157 results on '"Tamar Barkay"'
Search Results
2. Nutrient Inputs Stimulate Mercury Methylation by Syntrophs in a Subarctic Peatland
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Spencer Roth, Brett A. Poulin, Zofia Baumann, Xiao Liu, Lin Zhang, David P. Krabbenhoft, Mark E. Hines, Jeffra K. Schaefer, and Tamar Barkay
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climate change ,peatland ,hgcA ,syntrophy ,mercury methylation ,Microbiology ,QR1-502 - Abstract
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 (kmeth), 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 (kmeth) 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 kmeth relative to unamended controls despite no effect on kmeth 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 kmeth, suggesting a role for interactions between SRB and methanogens in Hg methylation. The reduction in kmeth 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.
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- 2021
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3. Expanded Diversity and Phylogeny of mer Genes Broadens Mercury Resistance Paradigms and Reveals an Origin for MerA Among Thermophilic Archaea
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Christos A. Christakis, Tamar Barkay, and Eric S. Boyd
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mercury ,methylmercury ,mercuric reductase ,organomercury lyase ,merA ,MerB ,Microbiology ,QR1-502 - Abstract
Mercury (Hg) is a highly toxic element due to its high affinity for protein sulfhydryl groups, which upon binding, can destabilize protein structure and decrease enzyme activity. Prokaryotes have evolved enzymatic mechanisms to detoxify inorganic Hg and organic Hg (e.g., MeHg) through the activities of mercuric reductase (MerA) and organomercury lyase (MerB), respectively. Here, the taxonomic distribution and evolution of MerAB was examined in 84,032 archaeal and bacterial genomes, metagenome assembled genomes, and single-cell genomes. Homologs of MerA and MerB were identified in 7.8 and 2.1% percent of genomes, respectively. MerA was identified in the genomes of 10 archaeal and 28 bacterial phyla previously unknown to code for this functionality. Likewise, MerB was identified in 2 archaeal and 11 bacterial phyla previously unknown to encode this functionality. Surprisingly, homologs of MerB were identified in a number of genomes (∼50% of all MerB-encoding genomes) that did not encode MerA, suggesting alternative mechanisms to detoxify Hg(II) once it is generated in the cytoplasm. Phylogenetic reconstruction of MerA place its origin in thermophilic Thermoprotei (Crenarchaeota), consistent with high levels of Hg(II) in geothermal environments, the natural habitat of this archaeal class. MerB appears to have been recruited to the mer operon relatively recently and likely among a mesophilic ancestor of Euryarchaeota and Thaumarchaeota. This is consistent with the functional dependence of MerB on MerA and the widespread distribution of mesophilic microorganisms that methylate Hg(II) at lower temperature. Collectively, these results expand the taxonomic and ecological distribution of mer-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.
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- 2021
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4. Mercury affects the phylloplane fungal community of blueberry leaves to a lesser extent than plant age
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Katalin Malcolm, John Dighton, and Tamar Barkay
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Phylloplane fungi ,mercury ,heavy metal ,community ,pollution ,Biology (General) ,QH301-705.5 ,Microbiology ,QR1-502 - Abstract
Mercury (Hg) is a toxic heavy metal pollutant that is globally distributed due to atmospheric deposition to non-point source locations. Leaf surfaces directly sequester atmospheric Hg. Little is known of how phylloplane (leaf surface) fungi are influenced by Hg pollution. Through culture-based methodology, this study analysed fungal phylloplane community identity following a single-dose response to HgCl2 concentrations between 0 and 20 times ambient levels for New Jersey. Time passed following the Hg addition had a strong influence on the fungal phylloplane community, associated with natural successional changes. Mercury, however, did not significantly affect the phylloplane community identity. Notably, the control group was not significantly different than any of the Hg treatments. How the phylloplane functional group responds to Hg pollution has not been previously investigated and more research is needed to fully understand how Hg influences fungal phylloplane ecology.
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- 2018
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5. Superoxide Dismutase and Pseudocatalase Increase Tolerance to Hg(II) in Thermus thermophilus HB27 by Maintaining the Reduced Bacillithiol Pool
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Javiera Norambuena, Thomas E. Hanson, Tamar Barkay, and Jeffrey M. Boyd
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Thermus thermophilus ,bacillithiol ,iron ,mercury ,pseudocatalase ,reactive oxygen species ,Microbiology ,QR1-502 - Abstract
ABSTRACT Mercury (Hg) is a widely distributed, toxic heavy metal with no known cellular role. Mercury toxicity has been linked to the production of reactive oxygen species (ROS), but Hg does not directly perform redox chemistry with oxygen. How exposure to the ionic form, Hg(II), generates ROS is unknown. Exposure of Thermus thermophilus to Hg(II) triggered ROS accumulation and increased transcription and activity of superoxide dismutase (Sod) and pseudocatalase (Pcat); however, Hg(II) inactivated Sod and Pcat. Strains lacking Sod or Pcat had increased oxidized bacillithiol (BSH) levels and were more sensitive to Hg(II) than the wild type. The ΔbshA Δsod and ΔbshA Δpcat double mutant strains were as sensitive to Hg(II) as the ΔbshA strain that lacks bacillithiol, suggesting that the increased sensitivity to Hg(II) in the Δsod and Δpcat mutant strains is due to a decrease of reduced BSH. Treatment of T. thermophilus with Hg(II) decreased aconitase activity and increased the intracellular concentration of free Fe, and these phenotypes were exacerbated in Δsod and Δpcat mutant strains. Treatment with Hg(II) also increased DNA damage. We conclude that sequestration of the redox buffering thiol BSH by Hg(II), in conjunction with direct inactivation of ROS-scavenging enzymes, impairs the ability of T. thermophilus to effectively metabolize ROS generated as a normal consequence of growth in aerobic environments. IMPORTANCE 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.
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- 2019
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6. Some like it cold: microbial transformations of mercury in polar regions
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Niels Kroer, Alexandre J. Poulain, and Tamar Barkay
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Microbiology ,mercury biogeochemistry ,redox transformations ,polar regions ,methylation ,Environmental sciences ,GE1-350 ,Oceanography ,GC1-1581 - Abstract
The contamination of polar regions with mercury that is transported from lower latitudes as inorganic mercury has resulted in the accumulation of methylmercury (MeHg) in food chains, risking the health of humans and wildlife. While production of MeHg has been documented in polar marine and terrestrial environments, little is known about the responsible transformations and transport pathways and the processes that control them. We posit that as in temperate environments, microbial transformations play a key role in mercury geochemical cycling in polar regions by: (1) methylating mercury by one of four proposed pathways, some not previously described; (2) degrading MeHg by activities of mercury resistant and other bacteria; and (3) carrying out redox transformations that control the supply of the mercuric ion, the substrate of methylation reactions. Recent analyses have identified a high potential for mercury-resistant microbes that express the enzyme mercuric reductase to affect the production of gaseous elemental mercury when and where daylight is limited. The integration of microbially mediated processes in the paradigms that describe mercury geochemical cycling is therefore of high priority especially in light of concerns regarding the effect of global warming and permafrost thawing on input of MeHg to polar regions.
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- 2011
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7. The Use of a Mercury Biosensor to Evaluate the Bioavailability of Mercury-Thiol Complexes and Mechanisms of Mercury Uptake in Bacteria.
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Udonna Ndu, Tamar Barkay, Robert P Mason, Amina Traore Schartup, Radwan Al-Farawati, Jie Liu, and John R Reinfelder
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Medicine ,Science - Abstract
As mercury (Hg) biosensors are sensitive to only intracellular Hg, they are useful in the investigation of Hg uptake mechanisms and the effects of speciation on Hg bioavailability to microbes. In this study, bacterial biosensors were used to evaluate the roles that several transporters such as the glutathione, cystine/cysteine, and Mer transporters play in the uptake of Hg from Hg-thiol complexes by comparing uptake rates in strains with functioning transport systems to strains where these transporters had been knocked out by deletion of key genes. The Hg uptake into the biosensors was quantified based on the intracellular conversion of inorganic mercury (Hg(II)) to elemental mercury (Hg(0)) by the enzyme MerA. It was found that uptake of Hg from Hg-cysteine (Hg(CYS)2) and Hg-glutathione (Hg(GSH)2) complexes occurred at the same rate as that of inorganic complexes of Hg(II) into Escherichia coli strains with and without intact Mer transport systems. However, higher rates of Hg uptake were observed in the strain with a functioning Mer transport system. These results demonstrate that thiol-bound Hg is bioavailable to E. coli and that this bioavailability is higher in Hg-resistant bacteria with a complete Mer system than in non-resistant strains. No difference in the uptake rate of Hg from Hg(GSH)2 was observed in E. coli strains with or without functioning glutathione transport systems. There was also no difference in uptake rates between a wildtype Bacillus subtilis strain with a functioning cystine/cysteine transport system, and a mutant strain where this transport system had been knocked out. These results cast doubt on the viability of the hypothesis that the entire Hg-thiol complex is taken up into the cell by a thiol transporter. It is more likely that the Hg in the Hg-thiol complex is transferred to a transport protein on the cell membrane and is subsequently internalized.
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- 2015
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8. Microbial mercury transformations: Molecules, functions and organisms
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Ri-Qing, Yu and Tamar, Barkay
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Humans ,Mercury ,Methylmercury Compounds ,Methylation ,Phylogeny - Abstract
Mercury (Hg) methylation, methylmercury (MeHg) demethylation, and inorganic redox transformations of Hg are microbe-mediating processes that determine the fate and cycling of Hg and MeHg in many environments, and by doing so influence the health of humans and wild life. The discovery of the Hg methylation genes, hgcAB, in the last decade together with advances in high throughput and genome sequencing methods, have resulted in an expanded appreciation of the diversity of Hg methylating microbes. This review aims to describe experimentally confirmed and recently discovered hgcAB gene-carrying Hg methylating microbes; phylogenetic and taxonomic analyses are presented. In addition, the current knowledge on transformation mechanisms, the organisms that carry them out, and the impact of environmental parameters on Hg methylation, MeHg demethylation, and inorganic Hg reduction and oxidation is summarized. This knowledge provides a foundation for future action toward mitigating the impact of environmental Hg pollution.
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- 2022
9. Microbial mercury transformations: Molecules, functions and organisms
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Ri-Qing Yu and Tamar Barkay
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- 2022
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10. Israel vs. BDS: corporate social responsibility and the politics of human rights
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Ronen Shamir and Tamar Barkay
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Public Administration ,Sociology and Political Science ,Human rights ,media_common.quotation_subject ,05 social sciences ,Geography, Planning and Development ,Management, Monitoring, Policy and Law ,Public administration ,050601 international relations ,0506 political science ,Politics ,Political science ,050602 political science & public administration ,Corporate social responsibility ,General Economics, Econometrics and Finance ,media_common - Abstract
This is a case-study of an organized Israeli effort to disengage the issue of corporations in the Palestinian Occupied Territories from the global CSR framework of human rights. At the centre of th...
- Published
- 2019
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11. Expanded Diversity and Phylogeny of mer Genes Broadens Mercury Resistance Paradigms and Reveals an Origin for MerA Among Thermophilic Archaea
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Eric S. Boyd, Christos A. Christakis, and Tamar Barkay
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Microbiology (medical) ,Genetics ,0303 health sciences ,Thaumarchaeota ,mercury ,biology ,030306 microbiology ,MerB ,methylmercury ,Bacterial genome size ,mercuric reductase ,biology.organism_classification ,Genome ,Microbiology ,QR1-502 ,03 medical and health sciences ,Crenarchaeota ,Phylogenetics ,Metagenomics ,merA ,organomercury lyase ,Euryarchaeota ,030304 developmental biology ,Archaea - Abstract
Mercury (Hg) is a highly toxic element due to its high affinity for protein sulfhydryl groups, which upon binding, can destabilize protein structure and decrease enzyme activity. Prokaryotes have evolved enzymatic mechanisms to detoxify inorganic Hg and organic Hg (e.g., MeHg) through the activities of mercuric reductase (MerA) and organomercury lyase (MerB), respectively. Here, the taxonomic distribution and evolution of MerAB was examined in 84,032 archaeal and bacterial genomes, metagenome assembled genomes, and single-cell genomes. Homologs of MerA and MerB were identified in 7.8 and 2.1% percent of genomes, respectively. MerA was identified in the genomes of 10 archaeal and 28 bacterial phyla previously unknown to code for this functionality. Likewise, MerB was identified in 2 archaeal and 11 bacterial phyla previously unknown to encode this functionality. Surprisingly, homologs of MerB were identified in a number of genomes (∼50% of all MerB-encoding genomes) that did not encode MerA, suggesting alternative mechanisms to detoxify Hg(II) once it is generated in the cytoplasm. Phylogenetic reconstruction of MerA place its origin in thermophilic Thermoprotei (Crenarchaeota), consistent with high levels of Hg(II) in geothermal environments, the natural habitat of this archaeal class. MerB appears to have been recruited to the mer operon relatively recently and likely among a mesophilic ancestor of Euryarchaeota and Thaumarchaeota. This is consistent with the functional dependence of MerB on MerA and the widespread distribution of mesophilic microorganisms that methylate Hg(II) at lower temperature. Collectively, these results expand the taxonomic and ecological distribution of mer-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.
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- 2021
- Full Text
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12. 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
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Spencer Roth, Tamar Barkay, and Yelizaveta Rassadkina
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Hot spring ,Biogeochemical cycle ,biology ,Ecology ,Microorganism ,chemistry.chemical_element ,biology.organism_classification ,Mercury (element) ,Bioremediation ,chemistry ,Metagenomics ,General Earth and Planetary Sciences ,Environmental science ,Extreme environment ,General Environmental Science ,Archaea - Abstract
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.
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- 2020
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13. Tagging the vanA gene in wastewater microbial communities for cell sorting and taxonomy of vanA carrying cells
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Tamar Barkay, Sara Gallego, N.L. Fahrenfeld, Rutgers State Univ, Civil & Environm Engn, 500 Bartholomew Rd, Piscataway, NJ 08854 USA, Agroécologie [Dijon], Université de Bourgogne (UB)-AgroSup Dijon - Institut National Supérieur des Sciences Agronomiques, de l'Alimentation et de l'Environnement-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), and Rutgers State Univ, Dept Biochem & Microbiol, 76 Lipman Dr, New Brunswick, NJ 08901 USA
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Environmental Engineering ,antibiotic resistance ,010504 meteorology & atmospheric sciences ,[SDV]Life Sciences [q-bio] ,Microbial Sensitivity Tests ,010501 environmental sciences ,Wastewater ,01 natural sciences ,Microbiology ,Antibiotic resistance ,Microbial ecology ,Bacterial Proteins ,Environmental Chemistry ,Waste Management and Disposal ,Carbon-Oxygen Ligases ,In Situ Hybridization, Fluorescence ,Phylogeny ,0105 earth and related environmental sciences ,biology ,Microbiota ,two-pass TSA-FISH ,FACs ,Cell sorting ,biochemical phenomena, metabolism, and nutrition ,biology.organism_classification ,Pollution ,6. Clean water ,Anti-Bacterial Agents ,Microbial population biology ,Metagenomics ,Bacteria ,Enterococcus faecium - Abstract
National audience; Failure to understand the microbial ecology driving the proliferation of antibiotic resistance in the environment prevents us from developing strategies to limit the spread of antibiotic resistant infectious disease. In this study, we developed for the first time a tyramide signal amplification-fluorescence in situ hybridization-fluorescence-activated cell sorting protocol (TSA-FISH-FACS) for the characterization of all vanA carrying bacteria in wastewater samples. Firstly, we validated the TSA-FISH protocol through microscopy in pure cultures and wastewater influent. Then, samples were sorted and quantified by FACS and qPCR. Significantly higher percentage tagging of cells was detected in vanA carrying pure cultures and wastewater samples spiked with vanA carrying cells as compared to vanA negative Gram positive strains and non-spiked wastewater samples respectively. qPCR analysis targeting vanZ, a regulating gene in the vanA cluster, showed its relative abundance was significantly greater in Enterococcus faecium ATCC 700221-spiked and positively sorted samples compared to the E. faecium spiked and negatively sorted samples. Phylogenetic analysis was then performed. Although further efforts are needed to overcome technical problems, we have, for the first time, demonstrated sorting bacterial-cells carrying antibiotic resistance genes from wastewater samples through a TSA-FISH-FACS protocol and provided insight into the microbial ecology of vancomycin resistant bacteria. Future potential applications using this approach will include the separation of members of an environmental microbial community (cultured and hard-to-culture) to allow for metagenomics on single cells or, in the case of clumping, targeting a smaller portion of the community with a priori knowledge that the target gene is present.
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- 2020
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14. Binding of Hg by bacterial extracellular polysaccharide: a possible role in Hg tolerance
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Tamar Barkay, Jean Guezennec, and Kimberly Cruz
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0301 basic medicine ,030106 microbiology ,Mutant ,chemistry.chemical_element ,medicine.disease_cause ,Applied Microbiology and Biotechnology ,03 medical and health sciences ,medicine ,Biomass ,Microbial mat ,Escherichia coli ,Extracellular polysaccharide ,Bacteria ,Escherichia coli K12 ,biology ,Polysaccharides, Bacterial ,Sorption ,Exocellular polysaccharides ,Mercury ,General Medicine ,biology.organism_classification ,Mercury (element) ,030104 developmental biology ,Biochemistry ,chemistry ,Mutation ,Toxicity ,Adsorption ,Tolerance ,Biotechnology - Abstract
Bacteria employ adaptive mechanisms of mercury (Hg) tolerance to survive in environments containing elevated Hg concentrations. The potential of extracellular polysaccharides (EPS) production by bacteria as a mechanism of Hg tolerance has not been previously investigated. The objectives of this study were to determine if bacterial EPS sorb Hg, and if so does sorption provide protection against Hg toxicity. Purified EPS with different chemical compositions produced by bacterial isolates from microbial mats in French Polynesian atolls and deep-sea hydrothermal vents were assessed for Hg sorption. The data showed that EPS sorbed up to 82% of Hg from solution, that this sorption was dependent on EPS composition, and that sorption was a saturable mechanism. Hg uptake capacities ranged from 0.005 to 0.454 mmol Hg/g for the different EPS. To determine if EPS production could alter bacterial Hg tolerance, Escherichia coli K-12 strains and their EPS defective mutants were tested by the disc inhibition assay. Mercury inhibited growth in a dose-dependent manner with wild-type strains having smaller (~1 mm), but statistically significant, zones of inhibition than various mutants and this difference was related to a 2-fold decline in the amount of EPS produced by the mutants relative to cell biomass. These experiments identified colanic acid and hexosamine as Hg-binding moieties in EPS. Together these data indicate that binding of Hg to EPS affords a low level of resistance to the producing bacteria.
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- 2017
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15. Hg(II) reduction by siderite (FeCO3)
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Nathan Yee, Ri Qing Yu, Xiuhong Zhao, Juyoung Ha, and Tamar Barkay
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Electron transfer reactions ,X-ray absorption spectroscopy ,010504 meteorology & atmospheric sciences ,Inorganic chemistry ,chemistry.chemical_element ,010501 environmental sciences ,01 natural sciences ,Pollution ,Chemical reaction ,Anoxic waters ,Mercury (element) ,Reaction rate ,Siderite ,chemistry.chemical_compound ,Adsorption ,chemistry ,Geochemistry and Petrology ,Environmental chemistry ,Environmental Chemistry ,0105 earth and related environmental sciences - Abstract
In groundwater, chemical reactions of Hg(II) with mineral surfaces play an important role in determining the concentration of mercury that is mobile and bioavailable. In this study, we investigated Hg(II) reduction by the ferrous carbonate mineral, siderite (FeCO 3 ), to better understand reductive transformation of mercury in anoxic carbonate-bearing waters. Kinetic experiments and X-ray adsorption spectroscopy (XAS) were conducted to examine the rate and mechanism of Hg(II) reaction with siderite. Hg(II) was reacted with synthesized siderite mineral at various concentrations and the subsequently formed Hg(0) was measured to assess the extent of mercury reduction by siderite. Our experimental data showed that Hg(II) reduction by siderite resulted in the loss of Hg when reacted with siderite mineral suspensions concurrent to formation of gaseous Hg(0). Hg(II) reduction occurred within minutes and reaction rates increased with increasing siderite surface area. XAS analysis confirmed that Hg(II) was reduced to Hg(0) and revealed that reduced mercury was sorbed to siderite surfaces suggesting that electron transfer reactions occur at siderite/water interface. The results of our study suggest that Hg(II) reduction by siderite is a kinetically favorable pathway for the mercury mobilization in ferruginous carbonate-bearing waters.
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- 2017
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16. Effect of salinity on mercury methylating benthic microbes and their activities in Great Salt Lake, Utah
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Bonnie K. Baxter, Ri Qing Yu, Mark Marvin-DiPasquale, Tamar Barkay, Eric S. Boyd, David L. Naftz, and Trinity L. Hamilton
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0301 basic medicine ,Geologic Sediments ,Salinity ,Environmental Engineering ,030106 microbiology ,chemistry.chemical_element ,010501 environmental sciences ,Methylation ,01 natural sciences ,03 medical and health sciences ,chemistry.chemical_compound ,Benthos ,RNA, Ribosomal, 16S ,Utah ,Environmental Chemistry ,Sulfate ,Waste Management and Disposal ,Methylmercury ,0105 earth and related environmental sciences ,Bacteria ,Chemistry ,Ecology ,Biota ,Mercury ,Methylmercury Compounds ,Archaea ,Pollution ,Mercury (element) ,Lakes ,Benthic zone ,Environmental chemistry ,Water Microbiology ,Surface water ,Water Pollutants, Chemical ,Environmental Monitoring - Abstract
Surface water and biota from Great Salt Lake (GSL) contain some of the highest documented concentrations of total mercury (THg) and methylmercury (MeHg) in the United States. In order to identify potential biological sources of MeHg and controls on its production in this ecosystem, THg and MeHg concentrations, rates of Hg(II)-methylation and MeHg degradation, and abundances and compositions of archaeal and bacterial 16 rRNA gene transcripts were determined in sediment along a salinity gradient in GSL. Rates of Hg(II)-methylation were inversely correlated with salinity and were at or below the limits of detection in sediment sampled from areas with hypersaline surface water. The highest rates of Hg(II)-methylation were measured in sediment with low porewater salinity, suggesting that benthic microbial communities inhabiting less saline environments are supplying the majority of MeHg in the GSL ecosystem. The abundance of 16S rRNA gene transcripts affiliated with the sulfate reducer Desulfobacterium sp. was positively correlated with MeHg concentrations and Hg(II)-methylation rates in sediment, indicating a potential role for this taxon in Hg(II)-methylation in low salinity areas of GSL. Reactive inorganic Hg(II) (a proxy used for Hg(II) available for methylation) and MeHg concentrations were inversely correlated with salinity. Thus, constraints imposed by salinity on Hg(II)-methylating populations and the availability of Hg(II) for methylation are inferred to result in higher MeHg production potentials in lower salinity environments. Benthic microbial MeHg degradation was also most active in lower salinity environments. Collectively, these results suggest an important role for sediment anoxia and microbial sulfate reducers in the production of MeHg in low salinity GSL sub-habitats and may indicate a role for salinity in constraining Hg(II)-methylation and MeHg degradation activities by influencing the availability of Hg(II) for methylation.
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- 2017
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17. Expression and regulation of the mer operon in Thermus thermophilus
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Tamar Barkay, Maximilian Miller, Javiera Norambuena, and Jeffrey M. Boyd
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Operon ,Hypothetical protein ,Repressor ,Microbiology ,03 medical and health sciences ,Bacterial Proteins ,Transcription (biology) ,Transcriptional regulation ,Promoter Regions, Genetic ,Ecology, Evolution, Behavior and Systematics ,030304 developmental biology ,0303 health sciences ,biology ,030306 microbiology ,Thermophile ,Thermus thermophilus ,food and beverages ,Promoter ,Mercury ,biology.organism_classification ,Molecular biology ,DNA-Binding Proteins ,bacteria ,Oxidoreductases ,Transcription Factors - Abstract
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.
- Published
- 2019
18. Toxicity Testing in Soil Using Microorganisms
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Betty H. Olson, Tamar Barkay, and O. F. Shearer
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Microorganism ,Environmental chemistry ,Toxicity ,Environmental science - Published
- 2019
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19. Genome-facilitated discovery of RND efflux pump-mediated resistance to cephalosporins in Vibrio spp. isolated from the mummichog fish gut
- Author
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Nicole A. Lloyd, Sylvie Nazaret, Tamar Barkay, Laboratoire d'Ecologie Microbienne - UMR 5557 (LEM), Institut National de la Recherche Agronomique (INRA)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Ecole Nationale Vétérinaire de Lyon (ENVL)-VetAgro Sup - Institut national d'enseignement supérieur et de recherche en alimentation, santé animale, sciences agronomiques et de l'environnement (VAS)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Ecole Nationale Vétérinaire de Lyon (ENVL)-Université Claude Bernard Lyon 1 (UCBL), and Université de Lyon-Université de Lyon-Institut National de la Recherche Agronomique (INRA)-VetAgro Sup - Institut national d'enseignement supérieur et de recherche en alimentation, santé animale, sciences agronomiques et de l'environnement (VAS)
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0301 basic medicine ,Microbiology (medical) ,Operon ,[SDV]Life Sciences [q-bio] ,030106 microbiology ,Immunology ,Cefsulodin ,Virulence ,Microbial Sensitivity Tests ,Biology ,medicine.disease_cause ,Microbiology ,03 medical and health sciences ,0302 clinical medicine ,Resistance-nodulation-cell division (RND) ,Bacterial Proteins ,Fundulidae ,Drug Resistance, Bacterial ,medicine ,Animals ,Immunology and Allergy ,Efflux pumps ,030212 general & internal medicine ,Escherichia coli ,ComputingMilieux_MISCELLANEOUS ,Vibrio ,[SDV.EE]Life Sciences [q-bio]/Ecology, environment ,Membrane Transport Proteins ,Kanamycin ,biology.organism_classification ,Cephalosporin resistance ,Anti-Bacterial Agents ,Cephalosporins ,Gastrointestinal Tract ,Vibrio cholerae ,[SDE]Environmental Sciences ,Food Microbiology ,Efflux ,[SDE.BE]Environmental Sciences/Biodiversity and Ecology ,Genome, Bacterial ,Bacterial Outer Membrane Proteins ,medicine.drug - Abstract
International audience; Objectives: This study examined the role of resistance-nodulation-cell division (RND) efflux pumps in resistance to first-generation and third-generation cephalosporins, and the potential contribution to increased virulence in two Vibrio isolates from the gut microbiota of a forage-feeder fish. Methods: Phenotypic MIC testing was performed in the presence and absence of an RND efflux pump inhibitor, phenylalanine-arginine-beta-napthylamide (PA beta N). Genomes of the two Vibrio spp. were compared to characterise RND efflux pump gene homologs. Results: The study identified 13 and 12 RND operons, respectively, in Vibrio spp. T21 and T9, with Vibrio sp. T21 containing an additional RND operon compared with other V. parahaemolyticus strains. Both the inner-membrane protein (IMP) and the membrane facilitator protein (MFP) sequences of this operon were homologous to VexD and VexC, respectively, which is an RND operon in Vibrio cholerae. More generally, the other RND proteins in these strains showed homology to RND efflux pumps characterised in Escherichia coli and Vibrio cholerae. Decreased resistance to cefoperazone and cephradine was observed in Vibrio sp. T21, and to cefoperazone and cefsulodin in Vibrio sp. T9 in the presence of Pa beta N. The RND pumps may also mediate transport of kanamycin. Conclusions: By analysing the genomes of two Vibrio spp. isolated from the mummichog fish gut, RND efflux pump-mediated resistance to first-generation and third-generation cephalosporins was discovered in these strains. This work highlights the need for further research into this unique Vibrio spp. operon and, more generally, RND efflux pumps in Vibrio spp., as Vibrio spp. often cause seafood-borne illness. (C) 2019 International Society for Antimicrobial Chemotherapy. Published by Elsevier Ltd. All rights reserved.
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- 2019
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20. Co-selection of Mercury and Multiple Antibiotic Resistances in Bacteria Exposed to Mercury in the Fundulus heteroclitus Gut Microbiome
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Nicole A. Lloyd, John R. Reinfelder, Tamar Barkay, and Sarah E. Janssen
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0301 basic medicine ,Antibiotic resistance ,medicine.drug_class ,Mercury resistance ,Antibiotics ,chemistry.chemical_element ,Drug resistance ,010501 environmental sciences ,medicine.disease_cause ,01 natural sciences ,Applied Microbiology and Biotechnology ,Microbiology ,03 medical and health sciences ,Bacterial Proteins ,Fundulidae ,Drug Resistance, Bacterial ,medicine ,Animals ,Humans ,Mummichog (Fundulus heteroclitus) ,0105 earth and related environmental sciences ,Bacteria ,biology ,Ecology ,Pathogenic bacteria ,Mercury ,General Medicine ,Co-resistance ,biology.organism_classification ,Anti-Bacterial Agents ,Gastrointestinal Microbiome ,Mercury (element) ,Fundulus ,Gastrointestinal Tract ,Mummichog ,030104 developmental biology ,chemistry - Abstract
The emergence and spread of antibiotic-resistant pathogenic bacteria is currently one of the most serious challenges to human health. To combat this problem, it is critical to understand the processes and pathways that result in the creation of antibiotic resistance gene pools in the environment. In this study, we examined the effects of mercury (Hg) exposure on the co-selection of Hg and antibiotic-resistant bacteria that colonize the gastrointestinal tract of the mummichog (Fundulus heteroclitus), a small, estuarine fish. We examined this connection in two experimental systems: (i) a short-term laboratory exposure study where fish were fed Hg-laced food for 15 days and (ii) an examination of environmental populations from two sites with very different levels of Hg contamination. In the lab exposure study, fish muscle tissue accumulation of Hg was proportional to food Hg concentration (R 2 = 0.99; P
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- 2016
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21. Fractionation of Mercury Stable Isotopes during Microbial Methylmercury Production by Iron- and Sulfate-Reducing Bacteria
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John R. Reinfelder, Tamar Barkay, Jeffra K. Schaefer, and Sarah E. Janssen
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010504 meteorology & atmospheric sciences ,Iron ,chemistry.chemical_element ,Fractionation ,010501 environmental sciences ,Methylation ,01 natural sciences ,chemistry.chemical_compound ,Environmental Chemistry ,Sulfate-reducing bacteria ,Geobacter sulfurreducens ,Methylmercury ,0105 earth and related environmental sciences ,biology ,Sulfates ,Stable isotope ratio ,Mercury ,General Chemistry ,Methylmercury Compounds ,biology.organism_classification ,Mercury (element) ,Mercury Isotopes ,chemistry ,Environmental chemistry ,Anaerobic bacteria ,Water Pollutants, Chemical ,Bacteria - Abstract
The biological production of monomethylmercury (MeHg) in soils and sediments is an important factor controlling mercury (Hg) accumulation in aquatic and terrestrial food webs. In this study we examined the fractionation of Hg stable isotopes during Hg methylation in nongrowing cultures of the anaerobic bacteria Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. Both organisms showed mass-dependent, but no mass-independent fractionation of Hg stable isotopes during Hg methylation. Despite differences in methylation rates, the two bacteria had similar Hg fractionation factors (αr/p = 1.0009 and 1.0011, respectively). Unexpectedly, δ(202)Hg values of MeHg for both organisms were 0.4‰ higher than the value of initial inorganic Hg after about 35% of inorganic Hg had been methylated. These results indicate that a (202)Hg-enriched pool of inorganic Hg was preferentially utilized as a substrate for methylation by these organisms, but that multiple intra- and/or extracellular pools supplied inorganic Hg for biological methylation. Understanding the controls of the Hg stable isotopic composition of microbially produced MeHg is important to identifying bioavailable Hg in natural systems and the interpretation of Hg stable isotopes in aquatic food webs.
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- 2016
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22. Anaerobic Mercury Methylation and Demethylation by Geobacter bemidjiensis Bem
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Alexander Johs, Liyuan Liang, Tamar Barkay, Xia Lu, Hui Lin, Dwayne A. Elias, Baohua Gu, Eric M. Pierce, Tieshan Wang, Yu-Rong Liu, Ziming Yang, and Linduo Zhao
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0301 basic medicine ,Iron ,030106 microbiology ,Lyases ,010501 environmental sciences ,Methylation ,01 natural sciences ,03 medical and health sciences ,chemistry.chemical_compound ,Environmental Chemistry ,Anaerobiosis ,Cysteine ,Methylmercury ,0105 earth and related environmental sciences ,Demethylation ,Geobacter bemidjiensis ,biology ,Mercury ,General Chemistry ,Methylmercury Compounds ,biology.organism_classification ,Anoxic waters ,Biodegradation, Environmental ,chemistry ,Environmental chemistry ,Bioaccumulation ,Environmental Pollutants ,Anaerobic bacteria ,Geobacter ,Oxidoreductases ,Oxidation-Reduction ,Bacteria - Abstract
Microbial methylation and demethylation are two competing processes controlling the net production and bioaccumulation of neurotoxic methylmercury (MeHg) in natural ecosystems. Although mercury (Hg) methylation by anaerobic microorganisms and demethylation by aerobic Hg-resistant bacteria have both been extensively studied, little attention has been given to MeHg degradation by anaerobic bacteria, particularly the iron-reducing bacterium Geobacter bemidjiensis Bem. Here we report, for the first time, that the strain G. bemidjiensis Bem can mediate a suite of Hg transformations, including Hg(II) reduction, Hg(0) oxidation, MeHg production and degradation under anoxic conditions. Results suggest that G. bemidjiensis utilizes a reductive demethylation pathway to degrade MeHg, with elemental Hg(0) as the major reaction product, possibly due to the presence of genes encoding homologues of an organomercurial lyase (MerB) and a mercuric reductase (MerA). In addition, the cells can strongly sorb Hg(II) and MeHg, reduce or oxidize Hg, resulting in both time and concentration-dependent Hg species transformations. Moderate concentrations (10-500 μM) of Hg-binding ligands such as cysteine enhance Hg(II) methylation but inhibit MeHg degradation. These findings indicate a cycle of Hg methylation and demethylation among anaerobic bacteria, thereby influencing net MeHg production in anoxic water and sediments.
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- 2016
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23. Whole genome sequences to assess the link between antibiotic and metal resistance in three coastal marine bacteria isolated from the mummichog gastrointestinal tract
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Nicole A. Lloyd, Sylvie Nazaret, Tamar Barkay, Laboratoire d'Ecologie Microbienne - UMR 5557 (LEM), Centre National de la Recherche Scientifique (CNRS)-Ecole Nationale Vétérinaire de Lyon (ENVL)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut National de la Recherche Agronomique (INRA)-VetAgro Sup - Institut national d'enseignement supérieur et de recherche en alimentation, santé animale, sciences agronomiques et de l'environnement (VAS), Institut National de la Recherche Agronomique (INRA)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Ecole Nationale Vétérinaire de Lyon (ENVL)-VetAgro Sup - Institut national d'enseignement supérieur et de recherche en alimentation, santé animale, sciences agronomiques et de l'environnement (VAS)-Centre National de la Recherche Scientifique (CNRS), New Jersey Water Resources Research Institute USGS-G16AP00071(07043), and Chateaubriand Fellowship of the Office for Science & Technology of the Embassy of France in the United States
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0301 basic medicine ,[SDV]Life Sciences [q-bio] ,030106 microbiology ,Drug resistance ,Aquatic Science ,Gut flora ,Oceanography ,Genome ,03 medical and health sciences ,Antibiotic resistance ,Fundulidae ,Animals ,Gene ,Genetics ,[SDV.EE]Life Sciences [q-bio]/Ecology, environment ,biology ,Bacteria ,Whole Genome Sequencing ,Drug Resistance, Microbial ,biology.organism_classification ,Pollution ,Vibrio ,3. Good health ,Mummichog ,Gastrointestinal Tract ,030104 developmental biology ,Genes, Bacterial ,Metals ,[SDE]Environmental Sciences ,Efflux ,[SDE.BE]Environmental Sciences/Biodiversity and Ecology ,Water Microbiology - Abstract
International audience; Antibiotic resistance is a global public health issue and metal exposure can co-select for antibiotic resistance. We examined genome sequences of three multi-drug and metal resistant bacteria: one Shewanella sp., and two Vibrio spp., isolated from the gut of the mummichog fish (Fundulus heteroclitus). Our primary goal was to understand the mechanisms of co-selection. Phenotypically, the strains showed elevated resistance to arsenate, mercury, and various types of β-lactams. The genomes contained genes of public health concern including one carbapenemase (bla OXA-48). Our analyses indicate that the co-selection phenotype is mediated by chromo-somal resistance genes and cross-resistance. No evidence of co-resistance was found; most resistance genes were chromosomally located. Moreover, the identification of many efflux pump gene homologs indicates that cross-resistance and/or co-regulation may further contribute to resistance. We suggest that the mummichog gut microbiota may be a source of clinically relevant antibiotic resistance genes.
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- 2018
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24. Syntrophic pathways for microbial mercury methylation
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Ri Qing Yu, Mark E. Hines, John R. Reinfelder, and Tamar Barkay
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0301 basic medicine ,Deltaproteobacteria ,Iron ,030106 microbiology ,chemistry.chemical_element ,010501 environmental sciences ,Biology ,01 natural sciences ,Microbiology ,Methylation ,Article ,03 medical and health sciences ,chemistry.chemical_compound ,Syntrophy ,Sulfate ,Methylmercury ,Ecology, Evolution, Behavior and Systematics ,0105 earth and related environmental sciences ,Sulfates ,Mercury ,Methylmercury Compounds ,biology.organism_classification ,Anoxic waters ,Methanogen ,Mercury (element) ,chemistry ,Environmental chemistry ,Oxidation-Reduction ,Bacteria - Abstract
Exposure to dietary sources of methylmercury (MeHg) is the focus of public health concerns with environmental mercury (Hg) contamination. MeHg is formed in anoxic environments by anaerobic microorganisms. This process has been studied mostly with single-species culture incubations, although the relevance of such studies to Hg(II)-methylation in situ is limited because microbial activities in the environment are critically modulated by interactions among microbial functional groups. Here we describe experiments in which Hg(II)-methylation was examined within the context of various microbial syntrophies. We show enhanced Hg(II)-methylation under conditions that established syntrophy by interspecies hydrogen and acetate transfer. Relative to activity of monocultures, interactions of Hg(II) methylating sulfate-reducing bacteria with a methanogen stimulated potential Hg(II)-methylation rates 2-fold to 9-fold, and with Syntrophobacter sp. 1.7-fold to 1.8-fold; those of a Hg(II) methylating Syntrophobacter sp. with a methanogen increased Hg(II)-methylation 2-fold. Under sulfate-depleted conditions, higher Hg(II)-methylation rates in the syntrophic incubations corresponded to higher free energy yields (ΔG°') than in the monocultures. Based on energetic considerations, we therefore propose that syntrophic microbial interactions are likely a major source of MeHg in sulfate- and iron-limited anoxic environments while in sulfate-replete environments, MeHg formation via sulfate reduction dominates.
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- 2018
25. Low-Molecular-Weight Thiols and Thioredoxins Are Important Players in Hg(II) Resistance in Thermus thermophilus HB27
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Javiera Norambuena, Tamar Barkay, Jeffrey M. Boyd, Thomas E. Hanson, and Yanping Wang
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0301 basic medicine ,Operon ,Physiology ,030106 microbiology ,Drug Resistance ,Metal toxicity ,Applied Microbiology and Biotechnology ,03 medical and health sciences ,chemistry.chemical_compound ,Thioredoxins ,Bacterial Proteins ,Sulfhydryl Compounds ,chemistry.chemical_classification ,Ecology ,biology ,Thermus ,Thermus thermophilus ,Mercury ,biology.organism_classification ,Molecular Weight ,030104 developmental biology ,Biochemistry ,chemistry ,Bacillithiol ,Thiol ,Environmental Pollutants ,Thioredoxin ,Food Science ,Biotechnology ,Cysteine - Abstract
Mercury (Hg), one of the most toxic and widely distributed heavy metals, has a high affinity for thiol groups. Thiol groups reduce and sequester Hg. Therefore, low-molecular-weight (LMW) and protein thiols may be important cell components used in Hg resistance. To date, the role of low-molecular-weight thiols in Hg detoxification remains understudied. The mercury resistance ( mer ) operon of Thermus thermophilus suggests an evolutionary link between Hg(II) resistance and low-molecular-weight thiol metabolism. The mer operon encodes an enzyme involved in methionine biosynthesis, Oah. Challenge with Hg(II) resulted in increased expression of genes involved in the biosynthesis of multiple low-molecular-weight thiols (cysteine, homocysteine, and bacillithiol), as well as the thioredoxin system. Phenotypic analysis of gene replacement mutants indicated that Oah contributes to Hg resistance under sulfur-limiting conditions, and strains lacking bacillithiol and/or thioredoxins are more sensitive to Hg(II) than the wild type. Growth in the presence of either a thiol-oxidizing agent or a thiol-alkylating agent increased sensitivity to Hg(II). Furthermore, exposure to 3 μM Hg(II) consumed all intracellular reduced bacillithiol and cysteine. Database searches indicate that oah2 is present in all Thermus sp. mer operons. The presence of a thiol-related gene was also detected in some alphaproteobacterial mer operons, in which a glutathione reductase gene was present, supporting the role of thiols in Hg(II) detoxification. These results have led to a working model in which LMW thiols act as Hg(II)-buffering agents while Hg is reduced by MerA. IMPORTANCE The survival of microorganisms in the presence of toxic metals is central to life's sustainability. The affinity of thiol groups for toxic heavy metals drives microbe-metal interactions and modulates metal toxicity. Mercury detoxification ( mer ) genes likely originated early in microbial evolution in geothermal environments. Little is known about how mer systems interact with cellular thiol systems. Thermus spp. possess a simple mer operon in which a low-molecular-weight thiol biosynthesis gene is present, along with merR and merA . In this study, we present experimental evidence for the role of thiol systems in mercury resistance. Our data suggest that, in T. thermophilus , thiolated compounds may function side by side with mer genes to detoxify mercury. Thus, thiol systems function in consort with mer -mediated resistance to mercury, suggesting exciting new questions for future research.
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- 2018
26. The effect of aqueous speciation and cellular ligand binding on the biotransformation and bioavailability of methylmercury in mercury-resistant bacteria
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Udonna Ndu, Robert P. Mason, Amina T. Schartup, John R. Reinfelder, and Tamar Barkay
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0301 basic medicine ,Environmental Engineering ,Microorganism ,030106 microbiology ,chemistry.chemical_element ,Bioengineering ,Biosensing Techniques ,010501 environmental sciences ,Ligands ,01 natural sciences ,Microbiology ,03 medical and health sciences ,chemistry.chemical_compound ,Biotransformation ,Escherichia coli ,Environmental Chemistry ,Cysteine ,Sulfhydryl Compounds ,Methylmercury ,0105 earth and related environmental sciences ,Demethylation ,Pseudomonas stutzeri ,Bacteria ,biology ,Chemistry ,Membranes, Artificial ,Mercury ,Methylmercury Compounds ,biology.organism_classification ,Glutathione ,Pollution ,Mercury (element) ,Bioavailability ,Biodegradation, Environmental ,Environmental chemistry ,Environmental Pollutants - Abstract
Mercury resistant bacteria play a critical role in mercury biogeochemical cycling in that they convert methylmercury (MeHg) and inorganic mercury to elemental mercury, Hg(0). To date there are very few studies on the effects of speciation and bioavailability of MeHg in these organisms, and even fewer studies on the role that binding to cellular ligands plays on MeHg uptake. The objective of this study was to investigate the effects of thiol complexation on the uptake of MeHg by measuring the intracellular demethylation-reduction (transformation) of MeHg to Hg(0) in Hg-resistant bacteria. Short-term intracellular transformation of MeHg was quantified by monitoring the loss of volatile Hg(0) generated during incubations of bacteria containing the complete mer operon (including genes from putative mercury transporters) exposed to MeHg in minimal media compared to negative controls with non-mer or heat-killed cells. The results indicate that the complexes MeHgOH, MeHg-cysteine, and MeHg-glutathione are all bioavailable in these bacteria, and without the mer operon there is very little biological degradation of MeHg. In both Pseudomonas stutzeri and Escherichia coli, there was a pool of MeHg that was not transformed to elemental Hg(0), which was likely rendered unavailable to Mer enzymes by non-specific binding to cellular ligands. Since the rates of MeHg accumulation and transformation varied more between the two species of bacteria examined than among MeHg complexes, microbial bioavailability, and therefore microbial demethylation, of MeHg in aquatic systems likely depends more on the species of microorganism than on the types and relative concentrations of thiols or other MeHg ligands present.
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- 2015
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27. Separation of monomethylmercury from estuarine sediments for mercury isotope analysis
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John R. Reinfelder, Joel D. Blum, Sarah E. Janssen, Marcus W. Johnson, and Tamar Barkay
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Chemistry ,Stable isotope ratio ,Sediment ,chemistry.chemical_element ,Geology ,Fractionation ,Mercury (element) ,Isotopic signature ,chemistry.chemical_compound ,Geochemistry and Petrology ,Environmental chemistry ,Methylmercury ,Inductively coupled plasma mass spectrometry ,Isotope analysis - Abstract
Estuarine sediments support the production of monomethylmercury (MeHg) which accumulates in aquatic organisms. While natural variation in mercury stable isotope ratios can potentially be used to track sources and transformations of mercury in the environment, the isotopic signature of MeHg in sediments has not been measured directly. The isotopic composition of MeHg has been studied in laboratory experiments and fish using tandem gas chromatography-multicollector inductively coupled plasma mass spectrometry (MC–ICP-MS) systems; however, the precision and sensitivity of this method may be too low for the analysis of many environmental samples including sediments in which MeHg constitutes 1% or less of the total mercury. In this study, we developed an offline separation method for the precise measurement of the Hg isotopic composition of MeHg in estuarine sediments. Separation of MeHg from inorganic species was accomplished by distillation and chemical ethylation-GC, and was followed by gold amalgam trapping to collect and preconcentrate pyrolyzed MeHg, which was then released into an oxidizing solution. MeHg standards processed in this way were collected with an average yield of 97.5%. External precision for all replicate isotope analyses of MeHg process standards was ± 0.14‰ (2 SD, n = 8) for δ202Hg and no detectable fractionation of Hg stable isotopes occurred during the separation. δ202Hg values for MeHg separated from estuarine sediments using our approach varied from − 0.41 to + 0.41‰ and were generally higher, and spatially and temporally more variable, than those for total Hg (− 0.21 to − 0.48‰).
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- 2015
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28. Mercury and methylmercury detoxification potential by sponge-associated bacteria
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Marcia Giambiagi-deMarval, Tamar Barkay, Guilherme Muricy, Juliana F. Santos-Gandelman, and Marinella S. Laport
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Microbial metabolism ,chemistry.chemical_element ,Microbiology ,chemistry.chemical_compound ,Bioremediation ,Biotransformation ,Drug Resistance, Bacterial ,Animals ,Molecular Biology ,Methylmercury ,Colony-forming unit ,Bacteria ,biology ,General Medicine ,Methylmercury Compounds ,biology.organism_classification ,Porifera ,Mercury (element) ,Sponge ,chemistry ,Environmental chemistry ,Mercuric Chloride ,Environmental Pollutants ,Brazil - Abstract
Ionic and organic forms of mercury (Hg) are powerful cytotoxic and neurotoxic agents in both humans and wild life. The aim of this study was to analyze the resistance profile and potential detoxification of inorganic and organic forms of Hg of bacteria isolated from marine sponges on the coast of Rio de Janeiro, Brazil. Out of the 1,236 colony forming units associated with eleven species of marine sponges, 100 morphologically different bacterial strains were analyzed in this study. Of these, 21 strains were resistant to Hg, 14 of which were classified as highly resistant because they grew despite exposure to 100 µM HgCl2. Fifteen resistant strains reduced Hg and presented merA in their genomes. The remaining six strains produced biosurfactants, suggesting that they may tolerate Hg by sequestration. Eleven strains grew in the presence of methylmercury. Our results suggest a potential for mercury detoxification by marine sponge-associated resistant bacteria, either through reduction or sequestration, as well as the possibility of bioremediation of toxic waste containing mercury.
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- 2014
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29. Potential Application in Mercury Bioremediation of a Marine Sponge-Isolated Bacillus cereus strain Pj1
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Tamar Barkay, Juliana F. Santos-Gandelman, Sharron Crane, Guilherme Muricy, Marinella S. Laport, Kimberly Cruz, and Marcia Giambiagi-deMarval
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Microorganism ,Bacillus cereus ,chemistry.chemical_element ,Applied Microbiology and Biotechnology ,Microbiology ,Breast Diseases ,Bioremediation ,Cadmium Chloride ,Drug Resistance, Bacterial ,Operon ,Animals ,Nitrates ,biology ,General Medicine ,Marine invertebrates ,Chromosomes, Bacterial ,Methylmercury Compounds ,Biodegradation ,biology.organism_classification ,Mercury (element) ,Sponge ,Biodegradation, Environmental ,Lead ,chemistry ,Cereus ,Nipples ,Environmental chemistry ,Mercuric Chloride ,Environmental Pollutants - Abstract
Sponges are sessile marine invertebrates that can live for many years in the same location, and therefore, they have the capability to accumulate anthropogenic pollutants such as metals over a long period. Almost all marine sponges harbor a large number of microorganisms within their tissues. The Bacillus cereus strain Pj1 was isolated from a marine sponge, Polymastia janeirensis, and was found to be resistant to 100 μM HgCl(2) and to 10 μM methylmercury (MeHg). Pj1 was also highly resistant to other metals, including CdCl(2) and Pb(NO(3))(2), alone or in combination. The mer operon was located on the bacterial chromosome, and the volatilization test indicated that the B. cereus Pj1 was able to reduce Hg(2+)-Hg(0). Cold vapor atomic absorption spectrometry demonstrated that Pj1 volatilized 80 % of the total MeHg that it was exposed to and produced elemental Hg when incubated with 1.5 μM MeHg. Pj1 also demonstrated sensitivity to all antibiotics tested. In addition, Pj1 demonstrated a potential for biosurfactant production, presenting an emulsification activity better than synthetic surfactants. The results of this study indicate that B. cereus Pj1 is a strain that can potentially be applied in the bioremediation of HgCl(2) and MeHg contamination in aquatic environments.
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- 2014
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30. Oxidation of Hg(0) to Hg(II) by diverse anaerobic bacteria
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Matthew J. Colombo, Juyoung Ha, John R. Reinfelder, Tamar Barkay, and Nathan Yee
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biology ,Chemistry ,Cupriavidus metallidurans ,chemistry.chemical_element ,Geology ,Geothrix fermentans ,medicine.disease_cause ,biology.organism_classification ,Redox ,Anoxic waters ,Mercury (element) ,Geochemistry and Petrology ,Environmental chemistry ,medicine ,Anaerobic bacteria ,Shewanella oneidensis ,Bacteria - Abstract
Redox cycling between elemental [Hg(0)] and divalent [Hg(II)] mercury is a key control on the fate and transport of Hg in groundwater systems. In this study, we tested the ability of anaerobic bacteria to oxidize dissolved Hg(0) to Hg(II). Controlled laboratory experiments were carried out with the obligate anaerobic bacterium Geothrix fermentans H5, and the facultative anaerobic bacteria Shewanella oneidensis MR-1 and Cupriavidus metallidurans AE104. Under anoxic conditions, all three bacterial strains reacted with dissolved gaseous Hg(0) to form non-purgeable Hg. In mass balance experiments, the formation of non-purgeable Hg corresponded to the loss of volatile Hg. To determine if the non-purgeable Hg was oxidized, we performed ethylation experiments on Hg(0)-reacted cell suspensions and X-ray absorption near edge structure (XANES) spectroscopy on Hg(0)-reacted cells. Derivatization of non-purgeable Hg to diethylmercury and the Hg L III -edge position of the XANES spectra demonstrated that the reacted bacterial samples contained Hg(II). XANES analysis also revealed that cell-associated Hg(II) was covalently bound to bacterial functional groups, most likely to thiol moieties. Finally, experiments with metabolically active and heat-inactivated cells indicated that both live and dead cells oxidized Hg(0) to Hg(II). Hg(0) oxidation rates for metabolically active cultures increase in the order S. oneidensis MR-1 (1.6 × 10 − 4 fg/cell/min), C. metallidurans AE104 (2.5 × 10 − 4 fg/cell/min), and G. fermentans H5 (23.1 × 10 − 4 fg/cell/min). The results of this study suggest that reactivity towards Hg(0) is widespread among diverse anaerobic bacteria, and passive microbial oxidation of Hg(0) may play an important role in the redox transformation of mercury contaminants in subsurface environments.
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- 2014
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31. In Memoriam of Mark Hines, 1950–2018
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Jadran Faganeli and Tamar Barkay
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Earth and Planetary Sciences (miscellaneous) ,Environmental Chemistry ,Microbiology ,General Environmental Science - Published
- 2018
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32. Syntrophic Effects in a Subsurface Clostridial Consortium on Fe(III)-(Oxyhydr)oxide Reduction and Secondary Mineralization
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Nathan Yee, Xiuhong Zhao, Yangping Wang, Chu-Ching Lin, Tamar Barkay, Ravi K. Kukkadapu, Mark H. Engelhard, and Madhavi Shah
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chemistry.chemical_classification ,Strain (chemistry) ,Sulfide ,biology ,Iron oxide ,biology.organism_classification ,Microbiology ,Mineralization (biology) ,Clostridia ,chemistry.chemical_compound ,chemistry ,Earth and Planetary Sciences (miscellaneous) ,Environmental Chemistry ,Fermentation ,Food science ,Dissolution ,Bacteria ,General Environmental Science - Abstract
In this study, we cultivated from subsurface sediments an anaerobic clostridial consortium that was composed of a fermentative Fe-reducer Clostridium species (designated as strain FGH) and a novel sulfate-reducing bacterium belonging to the clostridia family Vellionellaceae (designated as strain RU4). In pure culture, Clostridium sp. strain FGH mediated the reductive dissolution/transformation of iron oxides during growth on peptone. When Clostridium sp. FGH was grown with strain RU4 on peptone, the rates of iron oxide reduction were significantly higher. Iron reduction by the consortium was mediated by multiple mechanisms, including biotic reduction by Clostridium sp. FGH and biotic/abiotic reactions involving biogenic sulfide formed by strain RU4. The Clostridium sp. FGH produced hydrogen during fermentation, and the presence of hydrogen inhibited growth and iron reduction activity. The sulfate-reducing partner strain RU4 was stimulated by the presence of H2and generated reactive sulfide which promoted ...
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- 2013
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33. Mercury Methylation by the Methanogen Methanospirillum hungatei
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John R. Reinfelder, Ri Qing Yu, Mark E. Hines, and Tamar Barkay
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animal structures ,Archaeal Proteins ,chemistry.chemical_element ,Sulfides ,Methylation ,Applied Microbiology and Biotechnology ,Methanospirillum ,chemistry.chemical_compound ,Environmental Microbiology ,Cluster Analysis ,Sulfate ,Methylmercury ,Phylogeny ,Ecology ,biology ,Mercury ,Sequence Analysis, DNA ,Methylmercury Compounds ,biology.organism_classification ,Methanogen ,Anoxic waters ,Culture Media ,Mercury (element) ,chemistry ,Biochemistry ,Methanospirillum hungatei ,Bacteria ,Food Science ,Biotechnology - Abstract
Methylmercury (MeHg), a neurotoxic substance that accumulates in aquatic food chains and poses a risk to human health, is synthesized by anaerobic microorganisms in the environment. To date, mercury (Hg) methylation has been attributed to sulfate- and iron-reducing bacteria (SRB and IRB, respectively). Here we report that a methanogen, Methanospirillum hungatei JF-1, methylated Hg in a sulfide-free medium at comparable rates, but with higher yields, than those observed for some SRB and IRB. Phylogenetic analyses showed that the concatenated orthologs of the Hg methylation proteins HgcA and HgcB from M. hungatei are closely related to those from known SRB and IRB methylators and that they cluster together with proteins from eight other methanogens, suggesting that these methanogens may also methylate Hg. Because all nine methanogens with HgcA and HgcB orthologs belong to the class Methanomicrobia , constituting the late-evolving methanogenic lineage, methanogenic Hg methylation could not be considered an ancient metabolic trait. Our results identify methanogens as a new guild of Hg-methylating microbes with a potentially important role in mineral-poor (sulfate- and iron-limited) anoxic freshwater environments.
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- 2013
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34. Anaerobic oxidation of Hg(0) and methylmercury formation by Desulfovibrio desulfuricans ND132
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Juyoung Ha, Matthew J. Colombo, Nathan Yee, John R. Reinfelder, and Tamar Barkay
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chemistry.chemical_classification ,chemistry.chemical_compound ,Diethylmercury ,chemistry ,Geochemistry and Petrology ,Environmental chemistry ,Thiol ,Anaerobic bacteria ,Derivatization ,Incubation ,Anoxic waters ,Mercury cycle ,Methylmercury - Abstract
The transformation of inorganic mercury (Hg) to methylmercury (MeHg) plays a key role in determining the amount of Hg that is bioaccumulated in aquatic food chains. An accurate knowledge of Hg methylation mechanisms is required to predict the conditions that promote MeHg production in aquatic environments. In this study, we conducted experiments to examine the oxidation and methylation of dissolved elemental mercury [Hg(0)] by the anaerobic bacterium Desulfovibrio desulfuricans ND132. Anoxic cultures of D. desulfuricans ND132 were exposed to Hg(0) in the dark, and samples were collected and analyzed for the loss of Hg(0), formation of non-purgeable Hg, and formation of MeHg over time. We found that D. desulfuricans ND132 rapidly transformed dissolved gaseous mercury into non-purgeable Hg, with bacterial cultures producing approximately 40 μg/L of non-purgeable Hg within 30 min, and as much as 800 μg/L of non-purgeable Hg after 36 h. Derivatization of the non-purgeable Hg in the cell suspensions to diethylmercury and analysis of Hg(0)-reacted D. desulfuricans ND132 cells using X-ray absorption near edge structure (XANES) spectroscopy demonstrated that cell-associated Hg was dominantly in the oxidized Hg(II) form. Spectral comparisons and linear combination fitting of the XANES spectra indicated that the oxidized Hg(II) was covalently bonded to cellular thiol functional groups. MeHg analyses revealed that D. desulfuricans ND132 produced up to 118 μg/L of methylmercury after 36 h of incubation. We found that a significant fraction of the methylated Hg was exported out of the cell and released into the culture medium. The results of this work demonstrate a previously unrecognized pathway in the mercury cycle, whereby anaerobic bacteria produce MeHg when provided with dissolved Hg(0) as their sole Hg source.
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- 2013
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35. Microbial stable isotope fractionation of mercury: A synthesis of present understanding and future directions
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Joel D. Blum, K. Kritee, John R. Reinfelder, and Tamar Barkay
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Isotope fractionation ,Volatilisation ,chemistry ,Isotope ,Geochemistry and Petrology ,Stable isotope ratio ,Environmental chemistry ,Biogeochemistry ,chemistry.chemical_element ,Geology ,Trace metal ,Fractionation ,Mercury (element) - Abstract
Mercury (Hg) is a trace metal with potentially serious public health consequences, especially when its neurotoxic form, monomethylmercury (MMHg), accumulates in aquatic and terrestrial food chains. Given the variation in Hg stable isotope abundances (up to 6‰ in δ 202/198 Hg and 11‰ in Δ 201/198 Hg) in natural environmental samples and evidence for Hg isotopic fractionation during microbial (e.g., reduction of Hg(II), degradation and formation of MMHg) and abiotic processes (e.g., photo-degradation of MMHg and volatilization, evaporation and diffusion of Hg(0)), Hg isotope biogeochemistry is currently being developed as a tool to study sources, sinks, and transformations of Hg in the environment. The use of Hg stable isotopes to identify sources of MMHg in aquatic and terrestrial food chains depends on the knowledge of reasonably precise fractionation factors for individual Hg transformations that influence speciation and accumulation of Hg. Microbial transformations are critical to the formation of MMHg and Hg(0) and to the degradation of MMHg. This article a) highlights the importance of experimental determination of microbial fractionation factors for the development of Hg stable isotope systematics because of the limitations of theoretical calculations; b) provides a summary of the current understanding of microbial stable isotope fractionation of Hg, especially during kinetically controlled processes; and c) demonstrates the various factors likely to affect cell-level fractionation during microbial transformations through use of an iterative finite-step model. We also identify future directions, conditions and controls that could help rigorously advance the development of mass-dependent Hg isotope systematics at the enzymatic, cellular and ecosystem level.
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- 2013
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36. Response to Comment on 'Anaerobic Mercury Methylation and Demethylation by Geobacter Bemidjiensis Bem'
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Hui Lin, Tieshan Wang, Xia Lu, Baohua Gu, Alexander Johs, Yu-Rong Liu, Eric M. Pierce, Ziming Yang, Linduo Zhao, Tamar Barkay, Liyuan Liang, and Dwayne A. Elias
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Geobacter bemidjiensis ,Chemistry ,chemistry.chemical_element ,General Chemistry ,Methylation ,010501 environmental sciences ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Mercury (element) ,Biochemistry ,Environmental Chemistry ,Anaerobic exercise ,0105 earth and related environmental sciences ,Demethylation - Published
- 2016
37. Microbial Oxidation of Hg(0) - Its Effect on Hg Stable Isotope Fractionation and Methylmercury Production
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Nathan Yee, John R. Reinfelder, and Tamar Barkay
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biology ,Microorganism ,chemistry.chemical_element ,Cysteine transport ,biology.organism_classification ,Anoxic waters ,Mercury (element) ,chemistry.chemical_compound ,Iron bacteria ,chemistry ,Environmental chemistry ,Anaerobic bacteria ,Shewanella oneidensis ,Methylmercury - Abstract
Mercury (Hg) associated with mixed waste generated by nuclear weapons manufacturing has contaminated vast areas of the Oak Ridge Reservation (ORR). Neurotoxic methylmercury (MeHg) has been formed from the inorganic Hg wastes discharged into headwaters of East Fork Poplar Creek (EFPC). Thus, understanding the processes and mechanisms that lead to Hg methylation along the flow path of EFPC is critical to predicting the impacts of the contamination and the design of remedial action at the ORR. In part I of our project, we investigated Hg(0) oxidation and methylation by anaerobic bacteria. We discovered that the anaerobic bacterium Desulfovibrio desulfuricans ND132 can oxidize elemental mercury [Hg(0)]. When provided with dissolved elemental mercury, D. desulfuricans ND132 converts Hg(0) to Hg(II) and neurotoxic methylmercury [MeHg]. We also demonstrated that diverse species of subsurface bacteria oxidizes dissolved elemental mercury under anoxic conditions. The obligate anaerobic bacterium Geothrix fermentans H5, and the facultative anaerobic bacteria Shewanella oneidensis MR-1 and Cupriavidus metallidurans AE104 can oxidize Hg(0) to Hg(II) under anaerobic conditions. In part II of our project, we established anaerobic enrichment cultures and obtained new bacterial strains from the DOE Oak Ridge site. We isolated three new bacterial strains from subsurface sediments collected from Oak Ridge.more » These isolates are Bradyrhizobium sp. strain FRC01, Clostridium sp. strain FGH, and a novel Negativicutes strain RU4. Strain RU4 is a completely new genus and species of bacteria. We also demonstrated that syntrophic interactions between fermentative bacteria and sulfate-reducing bacteria in Oak Ridge saprolite mediate iron reduction via multiple mechanisms. Finally, we tested the impact of Hg on denitrification in nitrate reducing enrichment cultures derived from subsurface sediments from the Oak Ridge site, where nitrate is a major contaminant. We showed that there is an inverse relationship between Hg concentrations and rates of denitrification in enrichment cultures. In part III of our project, we examined in more detail the effects of microbial interactions on Hg transformations. We discovered that both sulfate reducing and iron reducing bacteria coexist in freshwater sediments and both microbial groups contribute to mercury methylation. We showed that mercury methylation by sulfate reducing and iron reducing bacteria are temporally and spatially separated processes. We also discovered that methanogens can methylate mercury. We showed that Methanospirillum hungatei JF-1 methylated Hg at comparable rates, but with higher yields, than those observed for sulfate-reducing bacteria and iron-reducing bacteria. Finally, we demonstrated that syntrophic interactions between different microbial groups increase mercury methylation rates. We showed that Hg methylation rates are stimulated via inter-species hydrogen and acetate transfer (i) from sulfate-reducing bacteria to methanogens and (ii) from fermenters to the sulfate-reducing bacteria. In part IV of the project, we studied Hg bioavailability and Hg isotope fractionation. We demonstrated that thiol-bound Hg is bioavailable to mercury resistant bacteria. We found that uptake of Hg from Hg-glutathione and Hg-cysteine complexes does not require functioning glutathione and cystine/cysteine transport systems. We demonstrated that a wide range of methylmercury complexes (e.g. MeHgOH, MeHg-cysteine, and MeHg-glutathione) are bioavailable to mercury resistant bacteria. The rate of MeHg demethylation varies more between different species of mercury resistant bacteria than among MeHg complexes. We showed that microbial demethylation of MeHg depends more on the species of microorganism than on the types and relative concentrations of thiols or other MeHg ligands present. Finally, we demonstrated that Hg methylation by Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132 imparts mass-dependent discrimination against 202Hg relative to 198Hg. G. sulfurreducens PCA and D. desulfuricans ND132 have similar kinetic reactant/product Hg fractionation factors. Using the Hg isotope data, we showed that there are multiple intra- and/or extracellular pools provide substrate inorganic Hg for methylation.« less
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- 2016
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38. Microbes in mercury-enriched geothermal springs in western North America
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Susan King, Tamar Barkay, and Gill G. Geesey
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0301 basic medicine ,Environmental Engineering ,Thaumarchaeota ,Microorganism ,030106 microbiology ,chemistry.chemical_element ,Hot Springs ,03 medical and health sciences ,Environmental Chemistry ,Waste Management and Disposal ,Geothermal gradient ,biology ,Bacteria ,Ecology ,Microbiota ,Mercury ,biology.organism_classification ,Pollution ,Archaea ,Mercury (element) ,chemistry ,Metagenomics ,North America ,Metagenome ,Euryarchaeota - Abstract
Because geothermal environments contain mercury (Hg) from natural sources, microorganisms that evolved in these systems have likely adapted to this element. Knowledge of the interactions between microorganisms and Hg in geothermal systems may assist in understanding the long-term evolution of microbial adaptation to Hg with relevance to other environments where Hg is introduced from anthropogenic sources. A number of microbiological studies with supporting geochemistry have been conducted in geothermal systems across western North America. Approximately 1 in 5 study sites include measurements of Hg. Of all prokaryotic taxa reported across sites with microbiological and accompanying physicochemical data, 42% have been detected at sites in which Hg was measured. Genes specifying Hg reduction and detoxification by microorganisms were detected in a number of hot springs across the region. Archaeal-like sequences, representing two crenarchaeal orders and one order each of the Euryarchaeota and Thaumarchaeota, dominated in metagenomes' MerA (the mercuric reductase protein) inventories, while bacterial homologs were mostly found in one deeply sequenced metagenome. MerA homologs were more frequently found in metagenomes of microbial communities in acidic springs than in circumneutral or high pH geothermal systems, possibly reflecting higher bioavailability of Hg under acidic conditions. MerA homologs were found in hot springs prokaryotic isolates affiliated with Bacteria and Archaea taxa. Acidic sites with high Hg concentrations contain more of Archaea than Bacteria taxa, while the reverse appears to be the case in circumneutral and high pH sites with high Hg concentrations. However, MerA was detected in only a small fraction of the Archaea and Bacteria taxa inhabiting sites containing Hg. Nevertheless, the presence of MerA homologs and their distribution patterns in systems, in which Hg has yet to be measured, demonstrates the potential for detoxification by Hg reduction in these geothermal systems, particularly the low pH springs that are dominated by Archaea.
- Published
- 2016
39. Impact of mercury on denitrification and denitrifying microbial communities in nitrate enrichments of subsurface sediments
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Chu-Ching Lin, Ria John, Lee J. Kerkhof, Nathan Yee, Yanping Wang, Tamar Barkay, Heather A. Wiatrowski, and Lily Y. Young
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Geologic Sediments ,Environmental Engineering ,Denitrification ,Firmicutes ,Molecular Sequence Data ,chemistry.chemical_element ,Bioengineering ,Microbiology ,chemistry.chemical_compound ,Denitrifying bacteria ,Bioremediation ,Nitrate ,Environmental Chemistry ,Nitrates ,Bacteria ,biology ,Mercury ,biology.organism_classification ,Pollution ,Mercury (element) ,Terminal restriction fragment length polymorphism ,Biodegradation, Environmental ,chemistry ,Microbial population biology ,Environmental chemistry - Abstract
The contamination of groundwater with mercury (Hg) is an increasing problem worldwide. Yet, little is known about the interactions of Hg with microorganisms and their processes in subsurface environments. We tested the impact of Hg on denitrification in nitrate reducing enrichment cultures derived from subsurface sediments from the Oak Ridge Integrated Field Research Challenge site, where nitrate is a major contaminant and where bioremediation efforts are in progress. We observed an inverse relationship between Hg concentrations and onset and rates of denitrification in nitrate enrichment cultures containing between 53 and 1.1 μM of inorganic Hg; higher Hg concentrations increasingly extended the time to onset of denitrification and inhibited denitrification rates. Microbial community complexity, as indicated by terminal restriction fragment length polymorphism (tRFLP) analysis of the 16S rRNA genes, declined with increasing Hg concentrations; at the 312 nM Hg treatment, a single tRFLP peak was detected representing a culture of Bradyrhizobium sp. that possessed the merA gene indicating a potential for Hg reduction. A culture identified as Bradyrhizobium sp. strain FRC01 with an identical 16S rRNA sequence to that of the enriched peak in the tRFLP patterns, reduced Hg(II) to Hg(0) and carried merA whose amino acid sequence has 97 % identity to merA from the Proteobacteria and Firmicutes. This study demonstrates that in subsurface sediment incubations, Hg may inhibit denitrification and that inhibition may be alleviated when Hg resistant denitrifying Bradyrhizobium spp. detoxify Hg by its reduction to the volatile elemental form.
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- 2012
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40. The effect of mercury on the establishment of Pinus rigida seedlings and the development of their ectomycorrhizal communities
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John Dighton, Tamar Barkay, and Sharron Crane
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Contaminated soils ,Ecology ,biology ,Ecological Modeling ,chemistry.chemical_element ,Plant Science ,Root tip ,biology.organism_classification ,Pinus rigida ,Mercury (element) ,chemistry ,Seedling ,Botany ,Colonization ,Species richness ,Axenic culture ,Ecology, Evolution, Behavior and Systematics - Abstract
Metals are toxic to both plants and fungi, and elevated soil metal concentrations have been documented to change the structure of ectomycorrhizal communities. Mercury (Hg) is a highly toxic metal and inhibits the growth of ectomycorrhizal fungi (ECMF) in axenic culture. However, the effects of Hg on the growth of tree seedlings and the development of their ECMF communities have not been explored. In the current study, Pinus rigida seedlings were planted in soil amended with 0–366 μg g −1 Hg and incubated for 5 months. Survival and growth of P. rigida seedlings was determined, and their ECMF communities were characterized by morphotype analysis. Seedling survival declined with increasing Hg additions, although no reduction in growth was detected among surviving seedlings. The addition of 88 μg g −1 Hg to soil more than halved the total ectomycorrhizal colonization of root tips and reduced both richness and diversity of root tip morphotypes, while lower Hg additions did not significantly affect ECMF community composition relative to the no Hg control. This suggests that changes in the community of ECMF may occur in contaminated soils before any aboveground effects on surviving seedlings are noticeable, potentially altering the contribution of ECMF to the fitness of established host plants.
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- 2012
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41. Employee volunteering: soul, body and CSR
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Tamar Barkay
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business.industry ,media_common.quotation_subject ,Corporate governance ,Public relations ,General Business, Management and Accounting ,Ethnography ,Corporate social responsibility ,Sociology ,Marketing ,Business case ,Dimension (data warehouse) ,Soul ,business ,Human resources ,Social Sciences (miscellaneous) ,media_common ,Qualitative research - Abstract
PurposeBy focusing on the intra‐organization dimension of corporate social responsibility (CSR), this paper aims to offer an ethnographic analysis of the way Coca‐Cola integrates its re‐branding and marketing strategies with CSR and the processes through which this strategic agenda is diffused into the company's national franchise in Israel.Design/methodology/approachThe research is based on a combined qualitative methodology of interviews with managers and employees on all levels of the organization; participant observations of formal meetings, company events and informal gatherings; and document evaluation.FindingsThis paper shows how the CSR program is purposefully and rationally designed to meet the standards of a business case approach to CSR and that, accordingly, company managers integrate it into the activities of departments and divisions such as sales, marketing, and human resources (HR). The paper further shows that the cause‐marketing and product‐branding goals underlying the global re‐branding strategy of Coca‐Cola have been mediated through employee volunteering projects that are based on the recruitment and mobilization of the physical bodies of employees not only as “bodily‐corporate‐producers”, but also as “bodily‐corporate‐ambassadors”.Research limitations/implicationsThe in‐depth empirical research that focused on a single corporation enabled the author to reach a better understanding of the intricate organizational processes involved in the implementation of CSR programs and their effects. At the same time, the research plan lacks a comparative examination of similar processes in other corporations. In this regard, this paper delineates the theoretical and empirical contours for future studies on the actual effects of implementation processes of the business case model for CSR.Originality/valueThe paper enriches a missing part in the literature regarding empirical examination of the impact of CSR at close range and at the level of individual firms.
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- 2012
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42. When Business and Community Meet: A Case Study of Coca-Cola
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Tamar Barkay
- Subjects
Sociology and Political Science ,Community building ,business.industry ,Corporate governance ,Community organization ,media_common.quotation_subject ,Capitalism ,Public relations ,Rhetoric ,Portfolio ,Corporate social responsibility ,Sociology ,business ,Social responsibility ,media_common - Abstract
Community involvement programs occupy centre-stage in the portfolio of many corporations who display and report upon their socially responsible performance. Focusing mainly on issues such as charity and employee volunteering, corporations remain fairly vague in reporting on the way they translate community involvement policies into concrete actions and on the social impact of their community programs. Based on first-hand observations and on-site ethnographic accounts, this study seeks to enrich extant understandings of the character and consequences of corporate involvement in communities. The study follows the diffusion of Coca-Cola’s global branding strategy and the community involvement program it recommended to the Israeli franchisee and analyzes its design and execution on the ground. The study finds a considerable gap between rhetoric of community involvement and practices of mobilizing the community to further the company’s ends. On a theoretical level, the study shows that community programs function as material performances of present-day capitalist ideology.
- Published
- 2011
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43. Methanogens: Principal Methylators of Mercury in Lake Periphyton
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Marc Amyot, Dolors Planas, Tamar Barkay, Stéphanie Hamelin, and Yanping Wang
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010504 meteorology & atmospheric sciences ,chemistry.chemical_element ,RNA, Archaeal ,Euryarchaeota ,010501 environmental sciences ,Methylation ,01 natural sciences ,chemistry.chemical_compound ,RNA, Ribosomal, 16S ,Botany ,Environmental Chemistry ,Sulfate ,Periphyton ,Methylmercury ,0105 earth and related environmental sciences ,Demethylation ,Molybdenum ,biology ,Herbicides ,Sequence Analysis, RNA ,DCMU ,Mercury ,General Chemistry ,Methylmercury Compounds ,biology.organism_classification ,Methanogen ,Anti-Bacterial Agents ,Mercury (element) ,Lakes ,Chloramphenicol ,Alkanesulfonic Acids ,chemistry ,Biofilms ,Diuron ,Water Microbiology ,Water Pollutants, Chemical - Abstract
Mercury methylation and demethylation rates were measured in periphyton biofilms growing on submerged plants from a shallow fluvial lake located along the St. Lawrence River (Quebec, Canada). Incubations were performed in situ within macrophytes beds using low-level spikes of (199)HgO and Me(200)Hg stable isotopes as tracers. To determine which microbial guilds are playing a role in these processes, methylation/demethylation experiments were performed in the absence and presence of different metabolic inhibitors: chloramphenicol (general bacteriostatic inhibitor), molybdate (sodium molybdate, a sulfate reduction inhibitor), BESA (2-bromoethane sulfonic acid, a methanogenesis inhibitor), and DCMU (3-(3,4-dichlorophenyl)-1,1 dimethyl urea, a photosynthesis inhibitor). Active microbes of the periphytic consortium were also characterized using 16S rRNA gene sequencing. Methylation rates in the absence of inhibitors varied from 0.0015 to 0.0180 d(-1) while demethylation rates ranged from 0.083 to 0.217 d(-1), which corresponds to a net methylmercury balance of -0.51 to 1.28 ng gDW periphyton(-1) d(-1). Methylation rates were significantly decreased by half by DCMU and chloramphenicol, totally inhibited by BESA, and were highly stimulated by molybdate. This suggests that methanogens rather than sulfate reducing bacteria were likely the primary methylators in the periphyton of a temperate fluvial lake, a conclusion supported by the detection of 16S rRNA gene sequences that were closely related to those of methanogens. This first clear demonstration of methanogens' role in mercury methylation in environmental periphyton samples expands the known diversity of microbial guilds that contribute to the formation of the neurotoxic substance methylmercury.
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- 2011
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44. Environmental Conditions Constrain the Distribution and Diversity of Archaeal merA in Yellowstone National Park, Wyoming, U.S.A
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John Dighton, Patricia Lu-Irving, Tamar Barkay, David P. Krabbenhoft, Susan King, Sharron Crane, Eric S. Boyd, Yanping Wang, and Gill G. Geesey
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Wyoming ,Sequence analysis ,Soil Science ,Biology ,Hot Springs ,Genes, Archaeal ,03 medical and health sciences ,Microbial ecology ,Phylogenetics ,Dissolved organic carbon ,Phylogeny ,Ecology, Evolution, Behavior and Systematics ,DNA Primers ,030304 developmental biology ,Ecological niche ,0303 health sciences ,Models, Genetic ,Ecology ,030306 microbiology ,National park ,Thermophile ,Biogeochemistry ,Sequence Analysis, DNA ,Archaea ,DNA, Archaeal ,Linear Models ,Oxidoreductases ,Water Microbiology - Abstract
The distribution and phylogeny of extant protein-encoding genes recovered from geochemically diverse environments can provide insight into the physical and chemical parameters that led to the origin and which constrained the evolution of a functional process. Mercuric reductase (MerA) plays an integral role in mercury (Hg) biogeochemistry by catalyzing the transformation of Hg(II) to Hg(0). Putative merA sequences were amplified from DNA extracts of microbial communities associated with mats and sulfur precipitates from physicochemically diverse Hg-containing springs in Yellowstone National Park, Wyoming, using four PCR primer sets that were designed to capture the known diversity of merA. The recovery of novel and deeply rooted MerA lineages from these habitats supports previous evidence that indicates merA originated in a thermophilic environment. Generalized linear models indicate that the distribution of putative archaeal merA lineages was constrained by a combination of pH, dissolved organic carbon, dissolved total mercury and sulfide. The models failed to identify statistically well supported trends for the distribution of putative bacterial merA lineages as a function of these or other measured environmental variables, suggesting that these lineages were either influenced by environmental parameters not considered in the present study, or the bacterial primer sets were designed to target too broad of a class of genes which may have responded differently to environmental stimuli. The widespread occurrence of merA in the geothermal environments implies a prominent role for Hg detoxification in these environments. Moreover, the differences in the distribution of the merA genes amplified with the four merA primer sets suggests that the organisms putatively engaged in this activity have evolved to occupy different ecological niches within the geothermal gradient.
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- 2011
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45. Diversity and characterization of mercury-resistant bacteria in snow, freshwater and sea-ice brine from the High Arctic
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Henrik Skov, Tamar Barkay, Waleed Abu Al-Soud, Søren J. Sørensen, Annette K. Møller, and Niels Kroer
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Ecology ,Firmicutes ,chemistry.chemical_element ,Biology ,biology.organism_classification ,Snow ,Applied Microbiology and Biotechnology ,Microbiology ,Mercury (element) ,chemistry.chemical_compound ,Brine ,Arctic ,chemistry ,Environmental chemistry ,Gammaproteobacteria ,human activities ,Methylmercury ,Bacteria - Abstract
It is well-established that atmospheric deposition transports mercury from lower latitudes to the Arctic. The role of bacteria in the dynamics of the deposited mercury, however, is unknown. We characterized mercury-resistant bacteria from High Arctic snow, freshwater and sea-ice brine. Bacterial densities were 9.4 × 10(5), 5 × 10(5) and 0.9-3.1 × 10(3) cells mL(-1) in freshwater, brine and snow, respectively. Highest cultivability was observed in snow (11.9%), followed by freshwater (0.3%) and brine (0.03%). In snow, the mercury-resistant bacteria accounted for up to 31% of the culturable bacteria, but
- Published
- 2010
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46. A thermophilic bacterial origin and subsequent constraints by redox, light and salinity on the evolution of the microbial mercuric reductase
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K. Kritee, Gill G. Geesey, Tamar Barkay, and Eric S. Boyd
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Marine bacteriophage ,biology ,Phototroph ,Phylogenetics ,Thermophile ,Horizontal gene transfer ,Botany ,Extremophile ,biology.organism_classification ,Microbiology ,Ecology, Evolution, Behavior and Systematics ,Bacteria ,Archaea - Abstract
Mercuric reductase (MerA) is central to the mercury (Hg) resistance (mer) system, catalyzing the reduction of ionic Hg to volatile Hg(0). A total of 213 merA homologues were identified in sequence databases, the majority of which belonged to microbial lineages that occupy oxic environments. merA was absent among phototrophs and in lineages that inhabit anoxic environments. Phylogenetic reconstructions of MerA indicate that (i) merA originated in a thermophilic bacterium following the divergence of the Archaea and Bacteria with a subsequent acquisition in Archaea via horizontal gene transfer (HGT), (ii) HGT of merA was rare across phylum boundaries and (iii) MerA from marine bacteria formed distinct and strongly supported lineages. Collectively, these observations suggest that a combination of redox, light and salinity conditions constrain MerA to microbial lineages that occupy environments where the most oxidized and toxic form of Hg, Hg(II), predominates. Further, the taxon-specific distribution of MerA with and without a 70 amino acid N-terminal extension may reflect intracellular levels of thiols. In conclusion, MerA likely evolved following the widespread oxygenation of the biosphere in a thermal environment and its subsequent evolution has been modulated by the interactions of Hg with the intra- and extracellular environment of the organism.
- Published
- 2010
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47. Mercury methylation in Sphagnum moss mats and its association with sulfate-reducing bacteria in an acidic Adirondack forest lake wetland
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Mark E. Hines, Charles T. Driscoll, Tamar Barkay, Ri Qing Yu, Mario Montesdeoca, and Isaac Adatto
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Peat ,Ecology ,biology ,biology.organism_classification ,Applied Microbiology and Biotechnology ,Microbiology ,Desulfovibrio ,Sphagnum ,Moss ,chemistry.chemical_compound ,chemistry ,Bioaccumulation ,Botany ,Sulfate ,Sulfate-reducing bacteria ,Methylmercury - Abstract
Processes leading to the bioaccumulation of methylmercury (MeHg) in northern wetlands are largely unknown. We have studied various ecological niches within a remote, acidic forested lake ecosystem in the southwestern Adirondacks, NY, to discover that mats comprised of Sphagnum moss were a hot spot for mercury (Hg) and MeHg accumulation (190.5 and 18.6 ng g⁻¹ dw, respectively). Furthermore, significantly higher potential methylation rates were measured in Sphagnum mats as compared with other sites within Sunday Lake's ecosystem. Although MPN estimates showed a low biomass of sulfate-reducing bacteria (SRB), 2.8 × 10⁴ cells mL⁻¹ in mat samples, evidence consisting of (1) a twofold stimulation of potential methylation by the addition of sulfate, (2) a significant decrease in Hg methylation in the presence of the sulfate reduction inhibitor molybdate, and (3) presence of dsrAB-like genes in mat DNA extracts, suggested that SRB were involved in Hg methylation. Sequencing of dsrB genes indicated that novel SRB, incomplete oxidizers including Desulfobulbus spp. and Desulfovibrio spp., and syntrophs dominated the sulfate-reducing guild in the Sphagnum moss mat. Sphagnum, a bryophyte dominating boreal peatlands, and its associated microbial communities appear to play an important role in the production and accumulation of MeHg in high-latitude ecosystems.
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- 2010
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48. Growth responses to and accumulation of mercury by ectomycorrhizal fungi
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John Dighton, Tamar Barkay, and Sharron Crane
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Fungi ,chemistry.chemical_element ,Heavy metals ,Metal toxicity ,Mercury ,Biology ,Contamination ,Ectosymbiosis ,Mercury (element) ,Infectious Diseases ,chemistry ,Mycorrhizae ,Bioaccumulation ,Environmental chemistry ,Botany ,Genetics ,Axenic culture ,Inhibitory effect ,Ecology, Evolution, Behavior and Systematics - Abstract
Heavy metals have been shown to negatively affect the growth of ectomycorrhizal fungi (ECMF). In addition, ECMF have been shown to accumulate heavy metals and to protect host trees from metal toxicity. However, specific literature on the interactions between ECMF and mercury (Hg) is scant. This paper describes the responses of ECMF to Hg in axenic culture conditions. Six ECMF from an area with no known history of direct Hg contamination were tested to determine their sensitivity to Hg. ECMF were incubated on solid medium amended with Hg (0–50 μM) as HgCl 2 and the effect of Hg on radial growth was determined. The effect of preexposure cultivation on Hg sensitivity, the effect of Hg on biomass production, and the ability to accumulate Hg were determined for four of the ECMF. At micromolar concentrations, Hg significantly inhibited the radial growth rate of ECMF. This inhibitory effect was lessened in some ECMF when an established colony was exposed to Hg. Mercury lowered biomass production by some ECMF, and ECMF accumulate Hg from a solid growth substrate in direct relation to the amount of Hg added to the media. Possible implications for ECMF communities in Hg-impacted areas are discussed.
- Published
- 2010
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49. Regulation and voluntarism: A case study of governance in the making
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Tamar Barkay
- Subjects
Delegate ,Public Administration ,Sociology and Political Science ,business.industry ,media_common.quotation_subject ,Corporate governance ,Legislation ,Public administration ,Public relations ,Environmental governance ,State (polity) ,Regulatory capitalism ,Ideology ,Sociology ,Voluntarism (action) ,business ,Law ,media_common - Abstract
In this article I analyze a multi-stakeholder process of environmental regulation. By grounding the article in the literature on regulatory capitalism and governance, I follow the career of a specific legislative process: the enactment of Israel's Deposit Law on Beverage Containers, which aims to delegate the responsibility for recycling to industry. I show that one crucial result of this process was the creation of a non-profit entity licensed to act as a compliance mechanism. This new entity enabled industry to distance itself from the responsibility of recycling, and thereby frustrated the original objective of the legislation, which was to implement the principle of “extended producer responsibility.” Furthermore, this entity, owned by commercial companies and yet acting as an environmentally friendly organization, allowed industry to promote an anti-regulatory agenda via a “civic voice.” The study moves methodologically from considering governance as an institutional structure to analyzing the process of “governancing,” through which authoritative capacities and legal responsibilities are distributed among state and non-state actors. Two key findings are that this process and its outcome (i) are premised on an ideology of civic voluntarism, which ultimately delegates environmental responsibilities to citizens; and (ii) facilitate an anti-regulatory climate that serves commercial interests.
- Published
- 2009
- Full Text
- View/download PDF
50. Reduction of Hg(II) to Hg(0) by Magnetite
- Author
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Nathan Yee, Ravi K. Kukkadapu, Eugene S. Ilton, Tamar Barkay, Heather A. Wiatrowski, and Soumya Das
- Subjects
Reaction mechanism ,X-Rays ,Inorganic chemistry ,chemistry.chemical_element ,Mercury ,General Chemistry ,Hydrogen-Ion Concentration ,Ferric Compounds ,Redox ,Chloride ,Ferrosoferric Oxide ,Mercury (element) ,Chemical kinetics ,Reaction rate ,Spectroscopy, Mossbauer ,chemistry.chemical_compound ,Chlorides ,chemistry ,Mössbauer spectroscopy ,medicine ,Environmental Chemistry ,Oxidation-Reduction ,Magnetite ,medicine.drug - Abstract
Mercury (Hg) is a highly toxic element, and its contamination of groundwater presents a significant threat to terrestrial ecosystems. Understanding the geochemical processes that mediate mercury transformations in the subsurface is necessary to predict its fate and transport. In this study, we investigated the redox transformation of mercuric Hg (Hg[II]) in the presence of the Fe(II)/Fe(III) mixed valence iron oxide mineral magnetite. Kinetic and spectroscopic experiments were performed to elucidate reaction rates and mechanisms. The experimental data demonstrated that reaction of Hg(II) with magnetite resulted in the loss of Hg(II) and the formation of volatile elemental Hg (Hg[0]). Kinetic experiments showed that Hg(II) reduction occurred within minutes, with reaction rates increasing with increasing magnetite surface area (0.5 to 2 m2/L) and solution pH (4.8 to 6.7), and decreasing with increasing chloride concentration (10(-6) to 10(-2) mol/L). Mössbauer spectroscopic analysis of reacted magnetite samples revealed a decrease in Fe(II) content, corresponding to the oxidation of Fe(II) to Fe(III) in the magnetite structure. X-ray photoelectron spectroscopy detected the presence of Hg(II) on magnetite surfaces, implying that adsorption is involved in the electron transfer process. These results suggest that Hg(II) reaction with solid-phase Fe(II) is a kinetically favorable pathway for Hg(II) reduction in magnetite-hearing environmental systems.
- Published
- 2009
- Full Text
- View/download PDF
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