501
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Complete Genome of Geobacter pickeringii G13T, a Metal-Reducing Isolate from Sedimentary Kaolin Deposits. GENOME ANNOUNCEMENTS 2015; 3:3/2/e00038-15. [PMID: 25744992 PMCID: PMC4358379 DOI: 10.1128/genomea.00038-15] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We used PacBio sequencing to assemble the genome of the pristine freshwater isolate Geobacter pickeringii G13(T) into a single 3,618,700-bp circular chromosome polished to 99.999% accuracy (quality value [QV], 50). This isolate shares several features with other Geobacter spp., including genes for degradation of aromatics and an abundance of multiheme c-type cytochromes.
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502
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Si Y, Zou Y, Liu X, Si X, Mao J. Mercury methylation coupled to iron reduction by dissimilatory iron-reducing bacteria. CHEMOSPHERE 2015; 122:206-212. [PMID: 25496739 DOI: 10.1016/j.chemosphere.2014.11.054] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Revised: 11/09/2014] [Accepted: 11/18/2014] [Indexed: 05/03/2023]
Abstract
Iron reduction and mercury methylation by dissimilatory iron-reducing bacteria (DIRB), Geobacter sulfurreducens and Shewanella oneidensis, were studied, and the relationship of mercury methylation coupled to iron reduction was determined. The ability of both bacteria for reducing iron was tested, and Fe(III) reduction occurred with the highest rate when ferric oxyhydroxide was used as a terminal electron acceptor. G. sulfurreducens had proven to mediate the production of methylmercury (MeHg), and a notable increase of MeHg following the addition of inorganic Hg was observed. When the initial concentration of HgCl2 was 500nM, about 177.03nM of MeHg was determined at 8d after G. sulfurreducens inoculation. S. oneidensis was tested negligible for Hg methylation and only 12.06nM of MeHg was determined. Iron reduction could potentially influence Hg methylation rates. The increase in MeHg was consistent with high rate of iron reduction, indicating that Fe(III) reduction stimulated the formation of MeHg. Furthermore, the net MeHg concentration increased at low Fe(III) additions from 1.78 to 3.57mM, and then decreased when the added Fe(III) was high from 7.14 to 17.85mM. The mercury methylation rate was suppressed with high Fe(III) additions, which might have been attributable to mercury complexation and low availability.
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Affiliation(s)
- Youbin Si
- School of Resources and Environment, Anhui Agricultural University, Hefei 230036, China.
| | - Yan Zou
- School of Resources and Environment, Anhui Agricultural University, Hefei 230036, China
| | - Xiaohong Liu
- School of Resources and Environment, Anhui Agricultural University, Hefei 230036, China
| | - Xiongyuan Si
- School of Resources and Environment, Anhui Agricultural University, Hefei 230036, China
| | - Jingdong Mao
- Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529, USA
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503
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McCord SA, Heim WA. Identification and prioritization of management practices to reduce methylmercury exports from wetlands and irrigated agricultural lands. ENVIRONMENTAL MANAGEMENT 2015; 55:725-740. [PMID: 25566831 DOI: 10.1007/s00267-014-0425-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2014] [Accepted: 12/05/2014] [Indexed: 06/04/2023]
Abstract
The Sacramento-San Joaquin Delta's (Delta) beneficial uses for humans and wildlife are impaired by elevated methylmercury (MeHg) concentrations in fish. MeHg is a neurotoxin that bioaccumulates in aquatic food webs. The total maximum daily load (TMDL) implementation plan aimed at reducing MeHg in Delta fish obligates dischargers to conduct MeHg control studies. Over 150 stakeholders collaborated to identify 24 management practices (MPs) addressing MeHg nonpoint sources (NPS) in three categories: biogeochemistry (6), hydrology (14), and soil/vegetation (4). Land uses were divided into six categories: permanently and seasonally flooded wetlands, flooded and irrigated agricultural lands, floodplains, and brackish-fresh tidal marshes. Stakeholders scored MPs based on seven criteria: scientific certainty, costs, MeHg reduction potential, spatial applicability, technical capacity to implement, negative impacts to beneficial uses, and conflicting requirements. Semi-quantitative scoring for MPs applicable to each land use (totaling >400 individual scores) led to consensus-based prioritization. This process relied on practical experience from diverse and accomplished NPS stakeholders and synthesis of 17 previous studies. Results provide a comprehensive, stakeholder-driven prioritization of MPs for wetland and irrigated agricultural land managers. Final prioritization highlights the most promising MPs for practical application and control study, and a secondary set of MPs warranting further evaluation. MPs that address hydrology and soil/vegetation were prioritized because experiences were positive and implementation appeared more feasible. MeHg control studies will need to address the TMDL conundrum that MPs effective at reducing MeHg exports could both exacerbate MeHg exposure and contend with other management objectives on site.
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Affiliation(s)
- Stephen A McCord
- McCord Environmental, Inc., 759 Bianco Court, Davis, CA, 95616, USA,
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504
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Site-directed mutagenesis of HgcA and HgcB reveals amino acid residues important for mercury methylation. Appl Environ Microbiol 2015; 81:3205-17. [PMID: 25724962 DOI: 10.1128/aem.00217-15] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Accepted: 02/24/2015] [Indexed: 11/20/2022] Open
Abstract
Methylmercury is a potent neurotoxin that is produced by anaerobic microorganisms from inorganic mercury by a recently discovered pathway. A two-gene cluster, consisting of hgcA and hgcB, encodes two of the proteins essential for this activity. hgcA encodes a corrinoid protein with a strictly conserved cysteine proposed to be the ligand for cobalt in the corrinoid cofactor, whereas hgcB encodes a ferredoxin-like protein thought to be an electron donor to HgcA. Deletion of either gene eliminates mercury methylation by the methylator Desulfovibrio desulfuricans ND132. Here, site-directed mutants of HgcA and HgcB were constructed to determine amino acid residues essential for mercury methylation. Mutations of the strictly conserved residue Cys93 in HgcA, the proposed ligand for the corrinoid cobalt, to Ala or Thr completely abolished the methylation capacity, but a His substitution produced measurable methylmercury. Mutations of conserved amino acids near Cys93 had various impacts on the methylation capacity but showed that the structure of the putative "cap helix" region harboring Cys93 is crucial for methylation function. In the ferredoxin-like protein HgcB, only one of two conserved cysteines found at the C terminus was necessary for methylation, but either cysteine sufficed. An additional, strictly conserved cysteine, Cys73, was also determined to be essential for methylation. This study supports the previously predicted importance of Cys93 in HgcA for methylation of mercury and reveals additional residues in HgcA and HgcB that facilitate the production of this neurotoxin.
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505
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Perrot V, Bridou R, Pedrero Z, Guyoneaud R, Monperrus M, Amouroux D. Identical Hg isotope mass dependent fractionation signature during methylation by sulfate-reducing bacteria in sulfate and sulfate-free environment. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:1365-73. [PMID: 25564955 DOI: 10.1021/es5033376] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Inorganic mercury (iHg) methylation in aquatic environments is the first step leading to monomethylmercury (MMHg) bioaccumulation in food webs and might play a role in the Hg isotopic composition measured in sediments and organisms. Methylation by sulfate reducing bacteria (SRB) under sulfate-reducing conditions is probably one of the most important sources of MMHg in natural aquatic environments, but its influence on natural Hg isotopic composition remains to be ascertained. In this context, the methylating SRB Desulfovibrio dechloracetivorans (strain BerOc1) was incubated under sulfate reducing and fumarate respiration conditions (SR and FR, respectively) to determine Hg species specific (MMHg and IHg) isotopic composition associated with methylation and demethylation kinetics. Our results clearly establish Hg isotope mass-dependent fractionation (MDF) during biotic methylation (-1.20 to +0.58‰ for δ(202)Hg), but insignificant mass-independent fractionation (MIF) (-0.12 to +0.15‰ for Δ(201)Hg). During the 24h of the time-course experiments Hg isotopic composition in the produced MMHg becomes significantly lighter than the residual IHg after 1.5h and shows similar δ(202)Hg values under both FR and SR conditions at the end of the experiments. This suggests a unique pathway responsible for the MDF of Hg isotopes during methylation by this strain regardless the metabolism of the cells. After 9 h of experiment, significant simultaneous demethylation is occurring in the culture and demethylates preferentially the lighter Hg isotopes of MMHg. Therefore, depending on their methylation/demethylation capacities, SRB communities in natural sulfate reducing conditions likely have a significant and specific influence on the Hg isotope composition of MMHg (MDF) in sediments and aquatic organisms.
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Affiliation(s)
- Vincent Perrot
- Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, CNRS-UPPA-UMR-5254, Hélioparc, 2 Avenue du Président Pierre Angot, Pau, 64053, France
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506
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Korte HL, Saini A, Trotter VV, Butland GP, Arkin AP, Wall JD. Independence of nitrate and nitrite inhibition of Desulfovibrio vulgaris Hildenborough and use of nitrite as a substrate for growth. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2015; 49:924-931. [PMID: 25534748 DOI: 10.1021/es504484m] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Sulfate-reducing microbes, such as Desulfovibrio vulgaris Hildenborough, cause “souring” of petroleum reservoirs through produced sulfide and precipitate heavy metals, either as sulfides or by alteration of the metal reduction state. Thus, inhibitors of these microbes, including nitrate and nitrite ions, are studied in order to limit their impact. Nitrite is a potent inhibitor of sulfate reducers, and it has been suggested that nitrate does not inhibit these microbes directly but by reduction to nitrite, which serves as the ultimate inhibitor. Here we provide evidence that nitrate inhibition of D. vulgaris can be independent of nitrite production. We also show that D. vulgaris can use nitrite as a nitrogen source or terminal electron acceptor for growth. Moreover, we report that use of nitrite as a terminal electron acceptor requires nitrite reductase (nrfA) as a D. vulgaris nrfA mutant cannot respire nitrite but remains capable of utilizing nitrite as a nitrogen source. These results illuminate previously uncharacterized metabolic abilities of D. vulgaris that may allow niche expansion in low-sulfate environments. Understanding these abilities may lead to better control of sulfate-reducing bacteria in industrial settings and more accurate prediction of their interactions in the environment.
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507
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Regnell O, Elert M, Höglund LO, Falk AH, Svensson A. Linking cellulose fiber sediment methyl mercury levels to organic matter decay and major element composition. AMBIO 2014; 43:878-890. [PMID: 24420263 PMCID: PMC4190148 DOI: 10.1007/s13280-013-0487-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Revised: 09/25/2013] [Accepted: 12/16/2013] [Indexed: 05/30/2023]
Abstract
Methylation of mercury (Hg) to highly toxic methyl Hg (MeHg), a process known to occur when organic matter (OM) decomposition leads to anoxia, is considered a worldwide threat to aquatic ecosystems and human health. We measured temporal and spatial variations in sediment MeHg, total Hg (THg), and major elements in a freshwater lagoon in Sweden polluted with Hg-laden cellulose fibers. Fiber decomposition, confined to a narrow surface layer, resulted in loss of carbon (C), uptake of nitrogen (N), phosphorus (P), and sulfur (S), and increased MeHg levels. Notably, fiber decomposition and subsequent erosion of fiber residues will cause buried contaminants to gradually come closer to the sediment-water interface. At an adjacent site where decomposed fiber accumulated, there was a gain in C and a loss of S when MeHg increased. As evidenced by correlation patterns and vertical chemical profiles, reduced S may have fueled C-fixation and Hg methylation at this site.
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Affiliation(s)
- Olof Regnell
- />Department of Biology, Aquatic Ecology, University of Lund, Sölvegatan 37, 223 62 Lund, Sweden
| | - Mark Elert
- />Kemakta Konsult AB, Box 12655, 112 93 Stockholm, Sweden
| | | | - Anna Helena Falk
- />Akvaplan-niva AS, FRAM - High North Research Centre for Climate and the Environment, 9296 Tromsö, Norway
| | - Anders Svensson
- />Environmental Unit, Kalmar County Administration, 391 86 Kalmar, Sweden
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508
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Krey A, Kwan M, Chan HM. In vivo and in vitro changes in neurochemical parameters related to mercury concentrations from specific brain regions of polar bears (Ursus maritimus). ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2014; 33:2463-2471. [PMID: 25264143 DOI: 10.1002/etc.2685] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Revised: 02/27/2014] [Accepted: 07/11/2014] [Indexed: 06/03/2023]
Abstract
Mercury (Hg) has been detected in polar bear brain tissue, but its biological effects are not well known. Relationships between Hg concentrations and neurochemical enzyme activities and receptor binding were assessed in the cerebellum, frontal lobes, and occipital lobes of 24 polar bears collected from Nunavik (Northern Quebec), Canada. The concentration-response relationship was further studied with in vitro experiments using pooled brain homogenate of 12 randomly chosen bears. In environmentally exposed brain samples, there was no correlative relationship between Hg concentration and cholinesterase (ChE) activity or muscarinic acetylcholine receptor (mAChR) binding in any of the 3 brain regions. Monoamine oxidase (MAO) activity in the occipital lobe showed a negative correlative relationship with total Hg concentration. In vitro experiments, however, demonstrated that Hg (mercuric chloride and methylmercury chloride) can inhibit ChE and MAO activities and muscarinic mAChR binding. These results show that Hg can alter neurobiochemical parameters but the current environmental Hg exposure level does have an effect on the neurochemistry of polar bears from northern Canada.
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Affiliation(s)
- Anke Krey
- Natural Resources and Environmental Studies, University of Northern British Columbia, Prince George, British Columbia, Canada
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509
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Carrasco L, Vassileva E. Determination of methylmercury in marine sediment samples: method validation and occurrence data. Anal Chim Acta 2014; 853:167-178. [PMID: 25467456 DOI: 10.1016/j.aca.2014.10.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Revised: 10/13/2014] [Accepted: 10/16/2014] [Indexed: 10/24/2022]
Abstract
The determination of methylmercury (MeHg) in sediment samples is a difficult task due to the extremely low MeHg/THg (total mercury) ratio and species interconversion. Here, we present the method validation of a cost-effective fit-for-purpose analytical procedure for the measurement of MeHg in sediments, which is based on aqueous phase ethylation, followed by purge and trap and hyphenated gas chromatography-pyrolysis-atomic fluorescence spectrometry (GC-Py-AFS) separation and detection. Four different extraction techniques, namely acid and alkaline leaching followed by solvent extraction and evaporation, microwave-assisted extraction with 2-mercaptoethanol, and acid leaching, solvent extraction and back extraction into sodium thiosulfate, were examined regarding their potential to selectively extract MeHg from estuarine sediment IAEA-405 certified reference material (CRM). The procedure based on acid leaching with HNO3/CuSO4, solvent extraction and back extraction into Na2S2O3 yielded the highest extraction recovery, i.e., 94±3% and offered the possibility to perform the extraction of a large number of samples in a short time, by eliminating the evaporation step. The artifact formation of MeHg was evaluated by high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS), using isotopically enriched Me(201)Hg and (202)Hg and it was found to be nonexistent. A full validation approach in line with ISO 17025 and Eurachem guidelines was followed. With this in mind, blanks, selectivity, working range (1-800 pg), linearity (0.9995), recovery (94-96%), repeatability (3%), intermediate precision (4%), limit of detection (0.45 pg) and limit of quantification (0.85 pg) were systematically assessed with CRM IAEA-405. The uncertainty budget was calculated and the major contribution to the combined uncertainty (16.24%, k=2) was found to arise from the uncertainty associated with recovery (74.1%). Demonstration of traceability of measurement results is also presented. The validated measurement procedure was applied to the determination of MeHg incurred in sediments from a highly polluted and scarcely studied area in the Caribbean region.
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Affiliation(s)
- Luis Carrasco
- International Atomic Energy Agency, Department of Nuclear Sciences and Applications, Environment Laboratories, 4 Quai Antoine 1er, MC 98000, Monaco
| | - Emilia Vassileva
- International Atomic Energy Agency, Department of Nuclear Sciences and Applications, Environment Laboratories, 4 Quai Antoine 1er, MC 98000, Monaco.
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510
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Lin H, Morrell-Falvey JL, Rao B, Liang L, Gu B. Coupled mercury-cell sorption, reduction, and oxidation on methylmercury production by Geobacter sulfurreducens PCA. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:11969-76. [PMID: 25268220 DOI: 10.1021/es502537a] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
G. sulfurreducens PCA cells have been shown to reduce, sorb, and methylate Hg(II) species, but it is unclear whether this organism can oxidize and methylate dissolved elemental Hg(0) as shown for Desulfovibrio desulfuricans ND132. Using Hg(II) and Hg(0) separately as Hg sources in washed cell assays in phosphate buffered saline (pH 7.4), we report how cell-mediated Hg reduction and oxidation compete or synergize with sorption, thus affecting the production of toxic methylmercury by PCA cells. Methylation is found to be positively correlated to Hg sorption (r = 0.73) but negatively correlated to Hg reduction (r = -0.62). These reactions depend on the Hg and cell concentrations or the ratio of Hg to cellular thiols (-SH). Oxidation and methylation of Hg(0) are favored at relatively low Hg to cell-SH molar ratios (e.g., <1). Increasing Hg to cell ratios from 0.25 × 10(-19) to 25 × 10(-19) moles-Hg/cell (equivalent to Hg/cell-SH of 0.71 to 71) shifts the major reaction from oxidation to reduction. In the absence of five outer membrane c-type cytochromes, mutant ΔomcBESTZ also shows decreases in Hg reduction and increases in methylation. However, the presence of competing thiol-binding ions such as Zn(2+) leads to increased Hg reduction and decreased methylation. These results suggest that the coupled cell-Hg sorption and redox transformations are important in controlling the rates of Hg uptake and methylation by G. sulfurreducens PCA in anoxic environments.
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Affiliation(s)
- Hui Lin
- Environmental Sciences Division and ‡Biosciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
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511
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Hillesland KL, Lim S, Flowers JJ, Turkarslan S, Pinel N, Zane GM, Elliott N, Qin Y, Wu L, Baliga NS, Zhou J, Wall JD, Stahl DA. Erosion of functional independence early in the evolution of a microbial mutualism. Proc Natl Acad Sci U S A 2014; 111:14822-7. [PMID: 25267659 PMCID: PMC4205623 DOI: 10.1073/pnas.1407986111] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Many species have evolved to function as specialized mutualists, often to the detriment of their ability to survive independently. However, there are few, if any, well-controlled observations of the evolutionary processes underlying the genesis of new mutualisms. Here, we show that within the first 1,000 generations of initiating independent syntrophic interactions between a sulfate reducer (Desulfovibrio vulgaris) and a hydrogenotrophic methanogen (Methanococcus maripaludis), D. vulgaris frequently lost the capacity to grow by sulfate respiration, thus losing the primary physiological attribute of the genus. The loss of sulfate respiration was a consequence of mutations in one or more of three key genes in the pathway for sulfate respiration, required for sulfate activation (sat) and sulfate reduction to sulfite (apsA or apsB). Because loss-of-function mutations arose rapidly and independently in replicated experiments, and because these mutations were correlated with enhanced growth rate and productivity, gene loss could be attributed to natural selection, even though these mutations should significantly restrict the independence of the evolved D. vulgaris. Together, these data present an empirical demonstration that specialization for a mutualistic interaction can evolve by natural selection shortly after its origin. They also demonstrate that a sulfate-reducing bacterium can readily evolve to become a specialized syntroph, a situation that may have often occurred in nature.
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Affiliation(s)
| | - Sujung Lim
- Biological Sciences, University of Washington Bothell, Bothell, WA 98011
| | | | | | - Nicolas Pinel
- Civil and Environmental Engineering, and Institute for Systems Biology, Seattle, WA 98109-5234
| | - Grant M Zane
- Department of Biochemistry, University of Missouri, Columbia, MO 65211
| | | | - Yujia Qin
- Institute for Environmental Genomics and Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK 73019
| | - Liyou Wu
- Institute for Environmental Genomics and Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK 73019
| | - Nitin S Baliga
- Institute for Systems Biology, Seattle, WA 98109-5234; Departments of Biology and Microbiology, Molecular and Cellular Biology Program, University of Washington Seattle, Seattle, WA 98195; Lawrence Berkeley National Laboratory, Berkeley, CA 94720; and
| | - Jizhong Zhou
- Institute for Environmental Genomics and Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK 73019; Earth Science Division, State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China
| | - Judy D Wall
- Department of Biochemistry, University of Missouri, Columbia, MO 65211
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512
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Rex (encoded by DVU_0916) in Desulfovibrio vulgaris Hildenborough is a repressor of sulfate adenylyl transferase and is regulated by NADH. J Bacteriol 2014; 197:29-39. [PMID: 25313388 DOI: 10.1128/jb.02083-14] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Although the enzymes for dissimilatory sulfate reduction by microbes have been studied, the mechanisms for transcriptional regulation of the encoding genes remain unknown. In a number of bacteria the transcriptional regulator Rex has been shown to play a key role as a repressor of genes producing proteins involved in energy conversion. In the model sulfate-reducing microbe Desulfovibrio vulgaris Hildenborough, the gene DVU_0916 was observed to resemble other known Rex proteins. Therefore, the DVU_0916 protein has been predicted to be a transcriptional repressor of genes encoding proteins that function in the process of sulfate reduction in D. vulgaris Hildenborough. Examination of the deduced DVU_0916 protein identified two domains, one a winged helix DNA-binding domain common for transcription factors, and the other a Rossman fold that could potentially interact with pyridine nucleotides. A deletion of the putative rex gene was made in D. vulgaris Hildenborough, and transcript expression studies of sat, encoding sulfate adenylyl transferase, showed increased levels in the D. vulgaris Hildenborough Rex (RexDvH) mutant relative to the parental strain. The RexDvH-binding site upstream of sat was identified, confirming RexDvH to be a repressor of sat. We established in vitro that the presence of elevated NADH disrupted the interaction between RexDvH and DNA. Examination of the 5' transcriptional start site for the sat mRNA revealed two unique start sites, one for respiring cells that correlated with the RexDvH-binding site and a second for fermenting cells. Collectively, these data support the role of RexDvH as a transcription repressor for sat that senses the redox status of the cell.
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513
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Gui D, Yu RQ, Sun Y, Chen L, Tu Q, Mo H, Wu Y. Mercury and selenium in stranded Indo-Pacific humpback dolphins and implications for their trophic transfer in food chains. PLoS One 2014; 9:e110336. [PMID: 25310100 PMCID: PMC4195725 DOI: 10.1371/journal.pone.0110336] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Accepted: 09/18/2014] [Indexed: 11/18/2022] Open
Abstract
As top predators in the Pearl River Estuary (PRE) of China, Indo-Pacific humpback dolphins (Sousa chinensis) are bioindicators for examining regional trends of environmental contaminants in the PRE. We examined samples from stranded S. chinensis in the PRE, collected since 2004, to study the distribution and fate of total mercury (THg), methylmercury (MeHg) and selenium (Se) in the major tissues, in individuals at different ages and their prey fishes from the PRE. This study also investigated the potential protective effects of Se against the toxicities of accumulated THg. Dolphin livers contained the highest concentrations of THg (32.34±58.98 µg g−1 dw) and Se (15.16±3.66 µg g−1 dw), which were significantly different from those found in kidneys and muscles, whereas the highest residue of MeHg (1.02±1.11 µg g−1 dw) was found in dolphin muscles. Concentrations of both THg and MeHg in the liver, kidney and muscle of dolphins showed a significantly positive correlation with age. The biomagnification factors (BMFs) of inorganic mercury (Hginorg) in dolphin livers (350×) and MeHg in muscles (18.7×) through the prey fishes were the highest among all three dolphin tissues, whereas the BMFs of Se were much lower in all dolphin tissues. The lower proportion of MeHg in THg and higher Se/THg ratios in tissues were demonstrated. Our studies suggested that S. chinensis might have the potential to detoxify Hg via the demethylation of MeHg and the formation of tiemannite (HgSe) in the liver and kidney. The lower threshold of hepatic THg concentrations for the equimolar accumulation of Se and Hg in S. chinensis suggests that this species has a greater sensitivity to THg concentrations than is found in striped dolphins and Dall’s porpoises.
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Affiliation(s)
- Duan Gui
- Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou, China
| | - Ri-Qing Yu
- Department of Biology, University of Texas at Tyler, Tyler, Texas, United States of America
| | - Yong Sun
- Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou, China
| | - Laiguo Chen
- Urban Environment and Ecology Research Center, South China Institute of Environmental Sciences (SCIES), Ministry of Environmental Protection, Guangzhou, China
| | - Qin Tu
- Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou, China
| | - Hui Mo
- South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China
| | - Yuping Wu
- Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-Sen University, Guangzhou, China
- * E-mail:
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514
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Randomized open-label pilot study of the influence of probiotics and the gut microbiome on toxic metal levels in Tanzanian pregnant women and school children. mBio 2014; 5:e01580-14. [PMID: 25293764 PMCID: PMC4196227 DOI: 10.1128/mbio.01580-14] [Citation(s) in RCA: 137] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Exposure to environmental toxins is a 21st century global health problem that is often the result of dietary intake. Although efforts are made to reduce dietary toxin levels, they are often unsuccessful, warranting research into novel methods to reduce host exposure. Food-grade microbes that can be delivered to the gastrointestinal tract and that are capable of sequestering toxins present a safe and cost-effective intervention. We sought to investigate the potential for probiotic-supplemented yogurt to lower heavy metal levels in at-risk populations of pregnant women and in children in Mwanza, Tanzania, and to examine the microbiome in relation to toxin levels. Two populations suspected to have high toxic metal exposures were studied. A group of 44 school-aged children was followed over 25 days, and 60 pregnant women were followed over their last two trimesters until birth. A yogurt containing 1010 CFU Lactobacillus rhamnosus GR-1 per 250 g was administered, while control groups received either whole milk or no intervention. Changes in blood metal levels were assessed, and the gut microbiomes of the children were profiled by analyzing 16S rRNA sequencing via the Ion Torrent platform. The children and pregnant women in the study were found to have elevated blood levels of lead and mercury compared to age- and sex-matched Canadians. Consumption of probiotic yogurt had a protective effect against further increases in mercury (3.2 nmol/liter; P = 0.035) and arsenic (2.3 nmol/liter; P = 0.011) blood levels in the pregnant women, but this trend was not statistically significant in the children. Elevated blood lead was associated with increases in Succinivibrionaceae and Gammaproteobacteria relative abundance levels in stool. Probiotic food produced locally represents a nutritious and affordable means for people in some developing countries to counter exposures to toxic metals. Further research and field trials are warranted to explore this approach in countries where communities are located near mining sites and agricultural areas, two types of areas where toxins are likely to be elevated.
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515
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Liu YR, Wang JJ, Zheng YM, Zhang LM, He JZ. Patterns of bacterial diversity along a long-term mercury-contaminated gradient in the paddy soils. MICROBIAL ECOLOGY 2014; 68:575-583. [PMID: 24827389 DOI: 10.1007/s00248-014-0430-5] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Accepted: 05/01/2014] [Indexed: 06/03/2023]
Abstract
Mercury (Hg) pollution is usually regarded as an environmental stress in reducing microbial diversity and altering bacterial community structure. However, these results were based on relatively short-term studies, which might obscure the real response of microbial species to Hg contamination. Here, we analysed the bacterial abundance and community composition in paddy soils that have been potentially contaminated by Hg for more than 600 years. Expectedly, the soil Hg pollution significantly influenced the bacterial community structure. However, the bacterial abundance was significantly correlated with the soil organic matter content rather than the total Hg (THg) concentration. The bacterial alpha diversity increased at relatively low levels of THg and methylmercury (MeHg) and subsequently approached a plateau above 4.86 mg kg(-1) THg or 18.62 ng g(-1) MeHg, respectively. Contrasting with the general prediction of decreasing diversity along Hg stress, our results seem to be consistent with the intermediate disturbance hypotheses with the peak biological diversity under intermediate disturbance or stress. This result was partly supported by the inconsistent response of bacterial species to Hg stress. For instance, the relative abundance of Nitrospirae decreased, while that of Gemmatimonadetes increased significantly along the increasing soil THg and MeHg concentrations. In addition, the content of SO(4)(2-), THg, MeHg and soil depth were the four main factors influencing bacterial community structures based on the canonical correspondence analysis (CCA). Overall, our findings provide novel insight into the distribution patterns of bacterial community along the long-term Hg-contaminated gradient in paddy soils.
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Affiliation(s)
- Yu-Rong Liu
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China
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516
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Schaefer JK, Kronberg RM, Morel FMM, Skyllberg U. Detection of a key Hg methylation gene, hgcA, in wetland soils. ENVIRONMENTAL MICROBIOLOGY REPORTS 2014; 6:441-7. [PMID: 25646534 DOI: 10.1111/1758-2229.12136] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The corrinoid protein, HgcA has been shown to be essential for Hg methylation in anaerobic bacteria. We investigated the diversity of hgcA from temperate and tropical wetland soils where Hg methylation is demonstrated. Sequences obtained from both environments clustered with those from the δ-Proteobacteria, Chloroflexi and Methanomicrobia with significant overlap in hgcA phylogeny between libraries. Clear differences in hgcA distribution were observed between two highly contrasting sites within a tropical wetland in Everglades National Park, USA. hgcA sequences obtained from the northern site clustered primarily with those of methanogens, while sequences from the estuarine site clustered primarily with sulphate-reducing bacteria and syntrophs in the δ-Proteobacteria. Libraries obtained from soils collected from a temperate swamp in Sweden were dominated by hgcA sequences within the δ-Proteobacteria with hgcA sequences clustering primarily with iron reducers in the upstream portion of the swamp and with sulphate reducers in the downstream portion of the swamp. Interestingly, enrichments prepared from the lower portion of this temperate wetland contained a high abundance of hgcA sequences clustering with methanogens. This first report on hgcA diversity in environmental samples suggests a role in Hg methylation for various phenotypic groups in different portions of wetlands.
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517
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Bone SE, Bargar JR, Sposito G. Mackinawite (FeS) reduces mercury(II) under sulfidic conditions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:10681-10689. [PMID: 25180562 PMCID: PMC4167055 DOI: 10.1021/es501514r] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2014] [Revised: 08/12/2014] [Accepted: 08/16/2014] [Indexed: 05/30/2023]
Abstract
Mercury (Hg) is a toxicant of global concern that accumulates in organisms as methyl Hg. The production of methyl Hg by anaerobic bacteria may be limited in anoxic sediments by the sequestration of divalent Hg [Hg(II)] into a solid phase or by the formation of elemental Hg [Hg(0)]. We tested the hypothesis that nanocrystalline mackinawite (tetragonal FeS), which is abundant in sediments where Hg is methylated, both sorbs and reduces Hg(II). Mackinawite suspensions were equilibrated with dissolved Hg(II) in batch reactors. Examination of the solid phase using Hg LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy showed that Hg(II) was indeed reduced in FeS suspensions. Measurement of purgeable Hg using cold vapor atomic fluorescence spectrometry (CVAFS) from FeS suspensions and control solutions corroborated the production of Hg(0) that was observed spectroscopically. However, a fraction of the Hg(II) initially added to the suspensions remained in the divalent state, likely in the form of β-HgS-like clusters associated with the FeS surface or as a mixture of β-HgS and surface-associated species. Complexation by dissolved S(-II) in anoxic sediments hinders Hg(0) formation, but, by contrast, Hg(II)-S(-II) species are reduced in the presence of mackinawite, producing Hg(0) after only 1 h of reaction time. The results of our work support the idea that Hg(0) accounts for a significant fraction of the total Hg in wetland and estuarine sediments.
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Affiliation(s)
- Sharon E. Bone
- Environmental
Science, Policy, and Management, University
of California, Berkeley, California 94720, United States
- Geochemistry,
Earth Sciences Division, Lawrence Berkeley
National Laboratory, Berkeley, California 94720, United States
| | - John R. Bargar
- Stanford
Synchrotron Radiation Lightsource, SLAC, 2575 Sand Hill Road, Menlo
Park, California 94025, United States
| | - Garrison Sposito
- Environmental
Science, Policy, and Management, University
of California, Berkeley, California 94720, United States
- Geochemistry,
Earth Sciences Division, Lawrence Berkeley
National Laboratory, Berkeley, California 94720, United States
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518
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Bravo AG, Le Faucheur S, Monperrus M, Amouroux D, Slaveykova VI. Species-specific isotope tracers to study the accumulation and biotransformation of mixtures of inorganic and methyl mercury by the microalga Chlamydomonas reinhardtii. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2014; 192:212-215. [PMID: 24932531 DOI: 10.1016/j.envpol.2014.05.013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Revised: 04/30/2014] [Accepted: 05/09/2014] [Indexed: 06/03/2023]
Abstract
The present study demonstrates that species-specific isotope tracing is an useful tool to precisely measure Hg accumulation and transformations capabilities of living organisms at concentrations naturally encountered in the environment. To that end, a phytoplanktonic green alga Chlamydomonas reinhardtii Dangeard (Chlamydomonadales, Chlorophyceae) was exposed to mixtures of (199)-isotopically enriched inorganic mercury ((199)IHg) and of (201)-isotopically enriched monomethylmercury ((201)CH3Hg) at a concentration range between less than 1 pM to 4 nM. Additionally, one exposure concentration of both mercury species was also studied separately to evaluate possible interactive effects. No difference in the intracellular contents was observed for algae exposed to (199)IHg and (201)CH3Hg alone or in their mixture, suggesting similar accumulation capacity for both species at the studied concentrations. Demethylation of (201)CH3Hg was observed at the highest exposure concentrations, whereas no methylation was detected.
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Affiliation(s)
- Andrea Garcia Bravo
- University of Geneva, Earth and Environment Sciences, Institute F.-A. Forel, 10 route de Suisse, CP 416, CH-1290 Versoix, Switzerland.
| | - Séverine Le Faucheur
- University of Geneva, Earth and Environment Sciences, Institute F.-A. Forel, 10 route de Suisse, CP 416, CH-1290 Versoix, Switzerland
| | - Mathilde Monperrus
- Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, Institut des Sciences Analytiques et de Physico-chimie pour l'Environnement et les Matériaux, IPREM UMR 5254 CNRS - Université de Pau et des Pays de l'Adour, Hélioparc, 2, Avenue Pierre Angot, 64053 Pau Cedex, France
| | - David Amouroux
- Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, Institut des Sciences Analytiques et de Physico-chimie pour l'Environnement et les Matériaux, IPREM UMR 5254 CNRS - Université de Pau et des Pays de l'Adour, Hélioparc, 2, Avenue Pierre Angot, 64053 Pau Cedex, France
| | - Vera I Slaveykova
- University of Geneva, Earth and Environment Sciences, Institute F.-A. Forel, 10 route de Suisse, CP 416, CH-1290 Versoix, Switzerland.
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519
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Jonsson S, Skyllberg U, Nilsson MB, Lundberg E, Andersson A, Björn E. Differentiated availability of geochemical mercury pools controls methylmercury levels in estuarine sediment and biota. Nat Commun 2014; 5:4624. [DOI: 10.1038/ncomms5624] [Citation(s) in RCA: 121] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Accepted: 07/08/2014] [Indexed: 11/09/2022] Open
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520
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Syntrophs dominate sequences associated with the mercury methylation-related gene hgcA in the water conservation areas of the Florida Everglades. Appl Environ Microbiol 2014; 80:6517-26. [PMID: 25107983 DOI: 10.1128/aem.01666-14] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The mechanisms and rates of mercury methylation in the Florida Everglades are of great concern because of potential adverse impacts on human and wildlife health through mercury accumulation in aquatic food webs. We developed a new PCR primer set targeting hgcA, a gene encoding a corrinoid protein essential for Hg methylation across broad phylogenetic boundaries, and used this primer set to study the distribution of hgcA sequences in soils collected from three sites along a gradient in sulfate and nutrient concentrations in the northern Everglades. The sequences obtained were distributed in diverse phyla, including Proteobacteria, Chloroflexi, Firmicutes, and Methanomicrobia; however, hgcA clone libraries from all sites were dominated by sequences clustering within the order Syntrophobacterales of the Deltaproteobacteria (49 to 65% of total sequences). dsrB mRNA sequences, representing active sulfate-reducing prokaryotes at the time of sampling, obtained from these sites were also dominated by Syntrophobacterales (75 to 89%). Laboratory incubations with soils taken from the site low in sulfate concentrations also suggested that Hg methylation activities were primarily mediated by members of the order Syntrophobacterales, with some contribution by methanogens, Chloroflexi, iron-reducing Geobacter, and non-sulfate-reducing Firmicutes inhabiting the sites. This suggests that prokaryotes distributed within clades defined by syntrophs are the predominant group controlling methylation of Hg in low-sulfate areas of the Everglades. Any strategy for managing mercury methylation in the Everglades should consider that net mercury methylation is not limited to the action of sulfate reduction.
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521
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Maccario L, Vogel TM, Larose C. Potential drivers of microbial community structure and function in Arctic spring snow. Front Microbiol 2014; 5:413. [PMID: 25147550 PMCID: PMC4124603 DOI: 10.3389/fmicb.2014.00413] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Accepted: 07/21/2014] [Indexed: 01/31/2023] Open
Abstract
The Arctic seasonal snowpack can extend at times over a third of the Earth’s land surface. This chemically dynamic environment interacts constantly with different environmental compartments such as atmosphere, soil and meltwater, and thus, strongly influences the entire biosphere. However, the microbial community associated with this habitat remains poorly understood. Our objective was to investigate the functional capacities, diversity and dynamics of the microorganisms in snow and to test the hypothesis that their functional signature reflects the snow environment. We applied a metagenomic approach to nine snow samples taken over 2 months during the spring season. Fungi, Bacteroidetes, and Proteobacteria were predominant in metagenomic datasets and changes in community structure were apparent throughout the field season. Functional data that strongly correlated with chemical parameters like mercury or nitrogen species supported that this variation could be explained by fluctuations in environmental conditions. Through inter-environmental comparisons we examined potential drivers of snowpack microbial community functioning. Known cold adaptations were detected in all compared environments without any apparent differences in their relative abundance, implying that adaptive mechanisms related to environmental factors other than temperature may play a role in defining the snow microbial community. Photochemical reactions and oxidative stress seem to be decisive parameters in structuring microbial communities inside Arctic snowpacks.
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Affiliation(s)
- Lorrie Maccario
- CNRS UMR 5005, Environmental Microbial Genomics, Laboratoire Ampère, École Centrale de Lyon, Université de Lyon Ecully, France
| | - Timothy M Vogel
- CNRS UMR 5005, Environmental Microbial Genomics, Laboratoire Ampère, École Centrale de Lyon, Université de Lyon Ecully, France
| | - Catherine Larose
- CNRS UMR 5005, Environmental Microbial Genomics, Laboratoire Ampère, École Centrale de Lyon, Université de Lyon Ecully, France
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522
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Rothenberg SE, Windham-Myers L, Creswell JE. Rice methylmercury exposure and mitigation: a comprehensive review. ENVIRONMENTAL RESEARCH 2014; 133:407-23. [PMID: 24972509 PMCID: PMC4119557 DOI: 10.1016/j.envres.2014.03.001] [Citation(s) in RCA: 119] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2013] [Revised: 01/25/2014] [Accepted: 03/01/2014] [Indexed: 05/20/2023]
Abstract
Rice cultivation practices from field preparation to post-harvest transform rice paddies into hot spots for microbial mercury methylation, converting less-toxic inorganic mercury to more-toxic methylmercury, which is likely translocated to rice grain. This review includes 51 studies reporting rice total mercury and/or methylmercury concentrations, based on rice (Orzya sativa) cultivated or purchased in 15 countries. Not surprisingly, both rice total mercury and methylmercury levels were significantly higher in polluted sites compared to non-polluted sites (Wilcoxon rank sum, p<0.001). However, rice percent methylmercury (of total mercury) did not differ statistically between polluted and non-polluted sites (Wilcoxon rank sum, p=0.35), suggesting comparable mercury methylation rates in paddy soil across these sites and/or similar accumulation of mercury species for these rice cultivars. Studies characterizing the effects of rice cultivation under more aerobic conditions were reviewed to determine the mitigation potential of this practice. Rice management practices utilizing alternating wetting and drying (instead of continuous flooding) caused soil methylmercury levels to spike, resulting in a strong methylmercury pulse after fields were dried and reflooded; however, it is uncertain whether this led to increased translocation of methylmercury from paddy soil to rice grain. Due to the potential health risks, it is advisable to investigate this issue further, and to develop separate water management strategies for mercury polluted and non-polluted sites, in order to minimize methylmercury exposure through rice ingestion.
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Affiliation(s)
- Sarah E Rothenberg
- University of South Carolina, Arnold School of Public Health, Department of Environmental Health Sciences, 921 Assembly Street, Room 401, Columbia, SC 29208, USA.
| | | | - Joel E Creswell
- Brooks Rand Instruments, 4415 6th Ave NW, Seattle, WA 98107, USA.
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523
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Llop S, Murcia M, Aguinagalde X, Vioque J, Rebagliato M, Cases A, Iñiguez C, Lopez-Espinosa MJ, Amurrio A, Navarrete-Muñoz EM, Ballester F. Exposure to mercury among Spanish preschool children: trend from birth to age four. ENVIRONMENTAL RESEARCH 2014; 132:83-92. [PMID: 24747554 DOI: 10.1016/j.envres.2014.03.023] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Revised: 03/06/2014] [Accepted: 03/19/2014] [Indexed: 06/03/2023]
Abstract
The purpose of this study is to describe the total hair mercury concentrations and their determinants in preschool Spanish children, as well as to explore the trend in mercury exposure from birth to the age four. This evolution has been scarcely studied in other birth cohort studies. The study population was 580 four year old children participating in the INMA (i.e. Childhood and Environment) birth cohort study in Valencia (2008-2009). Total mercury concentration at age four was measured in hair samples by atomic absorption spectrometry. Fish consumption and other covariates were obtained by questionnaire. Multivariate linear regression models were conducted in order to explore the association between mercury exposure and fish consumption, socio-demographic characteristics and prenatal exposure to mercury. The geometric mean was 1.10 µg/g (95%CI: 1.02, 1.19). Nineteen percent of children had mercury concentrations above the equivalent to the Provisional Tolerable Weekly Intake proposed by WHO. Mercury concentration was associated with increasing maternal age, fish consumption and cord blood mercury levels, as well as decreasing parity. Children whose mothers worked had higher mercury levels than those with non working mothers. Swordfish, lean fish and canned fish were the fish categories most associated with hair mercury concentrations. We observed a decreasing trend in mercury concentrations between birth and age four. In conclusion, the children participating in this study had high hair mercury concentrations compared to reported studies on children from other European countries and similar to other countries with high fish consumption. The INMA study design allows the evaluation of the exposure to mercury longitudinally and enables this information to be used for biomonitoring purposes and dietary recommendations.
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Affiliation(s)
- Sabrina Llop
- Foundation for the Promotion of Health and Biomedical Research in the Valencian Region, FISABIO-Public Health, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain.
| | - Mario Murcia
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Foundation for the Promotion of Health and Biomedical Research in the Valencian Region, FISABIO-Public Health, Av. Catalunya 21, 46020 Valencia, Spain
| | - Xabier Aguinagalde
- Laboratorio de Salud Pública de Alava, Santiago 11, 01002 Vitoria Gasteiz, Spain
| | - Jesus Vioque
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Universidad Miguel Hernandez, Avenida de Alicante KM 87, 03550 Sant Joan d´Alacant, Spain
| | - Marisa Rebagliato
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Medicine Department, Jaume I University, Av. Vicent Sos Baynat, s/n, 12071 Castelló de la Plana, Spain
| | - Amparo Cases
- Foundation for the Promotion of Health and Biomedical Research in the Valencian Region, FISABIO-Public Health, Av. Catalunya 21, 46020 Valencia, Spain
| | - Carmen Iñiguez
- Foundation for the Promotion of Health and Biomedical Research in the Valencian Region, FISABIO-Public Health, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain
| | - Maria-Jose Lopez-Espinosa
- Foundation for the Promotion of Health and Biomedical Research in the Valencian Region, FISABIO-Public Health, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain
| | - Ascensión Amurrio
- Laboratorio de Salud Pública de Alava, Santiago 11, 01002 Vitoria Gasteiz, Spain
| | - Eva María Navarrete-Muñoz
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Universidad Miguel Hernandez, Avenida de Alicante KM 87, 03550 Sant Joan d´Alacant, Spain
| | - Ferran Ballester
- Foundation for the Promotion of Health and Biomedical Research in the Valencian Region, FISABIO-Public Health, Av. Catalunya 21, 46020 Valencia, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain; Faculty of Nursing, University of Valencia, Jaume Roig s/n, 46010 Valencia, Spain
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524
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Hu X, Mu L, Lu K, Kang J, Zhou Q. Green synthesis of low-toxicity graphene-fulvic acid with an open band gap enhances demethylation of methylmercury. ACS APPLIED MATERIALS & INTERFACES 2014; 6:9220-9227. [PMID: 24853303 DOI: 10.1021/am501334j] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The demethylation of methylmercury has received substantial attention. Here, a novel chemical method for the demethylation of methylmercury is proposed. The low-toxicity graphene-fulvic acid (FA, a ubiquitous material in the environment) was synthesized without the use of a chemical reagent. The hybridized graphene-FA presented an indirect open band gap of 2.25-2.87 eV as well as adequate aqueous dispersion. More importantly, the hybridized graphene-FA exhibited 6- and 10-fold higher photocatalytic efficiencies for the demethylation of methylmercury than FA and free FA with graphene, respectively. This result implies that immobilized, rather than free, FA accelerated the catalysis. Furthermore, inorganic mercuric ion, elemental mercury, and mercuric oxide were identified as the primary demethylation products. For free FA with graphene, graphene quenches the excited-state FA, inhibiting the demethylation by electron transfer. In contrast, the graphene of the self-assembled graphene-FA serves as an electron reservoir, causing electron-hole pair separation. Graphene-FA showed a negligible toxicity toward microalgae compared to graphene. The above results reveal that the green synthesis of graphene and organic molecules is a convenient strategy for obtaining effective cocatalysts.
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Affiliation(s)
- Xiangang Hu
- Key Laboratory of Pollution Processes and Environmental Criteria (Ministry of Education), Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University , Tianjin 300071, China
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525
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Alpers CN, Fleck JA, Marvin-DiPasquale M, Stricker CA, Stephenson M, Taylor HE. Mercury cycling in agricultural and managed wetlands, Yolo Bypass, California: spatial and seasonal variations in water quality. THE SCIENCE OF THE TOTAL ENVIRONMENT 2014; 484:276-87. [PMID: 24332791 DOI: 10.1016/j.scitotenv.2013.10.096] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2012] [Revised: 10/25/2013] [Accepted: 10/27/2013] [Indexed: 05/21/2023]
Abstract
The seasonal and spatial variability of water quality, including mercury species, was evaluated in agricultural and managed, non-agricultural wetlands in the Yolo Bypass Wildlife Area, an area managed for multiple beneficial uses including bird habitat and rice farming. The study was conducted during an 11-month period (June 2007 to April 2008) that included a summer growing season and flooded conditions during winter. Methylmercury (MeHg) concentrations in surface water varied over a wide range (0.1 to 37ngL(-1) unfiltered; 0.04 to 7.3ngL(-1) filtered). Maximum MeHg values are among the highest ever recorded in wetlands. Highest MeHg concentrations in unfiltered surface water were observed in drainage from wild rice fields during harvest (September 2007), and in white rice fields with decomposing rice straw during regional flooding (February 2008). The ratio of MeHg to total mercury (MeHg/THg) increased about 20-fold in both unfiltered and filtered water during the growing season (June to August 2007) in the white and wild rice fields, and about 5-fold in fallow fields (July to August 2007), while there was little to no change in MeHg/THg in the permanent wetland. Sulfate-bearing fertilizer had no effect on Hg(II) methylation, as sulfate-reducing bacteria were not sulfate-limited in these agricultural wetlands. Concentrations of MeHg in filtered and unfiltered water correlated with filtered Fe, filtered Mn, DOC, and two indicators of sulfate reduction: the SO4(2-)/Cl(-) ratio, and δ(34)S in aqueous sulfate. These relationships suggest that microbial reduction of SO4(2-), Fe(III), and possibly Mn(IV) may contribute to net Hg(II)-methylation in this setting.
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Affiliation(s)
- Charles N Alpers
- U.S. Geological Survey, Placer Hall, 6000 J St., Sacramento, CA 95819, United States.
| | - Jacob A Fleck
- U.S. Geological Survey, Placer Hall, 6000 J St., Sacramento, CA 95819, United States.
| | - Mark Marvin-DiPasquale
- U.S. Geological Survey, 345 Middlefield Road, Mailstop 480, Menlo Park, CA 94025, United States.
| | - Craig A Stricker
- U.S. Geological Survey, Fort Collins Science Center, Building 21, Mailstop 963, Denver, CO 80225, United States.
| | - Mark Stephenson
- Moss Landing Marine Laboratory, Moss Landing, CA 95039, United States.
| | - Howard E Taylor
- U.S. Geological Survey, 3215 Marine St., Suite E-127, Boulder, CO 80303, United States.
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526
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Llop S, Engström K, Ballester F, Franforte E, Alhamdow A, Pisa F, Tratnik JS, Mazej D, Murcia M, Rebagliato M, Bustamante M, Sunyer J, Sofianou-Katsoulis Α, Prasouli A, Antonopoulou E, Antoniadou I, Nakou S, Barbone F, Horvat M, Broberg K. Polymorphisms in ABC transporter genes and concentrations of mercury in newborns--evidence from two Mediterranean birth cohorts. PLoS One 2014; 9:e97172. [PMID: 24831289 PMCID: PMC4022503 DOI: 10.1371/journal.pone.0097172] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Accepted: 04/16/2014] [Indexed: 11/19/2022] Open
Abstract
Background The genetic background may influence methylmercury (MeHg) metabolism and neurotoxicity. ATP binding cassette (ABC) transporters actively transport various xenobiotics across biological membranes. Objective To investigate the role of ABC polymorphisms as modifiers of prenatal exposure to MeHg. Methods The study population consisted of participants (n = 1651) in two birth cohorts, one in Italy and Greece (PHIME) and the other in Spain (INMA). Women were recruited during pregnancy in Italy and Spain, and during the perinatal period in Greece. Total mercury concentrations were measured in cord blood samples by atomic absorption spectrometry. Maternal fish intake during pregnancy was determined from questionnaires. Polymorphisms (n = 5) in the ABC genes ABCA1, ABCB1, ABCC1 and ABCC2 were analysed in both cohorts. Results ABCB1 rs2032582, ABCC1 rs11075290, and ABCC2 rs2273697 modified the associations between maternal fish intake and cord blood mercury concentrations. The overall interaction coefficient between rs2032582 and log2-transformed fish intake was negative for carriers of GT (β = −0.29, 95%CI −0.47, −0.12) and TT (β = −0.49, 95%CI −0.71, −0.26) versus GG, meaning that for a doubling in fish intake of the mothers, children with the rs2032582 GG genotype accumulated 35% more mercury than children with TT. For rs11075290, the interaction coefficient was negative for carriers of TC (β = −0.12, 95%CI −0.33, 0.09), and TT (β = −0.28, 95%CI −0.51, −0.06) versus CC. For rs2273697, the interaction coefficient was positive when combining GA+AA (β = 0.16, 95%CI 0.01, 0.32) versus GG. Conclusion The ABC transporters appear to play a role in accumulation of MeHg during early development.
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Affiliation(s)
- Sabrina Llop
- Foundation for the Promotion of Health and Biomedical Research in the Valencian Region, FISABIO, Valencia, Spain
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain
| | - Karin Engström
- Division of Occupational and Environmental Medicine, Lund University, Lund, Sweden
| | - Ferran Ballester
- Foundation for the Promotion of Health and Biomedical Research in the Valencian Region, FISABIO, Valencia, Spain
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain
- School of Nursing, University of Valencia, Valencia, Spain
| | - Elisa Franforte
- Division of Occupational and Environmental Medicine, Lund University, Lund, Sweden
| | - Ayman Alhamdow
- Division of Occupational and Environmental Medicine, Lund University, Lund, Sweden
| | - Federica Pisa
- Unit of Hygiene and Epidemiology, University of Udine, Udine, Italy
| | - Janja Snoj Tratnik
- Department of Environmental Sciences, Jožef Stefan Institute, Ljubljana, Slovenia
| | - Datja Mazej
- Department of Environmental Sciences, Jožef Stefan Institute, Ljubljana, Slovenia
| | - Mario Murcia
- Foundation for the Promotion of Health and Biomedical Research in the Valencian Region, FISABIO, Valencia, Spain
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain
| | - Marisa Rebagliato
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain
- Medicine Department, Jaume I University, Castelló de la Plana, Spain
| | - Mariona Bustamante
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain
- Centre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain
- Hospital del Mar Research Institute (IMIM), Barcelona, Spain
- Center for Genomic Regulation (CRG), Barcelona, Spain
| | - Jordi Sunyer
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Madrid, Spain
- Centre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain
- Hospital del Mar Research Institute (IMIM), Barcelona, Spain
- Pompeu Fabra University (UPF), Barcelona, Spain
| | | | - Alexia Prasouli
- Department of Social and Developmental Paediatrics Institute of Child Health, Athens, Greece
| | - Eleni Antonopoulou
- Department of Social and Developmental Paediatrics Institute of Child Health, Athens, Greece
| | - Ioanna Antoniadou
- Department of Social and Developmental Paediatrics Institute of Child Health, Athens, Greece
| | - Sheena Nakou
- Department of Social and Developmental Paediatrics Institute of Child Health, Athens, Greece
| | - Fabio Barbone
- Unit of Hygiene and Epidemiology, University of Udine, Udine, Italy
| | - Milena Horvat
- Department of Environmental Sciences, Jožef Stefan Institute, Ljubljana, Slovenia
| | - Karin Broberg
- Division of Occupational and Environmental Medicine, Lund University, Lund, Sweden
- Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden
- * E-mail:
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527
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Korte HL, Fels SR, Christensen GA, Price MN, Kuehl JV, Zane GM, Deutschbauer AM, Arkin AP, Wall JD. Genetic basis for nitrate resistance in Desulfovibrio strains. Front Microbiol 2014; 5:153. [PMID: 24795702 PMCID: PMC4001038 DOI: 10.3389/fmicb.2014.00153] [Citation(s) in RCA: 162] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Accepted: 03/21/2014] [Indexed: 12/31/2022] Open
Abstract
Nitrate is an inhibitor of sulfate-reducing bacteria (SRB). In petroleum production sites, amendments of nitrate and nitrite are used to prevent SRB production of sulfide that causes souring of oil wells. A better understanding of nitrate stress responses in the model SRB, Desulfovibrio vulgaris Hildenborough and Desulfovibrio alaskensis G20, will strengthen predictions of environmental outcomes of nitrate application. Nitrate inhibition of SRB has historically been considered to result from the generation of small amounts of nitrite, to which SRB are quite sensitive. Here we explored the possibility that nitrate might inhibit SRB by a mechanism other than through nitrite inhibition. We found that nitrate-stressed D. vulgaris cultures grown in lactate-sulfate conditions eventually grew in the presence of high concentrations of nitrate, and their resistance continued through several subcultures. Nitrate consumption was not detected over the course of the experiment, suggesting adaptation to nitrate. With high-throughput genetic approaches employing TnLE-seq for D. vulgaris and a pooled mutant library of D. alaskensis, we determined the fitness of many transposon mutants of both organisms in nitrate stress conditions. We found that several mutants, including homologs present in both strains, had a greatly increased ability to grow in the presence of nitrate but not nitrite. The mutated genes conferring nitrate resistance included the gene encoding the putative Rex transcriptional regulator (DVU0916/Dde_2702), as well as a cluster of genes (DVU0251-DVU0245/Dde_0597-Dde_0605) that is poorly annotated. Follow-up studies with individual D. vulgaris transposon and deletion mutants confirmed high-throughput results. We conclude that, in D. vulgaris and D. alaskensis, nitrate resistance in wild-type cultures is likely conferred by spontaneous mutations. Furthermore, the mechanisms that confer nitrate resistance may be different from those that confer nitrite resistance.
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Affiliation(s)
- Hannah L Korte
- Department of Biochemistry, University of Missouri Columbia, MO, USA ; Ecosystems and Networks Integrated with Genes and Molecular Assemblies Berkeley, CA, USA
| | - Samuel R Fels
- Ecosystems and Networks Integrated with Genes and Molecular Assemblies Berkeley, CA, USA ; Department of Molecular Microbiology and Immunology, University of Missouri Columbia, MO, USA
| | - Geoff A Christensen
- Department of Biochemistry, University of Missouri Columbia, MO, USA ; Ecosystems and Networks Integrated with Genes and Molecular Assemblies Berkeley, CA, USA
| | - Morgan N Price
- Ecosystems and Networks Integrated with Genes and Molecular Assemblies Berkeley, CA, USA ; Physical Biosciences Division, Lawrence Berkeley National Laboratory Berkeley, CA, USA
| | - Jennifer V Kuehl
- Ecosystems and Networks Integrated with Genes and Molecular Assemblies Berkeley, CA, USA ; Physical Biosciences Division, Lawrence Berkeley National Laboratory Berkeley, CA, USA
| | - Grant M Zane
- Department of Biochemistry, University of Missouri Columbia, MO, USA ; Ecosystems and Networks Integrated with Genes and Molecular Assemblies Berkeley, CA, USA
| | - Adam M Deutschbauer
- Ecosystems and Networks Integrated with Genes and Molecular Assemblies Berkeley, CA, USA ; Physical Biosciences Division, Lawrence Berkeley National Laboratory Berkeley, CA, USA
| | - Adam P Arkin
- Ecosystems and Networks Integrated with Genes and Molecular Assemblies Berkeley, CA, USA ; Physical Biosciences Division, Lawrence Berkeley National Laboratory Berkeley, CA, USA
| | - Judy D Wall
- Department of Biochemistry, University of Missouri Columbia, MO, USA ; Ecosystems and Networks Integrated with Genes and Molecular Assemblies Berkeley, CA, USA ; Department of Molecular Microbiology and Immunology, University of Missouri Columbia, MO, USA
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528
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USE OF CELLULOSE FILTER PAPER TO QUANTIFY WHOLE-BLOOD MERCURY IN TWO MARINE MAMMALS: VALIDATION STUDY. J Wildl Dis 2014; 50:271-8. [DOI: 10.7589/2013-08-214] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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529
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Chiasson-Gould SA, Blais JM, Poulain AJ. Dissolved organic matter kinetically controls mercury bioavailability to bacteria. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:3153-61. [PMID: 24524696 DOI: 10.1021/es4038484] [Citation(s) in RCA: 122] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Predicting the bioavailability of inorganic mercury (Hg) to bacteria that produce the potent bioaccumulative neurotoxin monomethylmercury remains one of the greatest challenges in predicting the environmental fate and transport of Hg. Dissolved organic matter (DOM) affects mercury methylation due to its influence on cell physiology (as a potential nutrient) and its influence on Hg(II) speciation in solution (as a complexing agent), therefore controlling Hg bioavailability. We assessed the role of DOM on Hg(II) bioavailability to a gram-negative bacterium bioreporter under oxic pseudo- and nonequilibrium conditions, using defined media and field samples spanning a wide range of DOM levels. Our results showed that Hg(II) was considerably more bioavailable under nonequilibrium conditions than when DOM was absent or when Hg(II) and DOM had reached pseudoequilibrium (24 h) prior to cell exposure. Under these enhanced uptake conditions, Hg(II) bioavailability followed a bell shaped curve as DOM concentrations increased, both for defined media and natural water samples, consistent with bioaccumulation results in a companion paper (this issue) observed for amphipods. Experiments also suggest that DOM may not only provide shuttle molecules facilitating Hg uptake, but also alter cell wall properties to facilitate the first steps toward Hg(II) internalization. We propose the existence of a short-lived yet critical time window (<24 h) during which DOM facilitates the entry of newly deposited Hg(II) into aquatic food webs, suggesting that the bulk of mercury incorporation in aquatic food webs would occur within hours following its deposition from the atmosphere.
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Affiliation(s)
- Sophie A Chiasson-Gould
- Department of Biology, University of Ottawa , 30 Marie-Curie, Ottawa, Ontario, K1N 6N5, Canada
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530
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Stoeva MK, Aris-Brosou S, Chételat J, Hintelmann H, Pelletier P, Poulain AJ. Microbial community structure in lake and wetland sediments from a high Arctic polar desert revealed by targeted transcriptomics. PLoS One 2014; 9:e89531. [PMID: 24594936 PMCID: PMC3940601 DOI: 10.1371/journal.pone.0089531] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Accepted: 01/22/2014] [Indexed: 11/18/2022] Open
Abstract
While microbial communities play a key role in the geochemical cycling of nutrients and contaminants in anaerobic freshwater sediments, their structure and activity in polar desert ecosystems are still poorly understood, both across heterogeneous freshwater environments such as lakes and wetlands, and across sediment depths. To address this question, we performed targeted environmental transcriptomics analyses and characterized microbial diversity across three depths from sediment cores collected in a lake and a wetland, located on Cornwallis Island, NU, Canada. Microbial communities were characterized based on 16S rRNA and two functional gene transcripts: mcrA, involved in archaeal methane cycling and glnA, a bacterial housekeeping gene implicated in nitrogen metabolism. We show that methane cycling and overall bacterial metabolic activity are the highest at the surface of lake sediments but deeper within wetland sediments. Bacterial communities are highly diverse and structured as a function of both environment and depth, being more diverse in the wetland and near the surface. Archaea are mostly methanogens, structured by environment and more diverse in the wetland. McrA transcript analyses show that active methane cycling in the lake and wetland corresponds to distinct communities with a higher potential for methane cycling in the wetland. Methanosarcina spp., Methanosaeta spp. and a group of uncultured Archaea are the dominant methanogens in the wetland while Methanoregula spp. predominate in the lake.
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Affiliation(s)
| | - Stéphane Aris-Brosou
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
- Department of Mathematics and Statistics, University of Ottawa, Ottawa, Ontario, Canada
| | - John Chételat
- Environment Canada, National Wildlife Research Centre, Ottawa, Ontario, Canada
| | - Holger Hintelmann
- Department of Chemistry, Trent University, Peterborough, Ontario, Canada
| | - Philip Pelletier
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
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531
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Analysis of the microbial community structure by monitoring an Hg methylation gene (hgcA) in paddy soils along an Hg gradient. Appl Environ Microbiol 2014; 80:2874-9. [PMID: 24584244 DOI: 10.1128/aem.04225-13] [Citation(s) in RCA: 92] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Knowledge of the diversity of mercury (Hg)-methylating microbes in the environment is limited due to a lack of available molecular biomarkers. Here, we developed novel degenerate PCR primers for a key Hg-methylating gene (hgcA) and amplified successfully the targeted genes from 48 paddy soil samples along an Hg concentration gradient in the Wanshan Hg mining area of China. A significant positive correlation was observed between hgcA gene abundance and methylmercury (MeHg) concentrations, suggesting that microbes containing the genes contribute to Hg methylation in the sampled soils. Canonical correspondence analysis (CCA) showed that the hgcA gene diversity in microbial community structures from paddy soils was high and was influenced by the contents of total Hg, SO4(2-), NH4(+), and organic matter. Phylogenetic analysis showed that hgcA microbes in the sampled soils likely were related to Deltaproteobacteria, Firmicutes, Chloroflexi, Euryarchaeota, and two unclassified groups. This is a novel report of hgcA diversity in paddy habitats, and results here suggest a link between Hg-methylating microbes and MeHg contamination in situ, which would be useful for monitoring and mediating MeHg synthesis in soils.
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532
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Thakur S, Kumari S, Dogra P, Chauhan GS. A new guar gum-based adsorbent for the removal of Hg(II) from its aqueous solutions. Carbohydr Polym 2014; 106:276-82. [PMID: 24721079 DOI: 10.1016/j.carbpol.2014.02.041] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Revised: 01/25/2014] [Accepted: 02/12/2014] [Indexed: 10/25/2022]
Abstract
Modification of biopolymers by oxidation is an easy process to develop effective adsorbents for the removal of toxic metal ions from their aqueous solutions. In the present study, guar gum (GG) was crosslinked with epichlorohydrin and then oxidized to the polydialdehyde form (GG-clPDA). The latter was converted to a Schiff-base, GG-clCHN(CH2)6NCHGG, by reaction with hexamethylenediamine. Different forms of the modified GG were characterized by SEM, FTIR and XRD and investigated as adsorbents for the removal of Hg(II) ions from their aqueous solutions. The adsorption process was carried out through the variation of time, temperature, pH and initial concentration of Hg(II) ions. GG-clCHN(CH2)6NCHGG was observed to be an efficient adsorbent with a maximum adsorption capacity of 41.13 mg/g. It is reusable up to five cycles at the optimum conditions obtained for the maximum ions uptake. The kinetic data generated fit the Freundlich isotherm and pseudo-second order kinetics.
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Affiliation(s)
- Shiwali Thakur
- Himachal Pradesh University, Department of Chemistry, Shimla 171005, India
| | - Sapana Kumari
- Himachal Pradesh University, Department of Chemistry, Shimla 171005, India
| | - Priyanka Dogra
- Himachal Pradesh University, Department of Chemistry, Shimla 171005, India
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533
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St Pierre KA, Chétélat J, Yumvihoze E, Poulain AJ. Temperature and the sulfur cycle control monomethylmercury cycling in high Arctic coastal marine sediments from Allen Bay, Nunavut, Canada. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:2680-2687. [PMID: 24555761 DOI: 10.1021/es405253g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Monomethylmercury (MMHg) is a neurotoxin of concern in the Canadian Arctic due to its tendency to bioaccumulate and the importance of fish and wildlife in the Inuit diet. In lakes and wetlands, microbial sediment communities are integral to the cycling of MMHg; however, the role of Arctic marine sediments is poorly understood. With projected warming, the effect of temperature on the production and degradation of MMHg in Arctic environments also remains unclear. We examined MMHg dynamics across a temperature gradient (4, 12, 24 °C) in marine sediments collected in Allen Bay, Nunavut. Slurries were spiked with stable mercury isotopes and amended with specific microbial stimulants and inhibitors, and subsampled over 12 days. Maximal methylation and demethylation potentials were low, ranging from below detection to 1.13 pmol g(-1) h(-1) and 0.02 pmol g(-1) h(-1), respectively, suggesting that sediments are likely not an important source of MMHg to overlying water. Our results suggest that warming may result in an increase in Hg methylation - controlled by temperature-dependent sulfate reduction, without a compensatory increase in demethylation. This study highlights the need for further research into the role of high Arctic marine sediments and climate on the Arctic marine MMHg budget.
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Affiliation(s)
- K A St Pierre
- Department of Biology, University of Ottawa , 30 Marie-Curie, Ottawa, Ontario, K1N 6N5, Canada
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534
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Bravo AG, Cosio C, Amouroux D, Zopfi J, Chevalley PA, Spangenberg JE, Ungureanu VG, Dominik J. Extremely elevated methyl mercury levels in water, sediment and organisms in a Romanian reservoir affected by release of mercury from a chlor-alkali plant. WATER RESEARCH 2014; 49:391-405. [PMID: 24216231 DOI: 10.1016/j.watres.2013.10.024] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 09/17/2013] [Accepted: 10/09/2013] [Indexed: 05/25/2023]
Abstract
We examined mercury (Hg) biogeochemistry and biomagnification in the Babeni Reservoir, a system strongly affected by the release of Hg from a chlor-alkali plant. Total mercury (THg) concentrations in river water reached 88 ng L(-1) but decreased rapidly in the reservoir (to 9 ng L(-1)). In contrast, monomethylmercury (MMHg) concentrations increased from the upstream part of the reservoir to the central part (0.7 ng L(-1)), suggesting high methylation within the reservoir. Moreover, vertical water column profiles of THg and MMHg indicated that Hg methylation mainly occurred deep in the water column and at the sediment-water interface. The discharge of Hg from a chlor-alkali plant in Valcea region caused the highest MMHg concentrations ever found in non-piscivorous fish worldwide. MMHg concentrations and bioconcentration factors (BCF) of plankton and macrophytes revealed that the highest biomagnification of MMHg takes place in primary producers.
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Affiliation(s)
- Andrea Garcia Bravo
- Institute F.-A. Forel, University of Geneva, 10, Route de Suisse, 1290 Versoix, Switzerland.
| | - Claudia Cosio
- Institute F.-A. Forel, University of Geneva, 10, Route de Suisse, 1290 Versoix, Switzerland
| | - David Amouroux
- Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, IPREM UMR 5254 CNRS - Université de Pau et des Pays de l'Adour, Hélioparc, 64053 Pau, France
| | - Jakob Zopfi
- Environmental Geosciences, University of Basel, Bernoullistrasse 30, 4056 Basel, Switzerland
| | | | - Jorge E Spangenberg
- Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland
| | | | - Janusz Dominik
- Institute F.-A. Forel, University of Geneva, 10, Route de Suisse, 1290 Versoix, Switzerland
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535
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Rao B, Simpson C, Lin H, Liang L, Gu B. Determination of thiol functional groups on bacteria and natural organic matter in environmental systems. Talanta 2014; 119:240-7. [DOI: 10.1016/j.talanta.2013.11.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Revised: 10/31/2013] [Accepted: 11/02/2013] [Indexed: 10/26/2022]
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536
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Schartup AT, Balcom PH, Mason RP. Sediment-porewater partitioning, total sulfur, and methylmercury production in estuaries. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:954-60. [PMID: 24344684 PMCID: PMC4074365 DOI: 10.1021/es403030d] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Mercury (Hg) speciation and the activity of Hg(II)-methylating bacteria are responsible for the rate of methylmercury production and thus bioaccumulation in marine foodwebs. Factors affecting porewater partitioning (Kd) and methylation of Hg(II) were examined at 11 sites in sediment of 4 biogeochemically diverse estuaries in the Northeast U.S. In Long Island Sound, 88% of total mercury (HgT) log Kd variability was described by porewater dissolved organic carbon concentration and sediment total sulfur (S) content. Whereas across all estuaries, regression analyses showed that S alone drives about 70% of Kd variability and 50% of changes in methylation rates; and the inclusion of DOC and sulfides did not improve the prediction. Thus, we demonstrated that S is a better predictor of HgT log Kd than the sediment organic matter across multiple estuaries, and while organic matter and S are interchangeable in small-scale studies, on a larger scale, sediment S content is the simplest and most effective variable to measure.
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Affiliation(s)
- Amina T. Schartup
- University of Connecticut, Department of Marine Sciences, Groton Connecticut 06340
- Corresponding author: Tel: +1 (860) 373-0389
| | - Prentiss H. Balcom
- University of Connecticut, Department of Marine Sciences, Groton Connecticut 06340
| | - Robert P. Mason
- University of Connecticut, Department of Marine Sciences, Groton Connecticut 06340
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537
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Wang X, Ye Z, Li B, Huang L, Meng M, Shi J, Jiang G. Growing rice aerobically markedly decreases mercury accumulation by reducing both Hg bioavailability and the production of MeHg. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:1878-1885. [PMID: 24383449 DOI: 10.1021/es4038929] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Rice consumption represents a major route of mercury (Hg) and methylmercury (MeHg) exposure for those living in certain areas of inland China. In this study we investigated the effects of water management on bioavailable Hg, MeHg, and sulfate-reducing bacteria (SRB, abundance and community composition) in rhizosphere soil, and total Hg (THg) and MeHg in rice plants grown under glasshouse and paddy field conditions. Aerobic conditions greatly decreased the amount of THg and MeHg taken up by rice plants and affected their distribution in different plant tissues. There were positive correlations between bioavailable Hg and THg in brown rice and roots and between numbers of SRB and MeHg in brown rice, roots, and rhizosphere soil. Furthermore, the community composition of SRB was dramatically influenced by the water management regimes. Our results demonstrate that the greatly reduced bioavailability of Hg and production of MeHg are due to decreased SRB numbers and proportion of Hg methylators in the rhizosphere under aerobic conditions. These are the main reasons for the reduced Hg and MeHg accumulation in aerobically grown rice. Water management is indicated as an effective measure that can be used to reduce Hg and MeHg uptake by rice plants from Hg-contaminated paddy fields.
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Affiliation(s)
- Xun Wang
- State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University , Guangzhou 510006, P. R. China
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538
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Schaefer JK, Szczuka A, Morel FMM. Effect of divalent metals on Hg(II) uptake and methylation by bacteria. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:3007-13. [PMID: 24512453 DOI: 10.1021/es405215v] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The production of methylmercury by some bacteria is a key first step in the accumulation and biomagnification of this toxic substance in aquatic food webs, a major human health concern. By direct measurement of cellular Hg(II) uptake in model iron and sulfate reducing bacteria, we have observed that specific trace metals, such as Zn(II) and Cd(II), inhibit uptake and methylation in these organisms, whereas other metals, such as Ni(II), Co(II), or Fe(II), do not. The inhibition of Hg(II) methylation by Zn(II) was competitive in nature and related to the concentration of inorganically complexed Zn(II) (Zn'). The inhibition of Hg(II) methylation was alleviated by decreasing the free Zn' concentration through complexation with nitrilotriacetic acid without altering the speciation of Hg(II). The inhibitory effect by Zn(II) was observed when either Hg-cysteine complexes or neutral HgCl2 dominated the speciation of Hg(II), demonstrating that both charged and neutral species are transported into the cytosol by an active rather than passive process. We propose that Hg(II) uptake is the result of its accidental uptake by metal transporter(s), possibly one effecting the transport of Zn(II).
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Affiliation(s)
- Jeffra K Schaefer
- Department of Geosciences, Princeton University , Princeton, New Jersey 08544, United States
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539
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Grégoire DS, Poulain AJ. A little bit of light goes a long way: the role of phototrophs on mercury cycling. Metallomics 2014; 6:396-407. [DOI: 10.1039/c3mt00312d] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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540
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Thomas SA, Tong T, Gaillard JF. Hg(ii) bacterial biouptake: the role of anthropogenic and biogenic ligands present in solution and spectroscopic evidence of ligand exchange reactions at the cell surface. Metallomics 2014; 6:2213-22. [DOI: 10.1039/c4mt00172a] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
XANES spectra reveal a ligand exchange reaction between an aqueous Hg(ii)–organic ligand complex and thiol moieties at theE. colimembrane.
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Affiliation(s)
- Sara Anne Thomas
- Department of Civil and Environmental Engineering
- Northwestern University
- Evanston, USA
| | - Tiezheng Tong
- Department of Civil and Environmental Engineering
- Northwestern University
- Evanston, USA
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541
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Liu YR, Zheng YM, Zhang LM, He JZ. Linkage between community diversity of sulfate-reducing microorganisms and methylmercury concentration in paddy soil. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2014; 21:1339-1348. [PMID: 23900947 DOI: 10.1007/s11356-013-1973-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2013] [Accepted: 07/01/2013] [Indexed: 06/02/2023]
Abstract
Sulfate-reducing microorganisms (SRM) have been thought to play a key role in mercury (Hg) methylation in anoxic environments. The current study examined the linkage between SRM abundance and diversity and contents of methylmercury (MeHg) in paddy soils collected from a historical Hg mining area in China. Soil profile samples were collected from four sites over a distance gradient downstream the Hg mining operation. Results showed that MeHg content in the soil of each site significantly decreased with the extending distance away from Hg mine. Soil MeHg content was correlated positively with abundance of SRM and the contents of organic matter (OM), NH4(+), SO4(2-), and Hg. The abundances of SRM based on dissimilatory (bi) sulfite reductase (dsrAB) gene at 0-40 cm depths were higher than those at 40-80 cm depth at all sites. The SRM community composition varied in the soils of different sampling sites following terminal restriction fragment length polymorphism (T-RFLP) and phylogenetic analyses, which appeared to be correlated with contents of MeHg, OM, NH4(+), and SO4(2-) through canonical correspondence analysis. The dominant groups of SRM in the soils examined belonged to Deltaproteobacteria and some unknown SRM clusters that could have potential for Hg methylation. These results advance our understanding of the relationship between SRM and methylmercury concentration in paddy soil.
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Affiliation(s)
- Yu-Rong Liu
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China
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542
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Zhou J, Riccardi D, Beste A, Smith JC, Parks JM. Mercury methylation by HgcA: theory supports carbanion transfer to Hg(II). Inorg Chem 2013; 53:772-7. [PMID: 24377658 DOI: 10.1021/ic401992y] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Many proteins use corrinoid cofactors to facilitate methyl transfer reactions. Recently, a corrinoid protein, HgcA, has been shown to be required for the production of the neurotoxin methylmercury by anaerobic bacteria. A strictly conserved Cys residue in HgcA was predicted to be a lower-axial ligand to Co(III), which has never been observed in a corrinoid protein. Here, we use density functional theory to study homolytic and heterolytic Co-C bond dissociation and methyl transfer to Hg(II) substrates with model methylcobalamin complexes containing a lower-axial Cys or His ligand to cobalt, the latter of which is commonly found in other corrinoid proteins. We find that Cys thiolate coordination to Co facilitates both methyl radical and methyl carbanion transfer to Hg(II) substrates, but carbanion transfer is more favorable overall in the condensed phase. Thus, our findings are consistent with HgcA representing a new class of corrinoid protein capable of transferring methyl groups to electrophilic substrates.
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Affiliation(s)
- Jing Zhou
- Graduate School of Genome Science and Technology, University of Tennessee , Knoxville, Tennessee 37996, United States
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543
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Kumar N, Kozlowski PM. Mechanistic Insights for Formation of an Organometallic Co–C Bond in the Methyl Transfer Reaction Catalyzed by Methionine Synthase. J Phys Chem B 2013; 117:16044-57. [DOI: 10.1021/jp4093145] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Neeraj Kumar
- Department of Chemistry, University of Louisville, 2320
South Brook Street, Louisville, Kentucky 40292, United States
| | - Pawel M. Kozlowski
- Department of Chemistry, University of Louisville, 2320
South Brook Street, Louisville, Kentucky 40292, United States
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544
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Quiñones MA, Ruiz-Díez B, Fajardo S, López-Berdonces MA, Higueras PL, Fernández-Pascual M. Lupinus albus plants acquire mercury tolerance when inoculated with an Hg-resistant Bradyrhizobium strain. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2013; 73:168-175. [PMID: 24125840 DOI: 10.1016/j.plaphy.2013.09.015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Accepted: 09/20/2013] [Indexed: 05/29/2023]
Abstract
One strain of Bradyrhizobium canariense (L-7AH) was selected for its metal-resistance and ability to nodulate white lupin (Lupinus albus L.) plants, from a collection of rhizobial strains previously created from soils of the Almadén mining district (Spain) with varying levels of Hg contamination. Plants were inoculated with either strain L-7AH (Hg-tolerant) or L-3 (Hg-sensitive, used as control), and watered with nutrient solutions supplemented with various concentrations (0-200 μM) of HgCl2 in a growth chamber. L. albus inoculated with L-7AH were able to nodulate even at the highest concentration of Hg while those inoculated with L-3 had virtually no nodules at Hg concentrations above 25 μM. Plants inoculated with L-7AH, but not those with the control strain, were able to accumulate large amounts of Hg in their roots and nodules. Nodulation with L-7AH allowed plants to maintain constant levels of both chlorophylls and carotenoids in their leaves and a high photosynthetic efficiency, whereas in those inoculated with L-3 both pigment content and photosynthetic efficiency decreased significantly as Hg concentration increased. Nitrogenase activity of plants nodulated with L-7AH remained fairly constant at all concentrations of Hg used. Results suggest that this symbiotic pair may be used for rhizoremediation of Hg-contaminated soils.
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Affiliation(s)
- Miguel A Quiñones
- Instituto de Ciencias Agrarias (ICA), CSIC, Serrano 115-bis, 28006 Madrid, Spain.
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545
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546
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Gilmour CC, Podar M, Bullock AL, Graham AM, Brown SD, Somenahally AC, Johs A, Hurt RA, Bailey KL, Elias DA. Mercury methylation by novel microorganisms from new environments. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:11810-20. [PMID: 24024607 DOI: 10.1021/es403075t] [Citation(s) in RCA: 409] [Impact Index Per Article: 37.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Microbial mercury (Hg) methylation transforms a toxic trace metal into the highly bioaccumulated neurotoxin methylmercury (MeHg). The lack of a genetic marker for microbial MeHg production has prevented a clear understanding of Hg-methylating organism distribution in nature. Recently, a specific gene cluster (hgcAB) was linked to Hg methylation in two bacteria.1 Here we test if the presence of hgcAB orthologues is a reliable predictor of Hg methylation capability in microorganisms, a necessary confirmation for the development of molecular probes for Hg-methylation in nature. Although hgcAB orthologues are rare among all available microbial genomes, organisms are much more phylogenetically and environmentally diverse than previously thought. By directly measuring MeHg production in several bacterial and archaeal strains encoding hgcAB, we confirmed that possessing hgcAB predicts Hg methylation capability. For the first time, we demonstrated Hg methylation in a number of species other than sulfate- (SRB) and iron- (FeRB) reducing bacteria, including methanogens, and syntrophic, acetogenic, and fermentative Firmicutes. Several of these species occupy novel environmental niches for Hg methylation, including methanogenic habitats such as rice paddies, the animal gut, and extremes of pH and salinity. Identification of these organisms as Hg methylators now links methylation to discrete gene markers in microbial communities.
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Affiliation(s)
- Cynthia C Gilmour
- Smithsonian Environmental Research Center , Edgewater, Maryland, United States
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547
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Wiener JG. Mercury exposed: advances in environmental analysis and ecotoxicology of a highly toxic metal. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2013; 32:2175-2178. [PMID: 24006332 DOI: 10.1002/etc.2333] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2013] [Revised: 06/26/2013] [Accepted: 07/22/2013] [Indexed: 06/02/2023]
Affiliation(s)
- James G Wiener
- River Studies Center, University of Wisconsin-La Crosse, La Crosse, Wisconsin, USA.
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548
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Hu H, Lin H, Zheng W, Rao B, Feng X, Liang L, Elias DA, Gu B. Mercury reduction and cell-surface adsorption by Geobacter sulfurreducens PCA. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2013; 47:10922-30. [PMID: 24020841 DOI: 10.1021/es400527m] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Both reduction and surface adsorption of mercuric mercury [Hg(II)] are found to occur simultaneously on G. sulfurreducens PCA cells under dark, anaerobic conditions. Reduction of Hg(II) to elemental Hg(0) initially follows a pseudo-first order kinetics with a half-life of <2 h in the presence of 50 nM Hg(II) and 10(11) cells L(-1) in a phosphate buffer (pH 7.4). Multiple gene deletions of the outer membrane cytochromes in this organism resulted in a decrease in reduction rate from ∼0.3 to 0.05 h(-1), and reduction was nearly absent with heat-killed cells or in the cell filtrate. Adsorption of Hg(II) by cells is found to compete with, and thus inhibit, Hg(II) reduction. Depending on the Hg to cell ratio, maximum Hg(II) reduction was observed at about 5 × 10(-19) mol Hg cell(-1), but reduction terminated at a low Hg to cell ratio (<10(-20) mol Hg cell(-1)). This inhibitory effect is attributed to bonding between Hg(II) and the thiol (-SH) functional groups on cells and validated by experiments in which the sorbed Hg(II) was readily exchanged by thiols (e.g., glutathione) but not by carboxylate compounds such as ethylenediamine-tetraacetate (EDTA). We suggest that coupled Hg(II)-cell interactions, i.e., reduction and surface binding, could be important in controlling Hg species transformation and bioavailability and should therefore be considered in microbial Hg(II) uptake and methylation studies.
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Affiliation(s)
- Haiyan Hu
- State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences , Guangzhou, Guangdong, 510640, China
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549
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550
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Draft genome sequences for three mercury-methylating, sulfate-reducing bacteria. GENOME ANNOUNCEMENTS 2013; 1:1/4/e00618-13. [PMID: 23950126 PMCID: PMC3744682 DOI: 10.1128/genomea.00618-13] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The genetic basis for bacterial mercury methylation has been described recently. For insights into the physiology of mercury-methylating bacteria, we present genome sequences for Desulfococcus multivorans strain DSM 2059, Desulfovibrio alkalitolerans strain DSM 16529, and Desulfovibrio species strain X2.
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