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Zhang L, Wu S, Zhao L, Lu X, Pierce EM, Gu B. Mercury Sorption and Desorption on Organo-Mineral Particulates as a Source for Microbial Methylation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:2426-2433. [PMID: 30702880 DOI: 10.1021/acs.est.8b06020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
In natural freshwater and sediments, mercuric mercury (Hg(II)) is largely associated with particulate minerals and organics, but it remains unclear under what conditions particulates may become a sink or a source for Hg(II) and whether the particulate-bound Hg(II) is bioavailable for microbial uptake and methylation. In this study, we investigated Hg(II) sorption-desorption characteristics on three organo-coated hematite particulates and a Hg-contaminated natural sediment and evaluated the potential of particulate-bound Hg(II) for microbial methylation. Mercury rapidly sorbed onto particulates, especially the cysteine-coated hematite and sediment, with little desorption observed (0.1-4%). However, the presence of Hg-binding ligands, such as low-molecular-weight thiols and humic acids, resulted in up to 60% of Hg(II) desorption from the Hg-laden hematite particulates but <6% from the sediment. Importantly, the particulate-bound Hg(II) was bioavailable for uptake and methylation by a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 under anaerobic incubations, and the methylation rate was 4-10 times higher than the desorption rate of Hg(II). These observations suggest direct contacts and interactions between bacterial cells and the particulate-bound Hg(II), resulting in rapid exchange or uptake of Hg(II) by the bacteria. The results highlight the importance of Hg(II) partitioning at particulate-water interfaces and the role of particulates as a significant source of Hg(II) for methylation in the environment.
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Affiliation(s)
- Lijie Zhang
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Shan Wu
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
- School of Resource, Environmental and Chemical Engineering , Nanchang University , Nanchang 330031 , China
| | - Linduo Zhao
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Xia Lu
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Eric M Pierce
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
| | - Baohua Gu
- Environmental Sciences Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States
- Department of Biosystems Engineering and Soil Science , University of Tennessee , Knoxville , Tennessee 37996 , United States
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52
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Regnell O, Watras CJ. Microbial Mercury Methylation in Aquatic Environments: A Critical Review of Published Field and Laboratory Studies. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:4-19. [PMID: 30525497 DOI: 10.1021/acs.est.8b02709] [Citation(s) in RCA: 103] [Impact Index Per Article: 20.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Methylmercury (MeHg) is an environmental contaminant of concern because it biomagnifies in aquatic food webs and poses a health hazard to aquatic biota, piscivorous wildlife and humans. The dominant source of MeHg to freshwater systems is the methylation of inorganic Hg (IHg) by anaerobic microorganisms; and it is widely agreed that in situ rates of Hg methylation depend on two general factors: the activity of Hg methylators and their uptake of IHg. A large body of research has focused on the biogeochemical processes that regulate these two factors in nature; and studies conducted within the past ten years have made substantial progress in identifying the genetic basis for intracellular methylation and defining the processes that govern the cellular uptake of IHg. Current evidence indicates that all Hg methylating anaerobes possess the gene pair hgcAB that encodes proteins essential for Hg methylation. These genes are found in a large variety of anaerobes, including iron reducers and methanogens; but sulfate reduction is the metabolic process most often reported to show strong links to MeHg production. The uptake of Hg substrate prior to methylation may occur by passive or active transport, or by a combination of both. Competitive inhibition of Hg uptake by Zn speaks in favor of active transport and suggests that essential metal transporters are involved. Shortly after its formation, MeHg is typically released from cells, but the efflux mechanisms are unknown. Although methylation facilitates Hg depuration from the cell, evidence suggests that the hgcAB genes are not induced or favored by Hg contamination. Instead, high MeHg production can be linked to high Hg bioavailability as a result of the formation of Hg(SH)2, HgS nanoparticles, and Hg-thiol complexes. It is also possible that sulfidic conditions require strong essential metal uptake systems that inadvertently bring Hg into the cytoplasm of Hg methylating microbes. In comparison with freshwaters, Hg methylation in open ocean waters appears less restricted to anoxic environments. It does seem to occur mainly in oxygen deficient zones (ODZs), and possibly within anaerobic microzones of settling organic matter, but MeHg (CH3Hg+) and Me2Hg ((CH3)2Hg) have been shown to form also in surface water samples from the euphotic zone. Future studies may disclose whether several different pathways lead to Hg methylation in marine waters and explain why Me2Hg is a significant Hg species in oceans but seemingly not in most freshwaters.
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Affiliation(s)
- Olof Regnell
- Department of Biology/Aquatic Ecology , Lund University , SE-223 62 Lund , Sweden
| | - Carl J Watras
- Bureau of Water Quality , Wisconsin Department of Natural Resources , Madison , Wisconsin 53703 , United States
- Center for Limnology , University of Wisconsin-Madison , 3110 Trout Lake Station Drive , Boulder Junction , Wisconsin 54512 , United States
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53
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Li Y, Li H, Li YF, Zhao J, Guo J, Wang R, Li B, Zhang Z, Gao Y. Evidence for molecular antagonistic mechanism between mercury and selenium in rice (Oryza sativa L.): A combined study using 1, 2-dimensional electrophoresis and SR-XRF techniques. J Trace Elem Med Biol 2018; 50:435-440. [PMID: 29066364 DOI: 10.1016/j.jtemb.2017.10.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Revised: 09/25/2017] [Accepted: 10/13/2017] [Indexed: 11/16/2022]
Abstract
Mercury (Hg) is a hazardous chemical in the environment and can accumulate in the food chain. Selenium (Se) is a necessary element for human health and has antagonistic effects on Hg toxicity. In this work, we investigated the effect of Se on Hg containing and Hg-responsive proteins in rice using 1, 2-dimensional electrophoresis combined with SR-XRF techniques. Two weeks old rice seedlings were exposed to Hg and/or Se compounds. After 21days proteins in the rice roots were separated by electrophoresis and their metal contents were determined by X-ray fluorescence to identify Hg and Se responsive biomolecules. The results show that under Hg stress alone Hg is bound to proteins with molecular weights of 15-25kDa. With the addition of Se, a new Hg-containing protein band in the 55-70kDa range was also found, while the content of Hg in the 15-25kDa proteins decreased. Ten and nine new protein spots were identified after adding Se to inorganic Hg and methylmercury exposed roots, respectively. Adding Se regulates the abundance of proteins associated with carbohydrate and energy metabolism, stress response, cell cycle, and DNA replication indicating that these proteins mediate the antagonism of Se against Hg toxicity. This study helps us to better understand the molecular mechanism of Hg tolerance as well as the molecular antagonism between Hg and Se in rice plants.
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Affiliation(s)
- Yunyun Li
- Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 10049, China; College of Resources and Environment, Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, Fujian Agriculture and Forestry University, Fuzhou 350002, Fujian, China
| | - Hong Li
- Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 10049, China
| | - Yu-Feng Li
- Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 10049, China
| | - Jiating Zhao
- Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 10049, China.
| | - Jingxia Guo
- College of Resources and Environment, Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, Fujian Agriculture and Forestry University, Fuzhou 350002, Fujian, China
| | - Ru Wang
- College of Resources and Environment, Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, Fujian Agriculture and Forestry University, Fuzhou 350002, Fujian, China
| | - Bai Li
- Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 10049, China
| | - Zhiyong Zhang
- Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 10049, China
| | - Yuxi Gao
- Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 10049, China.
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54
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Abstract
Mercury (Hg) is a global pollutant emitted primarily as gaseous Hg0 that is deposited in aquatic and terrestrial ecosystems following its oxidation to HgII. From that point, microbes play a key role in determining Hg’s fate in the environment by participating in sequestration, oxidation, reduction, and methylation reactions. A wide diversity of chemotrophic and phototrophic microbes occupying oxic and anoxic habitats are known to participate directly in Hg cycling. Over the last few years, new findings have come to light that have greatly improved our mechanistic understanding of microbe-mediated Hg cycling pathways in the environment. In this review, we summarize recent advances in microbially mediated Hg cycling and take the opportunity to compare the relatively well-studied chemotrophic pathways to poorly understood phototrophic pathways. We present how the use of genomic and analytical tools can be used to understand Hg transformations and the physiological context of recently discovered cometabolic Hg transformations supported in anaerobes and phototrophs. Finally, we propose a conceptual framework that emphasizes the role that phototrophs play in environmental Hg redox cycling and the importance of better characterizing such pathways in the face of the environmental changes currently underway.
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Affiliation(s)
- Daniel S. Grégoire
- Biology Department, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
| | - Alexandre J. Poulain
- Biology Department, University of Ottawa, 30 Marie Curie, Ottawa, ON K1N 6N5, Canada
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55
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Bouchet S, Goñi-Urriza M, Monperrus M, Guyoneaud R, Fernandez P, Heredia C, Tessier E, Gassie C, Point D, Guédron S, Achá D, Amouroux D. Linking Microbial Activities and Low-Molecular-Weight Thiols to Hg Methylation in Biofilms and Periphyton from High-Altitude Tropical Lakes in the Bolivian Altiplano. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:9758-9767. [PMID: 30037219 DOI: 10.1021/acs.est.8b01885] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
The sources and factors controlling concentrations of monomethylmercury (MMHg) in aquatic ecosystems need to be better understood. Here, we investigated Hg transformations in sediments, periphyton associated with green algae's or aquatic plants, and benthic biofilms from the Lake Titicaca hydrosystem and compared them to the occurrence of active methylating microorganisms and extracellular Hg ligands. Intense Hg methylation was found in benthic biofilms and green algae's periphyton, while it remained low in sediments and aquatic plants' periphyton. Demethylation varied between compartments but remained overall in the same range. Hg methylation was mainly carried out by sulfate reducers, although methanogens also played a role. Its variability between compartments was first explained by the presence or absence of the hgcAB genes. Next, both benthic biofilm and green algae's periphyton exhibited a great diversity of extracellular low-molecular-weight (LMW) thiols (13 or 14 compounds) present at a range of a few nmol L-1 or μmol L-1 but clearly dominated by cysteine and 3-mercaptopropionic acid. Hg methylation was overall positively correlated to the total thiol concentrations, albeit to different extents according to the compartment and conditions. This work is the first examining the interplay between active methylating bacterial communities and extracellular ligands in heterotrophic biofilms and supports the involvement of LMW thiols in Hg methylation in real aquatic systems.
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Affiliation(s)
- Sylvain Bouchet
- CNRS/Univ Pau & Pays Adour , Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux , UMR5254, 64000 , Pau , France
| | - Marisol Goñi-Urriza
- CNRS/Univ Pau & Pays Adour , Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux , UMR5254, 64000 , Pau , France
| | - Mathilde Monperrus
- CNRS/Univ Pau & Pays Adour , Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux , UMR5254, 64000 , Pau , France
| | - Rémy Guyoneaud
- CNRS/Univ Pau & Pays Adour , Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux , UMR5254, 64000 , Pau , France
| | - Pablo Fernandez
- Unidad de Calidad Ambiental (UCA) , Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota , Calle 27 , 00000 La Paz , Bolivia
| | - Carlos Heredia
- Unidad de Calidad Ambiental (UCA) , Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota , Calle 27 , 00000 La Paz , Bolivia
| | - Emmanuel Tessier
- CNRS/Univ Pau & Pays Adour , Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux , UMR5254, 64000 , Pau , France
| | - Claire Gassie
- CNRS/Univ Pau & Pays Adour , Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux , UMR5254, 64000 , Pau , France
| | - David Point
- Unidad de Calidad Ambiental (UCA) , Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota , Calle 27 , 00000 La Paz , Bolivia
- Géosciences Environnement Toulouse, UMR5563, IRD UR 234 , Université Paul Sabatier , 14 Avenue Edouard Belin , 31400 Toulouse , France
| | - Stéphane Guédron
- Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre , 38000 Grenoble , France
- Laboratorio de Hidroquímica , Instituto de Investigaciones Químicas, Universidad Mayor de San Andrés, Campus Universitario de Cota-Cota , casilla 3161 , 00000 La Paz , Bolivia
| | - Dario Achá
- Unidad de Calidad Ambiental (UCA) , Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota , Calle 27 , 00000 La Paz , Bolivia
| | - David Amouroux
- CNRS/Univ Pau & Pays Adour , Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux , UMR5254, 64000 , Pau , France
- Unidad de Calidad Ambiental (UCA) , Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota , Calle 27 , 00000 La Paz , Bolivia
- Géosciences Environnement Toulouse, UMR5563, IRD UR 234 , Université Paul Sabatier , 14 Avenue Edouard Belin , 31400 Toulouse , France
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56
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Thomas SA, Rodby KE, Roth EW, Wu J, Gaillard JF. Spectroscopic and Microscopic Evidence of Biomediated HgS Species Formation from Hg(II)-Cysteine Complexes: Implications for Hg(II) Bioavailability. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:10030-10039. [PMID: 30078312 DOI: 10.1021/acs.est.8b01305] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We investigated the chemistry of Hg(II) during exposure of exponentially growing bacteria ( Escherichia coli, Bacillus subtilis, and Geobacter sulfurreducens) to 50 nM, 500 nM, and 5 μM total Hg(II) with and without added cysteine. With X-ray absorption spectroscopy, we provide direct evidence of the formation of cell-associated HgS for all tested bacteria. The addition of cysteine (100-1000 μM) promotes HgS formation (>70% of total cell-associated Hg(II)) as a result of the biodegradation of added cysteine to sulfide. Cell-associated HgS species are also detected when cysteine is not added as a sulfide source. Two phases of HgS, cinnabar (α-HgS) and metacinnabar (β-HgS), form depending on the total concentration of Hg(II) and sulfide in the exposure medium. However, α-HgS exclusively forms in assays that contain an excess of cysteine. Scanning transmission electron microscopy images reveal that nanoparticulate HgS(s) is primarily located at the cell surface/extracellular matrix of Gram-negative E. coli and G. sulfurreducens and in the cytoplasm/cell membrane of Gram-positive B. subtilis. Intracellular Hg(II) was detected even when the predominant cell-associated species was HgS. This study shows that HgS species can form from exogenous thiol-containing ligands and endogenous sulfide in Hg(II) biouptake assays under nondissimilatory sulfate reducing conditions, providing new considerations for the interpretation of Hg(II) biouptake results.
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Affiliation(s)
- Sara A Thomas
- Department of Civil and Environmental Engineering , Northwestern University , 2145 Sheridan Road , Evanston , Illinois 60208 , United States
| | - Kara E Rodby
- Department of Civil and Environmental Engineering , Northwestern University , 2145 Sheridan Road , Evanston , Illinois 60208 , United States
| | - Eric W Roth
- Department of Materials Science and Engineering, NU ANCE Center , Northwestern University , Evanston , Illinois 60208 , United States
| | - Jinsong Wu
- Department of Materials Science and Engineering, NU ANCE Center , Northwestern University , Evanston , Illinois 60208 , United States
| | - Jean-François Gaillard
- Department of Civil and Environmental Engineering , Northwestern University , 2145 Sheridan Road , Evanston , Illinois 60208 , United States
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57
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Qian C, Chen H, Johs A, Lu X, An J, Pierce EM, Parks JM, Elias DA, Hettich RL, Gu B. Quantitative Proteomic Analysis of Biological Processes and Responses of the Bacterium Desulfovibrio desulfuricans ND132 upon Deletion of Its Mercury Methylation Genes. Proteomics 2018; 18:e1700479. [PMID: 30009483 DOI: 10.1002/pmic.201700479] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Revised: 05/17/2018] [Indexed: 11/10/2022]
Abstract
Recent studies of microbial mercury (Hg) methylation revealed a key gene pair, hgcAB, which is essential for methylmercury (MeHg) production in the environment. However, many aspects of the mechanism and biological processes underlying Hg methylation, as well as any additional physiological functions of the hgcAB genes, remain unknown. Here, quantitative proteomics are used to identify changes in potential functional processes related to hgcAB gene deletion in the Hg-methylating bacterium Desulfovibrio desulfuricans ND132. Global proteomics analyses indicate that the wild type and ΔhgcAB strains are similar with respect to the whole proteome and the identified number of proteins, but differ significantly in the abundance of specific proteins. The authors observe changes in the abundance of proteins related to the glycolysis pathway and one-carbon metabolism, suggesting that the hgcAB gene pair is linked to carbon metabolism. Unexpectedly, the authors find that the deletion of hgcAB significantly impacts a range of metal transport proteins, specifically membrane efflux pumps such as those associated with heavy metal copper (Cu) export, leading to decreased Cu uptake in the ΔhgcAB mutant. This observation indicates possible linkages between this set of proteins and metal homeostasis in the cell. However, hgcAB gene expression is not induced by Hg, as evidenced by similarly low abundance of HgcA and HgcB proteins in the absence or presence of Hg (500 nm). Taken together, these results suggest an apparent link between HgcAB, one-carbon metabolism, and metal homeostasis, thereby providing insights for further exploration of biochemical mechanisms and biological functions of microbial Hg methylation.
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Affiliation(s)
- Chen Qian
- Chemical Sciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA.,Graduate School of Genome Science and Technology, University of Tennessee, 37996 Knoxville, TN, USA
| | - Hongmei Chen
- Environmental Sciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA
| | - Alexander Johs
- Environmental Sciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA
| | - Xia Lu
- Environmental Sciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA
| | - Jing An
- Environmental Sciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA
| | - Eric M Pierce
- Environmental Sciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA
| | - Jerry M Parks
- Biosciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA
| | - Dwayne A Elias
- Biosciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA
| | - Robert L Hettich
- Chemical Sciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA.,Graduate School of Genome Science and Technology, University of Tennessee, 37996 Knoxville, TN, USA
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, TN, USA
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58
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Song Y, Jiang T, Liem-Nguyen V, Sparrman T, Björn E, Skyllberg U. Thermodynamics of Hg(II) Bonding to Thiol Groups in Suwannee River Natural Organic Matter Resolved by Competitive Ligand Exchange, Hg L III-Edge EXAFS and 1H NMR Spectroscopy. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:8292-8301. [PMID: 29983050 DOI: 10.1021/acs.est.8b00919] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A molecular level understanding of the thermodynamics and kinetics of the chemical bonding between mercury, Hg(II), and natural organic matter (NOM) associated thiol functional groups (NOM-RSH) is required if bioavailability and transformation processes of Hg in the environment are to be fully understood. This study provides the thermodynamic stability of the Hg(NOM-RS)2 structure using a robust method in which cysteine (Cys) served as a competing ligand to NOM (Suwannee River 2R101N sample) associated RSH groups. The concentration of the latter was quantified to be 7.5 ± 0.4 μmol g-1 NOM by Hg LIII-edge EXAFS spectroscopy. The Hg(Cys)2 molecule concentration in chemical equilibrium with the Hg(II)-NOM complexes was directly determined by HPLC-ICPMS and losses of free Cys due to secondary reactions with NOM was accounted for in experiments using 1H NMR spectroscopy and 13C isotope labeled Cys. The log K ± SD for the formation of the Hg(NOM-RS)2 molecular structure, Hg2+ + 2NOM-RS- = Hg(NOM-RS)2, and for the Hg(Cys)(NOM-RS) mixed complex, Hg2+ + Cys- + NOM-RS- = Hg(Cys)(NOM-RS), were determined to be 40.0 ± 0.2 and 38.5 ± 0.2, respectively, at pH 3.0. The magnitude of these constants was further confirmed by 1H NMR spectroscopy and the Hg(NOM-RS)2 structure was verified by Hg LIII-edge EXAFS spectroscopy. An important finding is that the thermodynamic stabilities of the complexes Hg(NOM-RS)2, Hg(Cys)(NOM-RS) and Hg(Cys)2 are very similar in magnitude at pH values <7, when all thiol groups are protonated. Together with data on 15 low molecular mass (LMM) thiols, as determined by the same method ( Liem-Ngyuen et al. Thermodynamic stability of mercury(II) complexes formed with environmentally relevant low-molecular-mass thiols studied by competing ligand exchange and density functional theory . Environ. Chem. 2017 , 14 , ( 4 ), 243 - 253 .), the constants for Hg(NOM-RS)2 and Hg(Cys)(NOM-RS) represent an internally consistent thermodynamic data set that we recommend is used in studies where the chemical speciation of Hg(II) is determined in the presence of NOM and LMM thiols.
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Affiliation(s)
- Yu Song
- Department of Forest Ecology and Management , Swedish University of Agricultural Science , SE-901 83 Umeå , Sweden
| | - Tao Jiang
- Department of Forest Ecology and Management , Swedish University of Agricultural Science , SE-901 83 Umeå , Sweden
| | - Van Liem-Nguyen
- Department of Forest Ecology and Management , Swedish University of Agricultural Science , SE-901 83 Umeå , Sweden
- School of Science and Technology , Örebro University , SE-701 82 Örebro , Sweden
| | - Tobias Sparrman
- Department of Chemistry , Umeå University , SE-901 87 Umeå , Sweden
| | - Erik Björn
- Department of Chemistry , Umeå University , SE-901 87 Umeå , Sweden
| | - Ulf Skyllberg
- Department of Forest Ecology and Management , Swedish University of Agricultural Science , SE-901 83 Umeå , Sweden
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59
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Study on Mercury Distribution and Speciation in Urban Road Runoff in Nanjing City, China. WATER 2017. [DOI: 10.3390/w9100779] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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60
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Zhou J, Smith MD, Cooper CJ, Cheng X, Smith JC, Parks JM. Modeling of the Passive Permeation of Mercury and Methylmercury Complexes Through a Bacterial Cytoplasmic Membrane. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:10595-10604. [PMID: 28806072 DOI: 10.1021/acs.est.7b02204] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Cellular uptake and export are important steps in the biotransformation of mercury (Hg) by microorganisms. However, the mechanisms of transport across biological membranes remain unclear. Membrane-bound transporters are known to be relevant, but passive permeation may also be involved. Inorganic HgII and methylmercury ([CH3HgII]+) are commonly complexed with thiolate ligands. Here, we have performed extensive molecular dynamics simulations of the passive permeation of HgII and [CH3HgII]+ complexes with thiolate ligands through a model bacterial cytoplasmic membrane. We find that the differences in free energy between the individual complexes in bulk water and at their most favorable position within the membrane are ∼2 kcal mol-1. We provide a detailed description of the molecular interactions that drive the membrane crossing process. Favorable interactions with carbonyl and tail groups of phospholipids stabilize Hg-containing solutes in the tail-head interface region of the membrane. The calculated permeability coefficients for the neutral compounds CH3S-HgII-SCH3 and CH3HgII-SCH3 are on the order of 10-5 cm s-1. We conclude that small, nonionized Hg-containing species can permeate readily through cytoplasmic membranes.
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Affiliation(s)
- Jing Zhou
- Graduate School of Genome Science and Technology, University of Tennessee , Knoxville, Tennessee 37996, United States
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory , 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
| | - Micholas Dean Smith
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory , 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee , Knoxville, Tennessee 37996, United States
| | - Connor J Cooper
- Graduate School of Genome Science and Technology, University of Tennessee , Knoxville, Tennessee 37996, United States
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory , 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
| | - Xiaolin Cheng
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory , 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee , Knoxville, Tennessee 37996, United States
| | - Jeremy C Smith
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory , 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
- Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee , Knoxville, Tennessee 37996, United States
| | - Jerry M Parks
- Graduate School of Genome Science and Technology, University of Tennessee , Knoxville, Tennessee 37996, United States
- UT/ORNL Center for Molecular Biophysics, Biosciences Division, Oak Ridge National Laboratory , 1 Bethel Valley Road, Oak Ridge, Tennessee 37831-6309, United States
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61
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Zhao L, Chen H, Lu X, Lin H, Christensen GA, Pierce EM, Gu B. Contrasting Effects of Dissolved Organic Matter on Mercury Methylation by Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:10468-10475. [PMID: 28806071 DOI: 10.1021/acs.est.7b02518] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Natural dissolved organic matter (DOM) affects mercury (Hg) redox reactions and anaerobic microbial methylation in the environment. Several studies have shown that DOM can enhance Hg methylation, especially under sulfidic conditions, whereas others show that DOM inhibits Hg methylation due to strong Hg-DOM complexation. In this study, we investigated and compared the effects of DOM on Hg methylation by an iron-reducing bacterium Geobacter sulfurreducens PCA and a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 under nonsulfidic conditions. The methylation experiment was performed with washed cells either in the absence or presence of DOM or glutathione, both of which form strong complexes with Hg via thiol-functional groups. DOM was found to greatly inhibit Hg methylation by G. Sulfurreducens PCA but enhance Hg methylation by D. desulfuricans ND132 cells with increasing DOM concentration. These strain-dependent opposing effects of DOM were also observed with glutathione, suggesting that thiols in DOM likely played an essential role in affecting microbial Hg uptake and methylation. Additionally, DOM and glutathione greatly decreased Hg sorption by G. sulfurreducens PCA but showed little effect on D. desulfuricans ND132 cells, demonstrating that ND132 has a higher affinity to sorb or take up Hg than the PCA strain. These observations indicate that DOM effects on Hg methylation are bacterial strain specific, depend on the DOM:Hg ratio or site-specific conditions, and may thus offer new insights into the role of DOM in methylmercury production in the environment.
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Affiliation(s)
- Linduo Zhao
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Hongmei Chen
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Xia Lu
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Hui Lin
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Geoff A Christensen
- Biosciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Eric M Pierce
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
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Stenzler B, Hinz A, Ruuskanen M, Poulain AJ. Ionic Strength Differentially Affects the Bioavailability of Neutral and Negatively Charged Inorganic Hg Complexes. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:9653-9662. [PMID: 28701033 DOI: 10.1021/acs.est.7b01414] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Mercury (Hg) bioavailability to bacteria in marine systems is the first step toward its bioamplification in food webs. These systems exhibit high salinity and ionic strength that will both alter Hg speciation and properties of the bacteria cell walls. The role of Hg speciation on Hg bioavailability in marine systems has not been teased apart from that of ionic strength on cell wall properties, however. We developed and optimized a whole-cell Hg bioreporter capable of functioning under aerobic and anaerobic conditions and exhibiting no physiological limitations of signal production to changes in ionic strength. We show that ionic strength controls the bioavailability of Hg species, regardless of their charge, possibly by altering properties of the bacterial cell wall. The unexpected anaerobic bioavailability of negatively charged halocomplexes may help explain Hg methylation in marine systems such as the oxygen-deficient zone in the oceanic water column, sea ice or polar snow.
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Affiliation(s)
- Benjamin Stenzler
- Biology Department, University of Ottawa , 30 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
| | - Aaron Hinz
- Biology Department, University of Ottawa , 30 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
| | - Matti Ruuskanen
- Biology Department, University of Ottawa , 30 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
| | - Alexandre J Poulain
- Biology Department, University of Ottawa , 30 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
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63
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Graham AM, Cameron-Burr KT, Hajic HA, Lee C, Msekela D, Gilmour CC. Sulfurization of Dissolved Organic Matter Increases Hg-Sulfide-Dissolved Organic Matter Bioavailability to a Hg-Methylating Bacterium. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:9080-9088. [PMID: 28703002 DOI: 10.1021/acs.est.7b02781] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Reactions of dissolved organic matter (DOM) with aqueous sulfide (termed sulfurization) in anoxic environments can substantially increase DOM's reduced sulfur functional group content. Sulfurization may affect DOM-trace metal interactions, including complexation and metal-containing particle precipitation, aggregation, and dissolution. Using a diverse suite of DOM samples, we found that susceptibility to additional sulfur incorporation via reaction with aqueous sulfide increased with increasing DOM aromatic-, carbonyl-, and carboxyl-C content. The role of DOM sulfurization in enhancing Hg bioavailability for microbial methylation was evaluated under conditions typical of Hg methylation environments (μM sulfide concentrations and low Hg-to-DOM molar ratios). Under the conditions of predicted metacinnabar supersaturation, microbial Hg methylation increased with increasing DOM sulfurization, likely reflecting either effective inhibition of metacinnabar growth and aggregation or the formation of Hg(II)-DOM thiol complexes with high bioavailability. Remarkably, Hg methylation efficiencies with the most sulfurized DOM samples were similar (>85% of total Hg methylated) to that observed in the presence of l-cysteine, a ligand facilitating rapid Hg(II) biouptake and methylation. This suggests that complexes of Hg(II) with DOM thiols have similar bioavailability to Hg(II) complexes with low-molecular-weight thiols. Overall, our results are a demonstration of the importance of DOM sulfurization to trace metal and metalloid (especially mercury) fate in the environment. DOM sulfurization likely represents another link between anthropogenic sulfate enrichment and MeHg production in the environment.
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Affiliation(s)
- Andrew M Graham
- Department of Chemistry, Grinnell College , 1116 Eighth Avenue, Grinnell, Iowa 50112, United States
| | - Keaton T Cameron-Burr
- Department of Chemistry, Grinnell College , 1116 Eighth Avenue, Grinnell, Iowa 50112, United States
| | - Hayley A Hajic
- Department of Chemistry, Grinnell College , 1116 Eighth Avenue, Grinnell, Iowa 50112, United States
| | - Connie Lee
- Department of Chemistry, Grinnell College , 1116 Eighth Avenue, Grinnell, Iowa 50112, United States
| | - Deborah Msekela
- Department of Chemistry, Grinnell College , 1116 Eighth Avenue, Grinnell, Iowa 50112, United States
| | - Cynthia C Gilmour
- Smithsonian Environmental Research Center , 647 Contees Wharf Road, Edgewater, Maryland 21037, United States
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64
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Lu X, Gu W, Zhao L, Farhan Ul Haque M, DiSpirito AA, Semrau JD, Gu B. Methylmercury uptake and degradation by methanotrophs. SCIENCE ADVANCES 2017; 3:e1700041. [PMID: 28580426 PMCID: PMC5451197 DOI: 10.1126/sciadv.1700041] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Accepted: 03/30/2017] [Indexed: 05/22/2023]
Abstract
Methylmercury (CH3Hg+) is a potent neurotoxin produced by certain anaerobic microorganisms in natural environments. Although numerous studies have characterized the basis of mercury (Hg) methylation, no studies have examined CH3Hg+ degradation by methanotrophs, despite their ubiquitous presence in the environment. We report that some methanotrophs, such as Methylosinus trichosporium OB3b, can take up and degrade CH3Hg+ rapidly, whereas others, such as Methylococcus capsulatus Bath, can take up but not degrade CH3Hg+. Demethylation by M. trichosporium OB3b increases with increasing CH3Hg+ concentrations but was abolished in mutants deficient in the synthesis of methanobactin, a metal-binding compound used by some methanotrophs, such as M. trichosporium OB3b. Furthermore, addition of methanol (>5 mM) as a competing one-carbon (C1) substrate inhibits demethylation, suggesting that CH3Hg+ degradation by methanotrophs may involve an initial bonding of CH3Hg+ by methanobactin followed by cleavage of the C-Hg bond in CH3Hg+ by the methanol dehydrogenase. This new demethylation pathway by methanotrophs indicates possible broader involvement of C1-metabolizing aerobes in the degradation and cycling of toxic CH3Hg+ in the environment.
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Affiliation(s)
- Xia Lu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Wenyu Gu
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Linduo Zhao
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Muhammad Farhan Ul Haque
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Alan A. DiSpirito
- Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Jeremy D. Semrau
- Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, MI 48109, USA
| | - Baohua Gu
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
- Corresponding author.
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Thomas SA, Gaillard JF. Cysteine Addition Promotes Sulfide Production and 4-Fold Hg(II)-S Coordination in Actively Metabolizing Escherichia coli. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:4642-4651. [PMID: 28353340 DOI: 10.1021/acs.est.6b06400] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The bacterial uptake of mercury(II), Hg(II), is believed to be energy-dependent and is enhanced by cysteine in diverse species of bacteria under aerobic and anaerobic conditions. To gain insight into this Hg(II) biouptake pathway, we have employed X-ray absorption spectroscopy (XAS) to investigate the relationship between exogenous cysteine, cellular metabolism, cellular localization, and Hg(II) coordination in aerobically respiring Escherichia coli (E. coli). We show that cells harvested in exponential growth phase consistently display mixtures of 2-fold and 4-fold Hg(II) coordination to sulfur (Hg-S2 and Hg-S4), with added cysteine enhancing Hg-S4 formation. In contrast, cells in stationary growth phase or cells treated with a protonophore causing a decrease in cellular ATP predominantly contain Hg-S2, regardless of cysteine addition. Our XAS results favor metacinnabar (β-HgS) as the Hg-S4 species, which we show is associated with both the cell envelope and cytoplasm. Additionally, we observe that added cysteine abiotically oxidizes to cystine and exponentially growing E. coli degrade high cysteine concentrations (100-1000 μM) into sulfide. Thermodynamic calculations confirm that cysteine-induced sulfide biosynthesis can promote the formation of dissolved and particulate Hg(II)-sulfide species. This report reveals new complexities arising in Hg(II) bioassays with cysteine and emphasizes the need for considering changes in chemical speciation as well as growth stage.
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Affiliation(s)
- Sara A Thomas
- Department of Civil and Environmental Engineering, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States
| | - Jean-François Gaillard
- Department of Civil and Environmental Engineering, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208, United States
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