maintenance of soil productivity, but the use of this cycle as a measurement of soil microbial activity is still a controversial issue. The movement of nitrogen through the environment is mediated by the metabolic activities of microorganisms. Four processes within the nitrogen cycle are paramount in their dependence on microorganisms: ammonification, nitrification, denitrification, and nitrogen fixation. The validity of the bioassay to produce a fingerprint of the metals which are present in the soil in elevated concentrations was assessed using various metal extractants.

  PublisherDOI

• Genome-facilitated discovery of RND efflux pump-mediated resistance to cephalosporins in Vibrio spp. isolated from the mummichog fish gut

  Journal of Global Antimicrobial Resistance · 2019-05-14 · 14 citations

  articleOpen accessSenior author
  PublisherOA PDFDOI

• Superoxide Dismutase and Pseudocatalase Increase Tolerance to Hg(II) in Thermus thermophilus HB27 by Maintaining the Reduced Bacillithiol Pool

  mBio · 2019-04-01 · 18 citations

  articleOpen access

  Thermus thermophilus is a deep-branching thermophilic aerobe. It is a member of the Deinococcus - Thermus phylum that, together with the Aquificae , constitute the earliest branching aerobic bacterial lineages; therefore, this organism serves as a model for early diverged bacteria (R. K. Hartmann, J. Wolters, B. Kröger, S. Schultze, et al., Syst Appl Microbiol 11:243–249, 1989, https://doi.org/10.1016/S0723-2020(89)80020-7 ) whose natural heated habitat may contain mercury of geological origins (G. G. Geesey, T. Barkay, and S. King, Sci Total Environ 569-570:321–331, 2016, https://doi.org/10.1016/j.scitotenv.2016.06.080 ). T. thermophilus likely arose shortly after the oxidation of the biosphere 2.4 billion years ago. Studying T. thermophilus physiology provides clues about the origin and evolution of mechanisms for mercury and oxidative stress responses, the latter being critical for the survival and function of all extant aerobes.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Effects of Trophic Status Alterations on Pathways of Mercury Methylation in Northern Wetlands

  NSF · $385k · 2013–2018

• Collaborative Research: Mercury isotope fractionation during microbial and abiotic redox transformations

  NSF · $237k · 2004–2009

Frequent coauthors

• Alexandre J. Poulain

  19 shared

• Joel D. Blum

  University of Michigan–Ann Arbor

  18 shared

• Marc Amyot

  Center for Northern Studies

  18 shared

• John R. Reinfelder

  Rutgers, The State University of New Jersey

  17 shared

• Ralph R. Turner

  West Virginia University

  15 shared

• Jeffra K. Schaefer

  Rutgers, The State University of New Jersey

  15 shared

• K. Kritee

  14 shared

• Nathan Yee

  Rutgers, The State University of New Jersey

  14 shared

Labs

• American Society for Microbiology Student Chapter at RutgersPI