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Celo V, Lean DRS, Scott SL. Abiotic methylation of mercury in the aquatic environment. THE SCIENCE OF THE TOTAL ENVIRONMENT 2006; 368:126-37. [PMID: 16226793 DOI: 10.1016/j.scitotenv.2005.09.043] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2004] [Revised: 06/20/2005] [Accepted: 09/12/2005] [Indexed: 05/04/2023]
Abstract
Methylation of inorganic mercury in the aquatic environment has been considered to be largely the result of biological processes, primarily involving sulfate-reducing bacteria. However, these processes cannot account for all of the methylmercury that is formed naturally. A growing body of evidence suggests that chemical reactions represent another possible pathway for mercury methylation in the aquatic environment. In order to assess the abiotic contribution to mercury methylation in the water column, and specifically the conditions under which this contribution may be significant, the current state of knowledge about environmentally significant methylation reactions is reviewed. Results of our laboratory-based investigations of aqueous mercury reactions with some potential methyl donors, including MeCo(dmg)(2)(H2O), a simple model for methylcobalamin, various methyltin compounds and methyl iodide, are presented. In each reaction, the yield of methylmercury and the rate of methylation depend strongly on environmental factors such as pH, temperature, and the presence of complexing agents, especially chloride.
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Affiliation(s)
- Valbona Celo
- Department of Chemistry, University of Ottawa, Ottawa, ON, Canada.
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52
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Holmes J, Lean D. Factors that influence methylmercury flux rates from wetland sediments. THE SCIENCE OF THE TOTAL ENVIRONMENT 2006; 368:306-19. [PMID: 16410019 DOI: 10.1016/j.scitotenv.2005.11.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2004] [Revised: 11/11/2005] [Accepted: 11/29/2005] [Indexed: 05/06/2023]
Abstract
Sediments are thought to be an important source of methylmercury (MeHg) to the water column of wetlands. We measured sediment MeHg pore water concentrations as a function of depth in four wetlands to determine the concentration gradient and used it determine sediment-water flux of MeHg. Fluxes of MeHg ranged from -1.60 to 10.02 ng m(-2) day(-1) and were shown to be a function of 1) redox conditions at the sediment-water interface, 2) oxygen gradient above the sediment surface, 3) water temperature, and 4) pore water and water column-dissolved sulphide. MeHg water column concentration in each of the four wetlands was positively correlated with MeHg concentrations present in surface sediment and pore water, and with the calculated sediment-water MeHg flux rate. In addition to MeHg, ethylmercury (EtHg) was detected in the sediment in all four wetlands, but not in the pore water or the water column. EtHg levels in sediment exceeded MeHg concentrations in two of the wetlands. This demonstrates that Hg ethylation is a significant part of the Hg cycle in some aquatic environments.
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Affiliation(s)
- Jonathan Holmes
- Biology Department, University of Ottawa, Ottawa, ON, Canada.
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53
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Fleming EJ, Mack EE, Green PG, Nelson DC. Mercury methylation from unexpected sources: molybdate-inhibited freshwater sediments and an iron-reducing bacterium. Appl Environ Microbiol 2006; 72:457-64. [PMID: 16391078 PMCID: PMC1352261 DOI: 10.1128/aem.72.1.457-464.2006] [Citation(s) in RCA: 327] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Methylmercury has been thought to be produced predominantly by sulfate-reducing bacteria in anoxic sediments. Here we show that in circumneutral pH sediments (Clear Lake, CA) application of a specific inhibitor of sulfate-reducing bacteria at appropriate concentrations typically inhibited less than one-half of all anaerobic methylation of added divalent mercury. This suggests that one or more additional groups of microbes are active methylators in these sediments impacted by a nearby abandoned mercury mine. From Clear Lake sediments, we isolated the iron-reducing bacterium Geobacter sp. strain CLFeRB, which can methylate mercury at a rate comparable to Desulfobulbus propionicus strain 1pr3, a sulfate-reducing bacterium known to be an active methylator. This is the first time that an iron-reducing bacterium has been shown to methylate mercury at environmentally significant rates. We suggest that mercury methylation by iron-reducing bacteria represents a previously unidentified and potentially significant source of this environmental toxin in iron-rich freshwater sediments.
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Affiliation(s)
- Emily J Fleming
- Section of Microbiology, 357 Briggs Hall, University of California, Davis, CA 95616, USA
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54
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Desrosiers M, Planas D, Mucci A. Mercury methylation in the epilithon of boreal shield aquatic ecosystems. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2006; 40:1540-6. [PMID: 16568768 DOI: 10.1021/es0508828] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Methylation rates by periphyton growing on the rocky shore of a remote boreal shield lake were measured over diurnal cycles at temperatures representative of summer and fall conditions. The measurements were carried out in vitro with natural communities grown on artificial Teflon substrates submerged along the lake's shore for 1-2 years. At temperatures above 20 degrees C, epilithon Hg methylation rates were fast and reached a steady state within 12 h upon exposure to 2 ng L(-1) of inorganic mercury. A variety of inhibitors were used to identify which microorganisms in the epilithic biofilm are responsible for the methylation. The addition of molybdate, which is believed to suppress the activity of sulfate-reducing bacteria, decreased methylmercury production rates by 60% in both light and dark experiments. The prokaryote inhibitor chloramphenicol reduced the methylation rate by 40% only during dark periods whereas an algal inhibitor (DCMU), which suppresses photosynthesis, decreased the methylation rate by 60% during light periods. Results of this study reveal that epilithon communities may be a significant source of MeHg to higher aquatic organisms in lakes and that the integrity of the epilithic biofilm is important for its ability to methylate Hg.
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Affiliation(s)
- Mélanie Desrosiers
- GEOTOP/UQAM/McGill Université du Québec a Montréal, C. P. 8888, Succursale Centre Ville, Montréal, Québec, Canada H3C 3P8
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55
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Fleming EJ, Mack EE, Green PG, Nelson DC. Mercury methylation from unexpected sources: molybdate-inhibited freshwater sediments and an iron-reducing bacterium. Appl Environ Microbiol 2006. [PMID: 16391078 DOI: 10.1128/aem.72.1.457] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2023] Open
Abstract
Methylmercury has been thought to be produced predominantly by sulfate-reducing bacteria in anoxic sediments. Here we show that in circumneutral pH sediments (Clear Lake, CA) application of a specific inhibitor of sulfate-reducing bacteria at appropriate concentrations typically inhibited less than one-half of all anaerobic methylation of added divalent mercury. This suggests that one or more additional groups of microbes are active methylators in these sediments impacted by a nearby abandoned mercury mine. From Clear Lake sediments, we isolated the iron-reducing bacterium Geobacter sp. strain CLFeRB, which can methylate mercury at a rate comparable to Desulfobulbus propionicus strain 1pr3, a sulfate-reducing bacterium known to be an active methylator. This is the first time that an iron-reducing bacterium has been shown to methylate mercury at environmentally significant rates. We suggest that mercury methylation by iron-reducing bacteria represents a previously unidentified and potentially significant source of this environmental toxin in iron-rich freshwater sediments.
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Affiliation(s)
- Emily J Fleming
- Section of Microbiology, 357 Briggs Hall, University of California, Davis, CA 95616, USA
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56
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Barkay T, Wagner-Döbler I. Microbial Transformations of Mercury: Potentials, Challenges, and Achievements in Controlling Mercury Toxicity in the Environment. ADVANCES IN APPLIED MICROBIOLOGY 2005; 57:1-52. [PMID: 16002008 DOI: 10.1016/s0065-2164(05)57001-1] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Tamar Barkay
- Department of Biochemistry and Microbiology, Cook College, Rutgers University, New Brunswick, New Jersey 08901, USA.
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57
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Schelert J, Dixit V, Hoang V, Simbahan J, Drozda M, Blum P. Occurrence and characterization of mercury resistance in the hyperthermophilic archaeon Sulfolobus solfataricus by use of gene disruption. J Bacteriol 2004; 186:427-37. [PMID: 14702312 PMCID: PMC305765 DOI: 10.1128/jb.186.2.427-437.2004] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mercury resistance mediated by mercuric reductase (MerA) is widespread among bacteria and operates under the control of MerR. MerR represents a unique class of transcription factors that exert both positive and negative regulation on gene expression. Archaea and bacteria are prokaryotes, yet little is known about the biological role of mercury in archaea or whether a resistance mechanism occurs in these organisms. The archaeon Sulfolobus solfataricus was sensitive to mercuric chloride, and low-level adaptive resistance could be induced by metal preconditioning. Protein phylogenetic analysis of open reading frames SSO2689 and SSO2688 clarified their identity as orthologs of MerA and MerR. Northern analysis established that merA transcription responded to mercury challenge, since mRNA levels were transiently induced and, when normalized to 7S RNA, approximated values for other highly expressed transcripts. Primer extension analysis of merA mRNA predicted a noncanonical TATA box with nonstandard transcription start site spacing. The functional roles of merA and merR were clarified further by gene disruption. The merA mutant exhibited mercury sensitivity relative to wild type and was defective in elemental mercury volatilization, while the merR mutant was mercury resistant. Northern analysis of the merR mutant revealed merA transcription was constitutive and that transcript abundance was at maximum levels. These findings constitute the first report of an archaeal heavy metal resistance system; however, unlike bacteria the level of resistance is much lower. The archaeal system employs a divergent MerR protein that acts only as a negative transcriptional regulator of merA expression.
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Affiliation(s)
- James Schelert
- Beadle Center for Genetics, University of Nebraska, Lincoln, Nebraska 68588-0666, USA
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58
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59
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Warner KA, Roden EE, Bonzongo JC. Microbial mercury transformation in anoxic freshwater sediments under iron-reducing and other electron-accepting conditions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2003; 37:2159-65. [PMID: 12785521 DOI: 10.1021/es0262939] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Potential rates of microbial methylation of inorganic mercury (added as HgCl2) and degradation of methyl mercury (MeHg) (added as CH3HgCl) were investigated in anoxic sediments from the Mobile Alabama River Basin (MARB) dominated by different terminal electron-accepting processes (TEAPs). Potential rates of methylation were comparable under methanogenic and sulfate-reducing conditions but suppressed under iron-reducing conditions, in slurries of freshwater wetland sediment In contrast, MeHg degradation rates were similar under all three TEAPs. Microbial Hg methylation and MeHg degradation were also investigated in surface sediment from three riverine sites, two of which had iron reduction and one sulfate reduction, as the dominant TEAP (as determined by 14C-acetate metabolism and other biogeochemical measurements). Methylation was active in sulfate-reducing sediments of a tributary creek and suppressed in iron-reducing, sandy sediments from the open river, whereas MeHg degradation was active at all three sites. Although iron-reducing conditions often suppressed methylation, some methylation activity was observed in two out of three replicates from iron-reducing sediments collected near a dam. Given that MeHg degradation was consistently observed under all TEAPs, our results suggest that the net flux of MeHg from iron-reducing surface sediments may be suppressed (due to inhibition of gross MeHg production) compared to sediments supporting other TEAPs.
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Affiliation(s)
- Kimberly A Warner
- Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama 35487-0206, USA
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60
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Von Canstein H, Kelly S, Li Y, Wagner-Döbler I. Species diversity improves the efficiency of mercury-reducing biofilms under changing environmental conditions. Appl Environ Microbiol 2002; 68:2829-37. [PMID: 12039739 PMCID: PMC123942 DOI: 10.1128/aem.68.6.2829-2837.2002] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2001] [Accepted: 02/28/2002] [Indexed: 11/20/2022] Open
Abstract
Six mercury-resistant environmental proteobacterial isolates and one genetically modified mercury-resistant Pseudomonas putida strain were analyzed for physiological traits of adaptive relevance in an environment of packed-bed bioreactors designed for the decontamination of mercury-polluted chlor-alkali wastewater. The strains displayed characteristic differences in each trait (i.e., biofilm formation capability, growth rate in mercury contaminated wastewaters, and mercury reduction efficiency). Subsequently, they were immobilized either as a monoculture or as a mixed culture on porous carrier material in packed-bed bioreactors through which different batches of filter-sterilized industrial chlor-alkali wastewater were pumped. In monospecies bioreactors, the mercury retention efficiency was sensitive to rapidly increasing mercury concentrations in the wastewater. Mixed culture biofilms displayed a high mercury retention efficiency that was not affected by rapid increases in mercury or continuously high mercury concentrations. The dynamic in the community composition of the mixed culture bioreactors was determined by ribosomal intergenic spacer polymorphism analysis. Mercury-mediated selective pressure decreased the number of prevalent strains. Microbial diversity was completely restored after easing of the selective pressure. Microbial diversity provides a reservoir of strains with complementary ecological niches that results in a superior bioreactor performance under changing environmental conditions.
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Affiliation(s)
- Harald Von Canstein
- Division of Microbiology. Division of Biochemical Engineering, German Research Centre for Biotechnology, D-38124 Braunschweig, Germany.
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61
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Warner KA, Gilmour CC, Capone DG. Reductive dechlorination of 2,4-dichlorophenol and related microbial processes under limiting and non-limiting sulfate concentration in anaerobic mid-Chesapeake Bay sediments. FEMS Microbiol Ecol 2002; 40:159-65. [DOI: 10.1111/j.1574-6941.2002.tb00948.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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62
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von Canstein H, Li Y, Leonhäuser J, Haase E, Felske A, Deckwer WD, Wagner-Döbler I. Spatially oscillating activity and microbial succession of mercury-reducing biofilms in a technical-scale bioremediation system. Appl Environ Microbiol 2002; 68:1938-46. [PMID: 11916716 PMCID: PMC123881 DOI: 10.1128/aem.68.4.1938-1946.2002] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2001] [Accepted: 01/22/2002] [Indexed: 11/20/2022] Open
Abstract
Mercury-contaminated chemical wastewater of a mercury cell chloralkali plant was cleaned on site by a technical-scale bioremediation system. Microbial mercury reduction of soluble Hg(II) to precipitating Hg(0) decreased the mercury load of the wastewater during its flow through the bioremediation system by up to 99%. The system consisted of a packed-bed bioreactor, where most of the wastewater's mercury load was retained, and an activated carbon filter, where residual mercury was removed from the bioreactor effluent by both physical adsorption and biological reduction. In response to the oscillation of the mercury concentration in the bioreactor inflow, the zone of maximum mercury reduction oscillated regularly between the lower and the upper bioreactor horizons or the carbon filter. At low mercury concentrations, maximum mercury reduction occurred near the inflow at the bottom of the bioreactor. At high concentrations, the zone of maximum activity moved to the upper horizons. The composition of the bioreactor and carbon filter biofilms was investigated by 16S-23S ribosomal DNA intergenic spacer polymorphism analysis. Analysis of spatial biofilm variation showed an increasing microbial diversity along a gradient of decreasing mercury concentrations. Temporal analysis of the bioreactor community revealed a stable abundance of two prevalent strains and a succession of several invading mercury-resistant strains which was driven by the selection pressure of high mercury concentrations. In the activated carbon filter, a lower selection pressure permitted a steady increase in diversity during 240 days of operation and the establishment of one mercury-sensitive invader.
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MESH Headings
- Bacteria/classification
- Bacteria/genetics
- Bacteria/growth & development
- Bacteria/metabolism
- Biofilms/growth & development
- Bioreactors
- Chlorides
- DNA, Ribosomal Spacer/analysis
- Mercury/metabolism
- Microscopy, Electron, Scanning
- Oxidation-Reduction
- Oxygen Consumption
- RNA, Ribosomal, 16S/genetics
- RNA, Ribosomal, 23S/genetics
- Waste Disposal, Fluid/instrumentation
- Waste Disposal, Fluid/methods
- Water Microbiology
- Water Pollution, Chemical
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Affiliation(s)
- Harald von Canstein
- Division of Microbiology, German Research Centre for Biotechnology, 38124 Braunschweig, Germany.
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63
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King JK, Harmon SM, Fu TT, Gladden JB. Mercury removal, methylmercury formation, and sulfate-reducing bacteria profiles in wetland mesocosms. CHEMOSPHERE 2002; 46:859-870. [PMID: 11922066 DOI: 10.1016/s0045-6535(01)00135-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
A pilot-scale model was constructed to determine if a wetland treatment system (WTS) could effectively remove low-level mercury from an outfall located at the Department of Energy's Savannah River Site. Site-specific hydrosoil was planted with giant bulrush, Scirpus californicus, and surface amended with gypsum (CaSO4) prior to investigating the biogeochemical dynamics of sediment-based sulfur and mercury speciation. On average, the pilot WTS decreased total mercury concentrations in the outfall stream by 50%. Transformation of mercury to a more "bioavailable" species, methylmercury, was also observed in the wetland treatment system. Methylmercury formation in the wetland was ascertained with respect to sediment biogeochemistry and S. californicus influences. Differences in sulfate-reduction rates (SRRs) were observed between mesocosms that received additional decomposing Scirpus matter and mesocosms that were permitted growth of the submerged macrophyte, Potamogeton pusillus. Relative abundance measurements of sulfate-reducing bacteria (SRB) as characterized using oligonucleotide probes were also noticeably different between the two mesocosms. A positive correlation between increased sulfide, dissolved total mercury, and dissolved methylmercury concentrations was also observed in porewater. The data suggest that soluble mercury-sulfide complexes were formed and contributed, in part, to a slight increase in mercury solubility. Observed increases in methylmercury concentration also suggest that soluble mercury-sulfide complexes represent a significant source of mercury that is "available" for methylation. Finally, a volunteer macrophyte, Potamogeton pusillus, is implicated as having contributed additional suspended particulate matter in surface water that subsequently reduced the pool of dissolved mercury while also providing an environment suitable for demethylation.
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Affiliation(s)
- Jeffrey K King
- Westinghouse Savannah River Company, Aiken, SC 29808, USA.
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64
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King JK, Kostka JE, Frischer ME, Saunders FM, Jahnke RA. A quantitative relationship that demonstrates mercury methylation rates in marine sediments are based on the community composition and activity of sulfate-reducing bacteria. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2001; 35:2491-6. [PMID: 11432553 DOI: 10.1021/es001813q] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
A quantitative framework was developed which estimates mercury methylation rates (MMR) in sediment cores based on measured sulfate reduction rates (SRR) and the community composition sulfate-reducing bacterial consortia. MMR and SRR as well as group-specific 16S rRNA concentrations (as quantified by probe signal) associated with sulfate-reducing bacteria (SRB) were measured in triplicate cores of saltmarsh sediments. Utilizing previously documented conversion factors in conjunction with field observations of sulfate reduction, MMR were calculated, and the results were compared to experimentally derived measurements of MMR. Using our novel field data collected in saltmarsh sediment where sulfate reduction activity is high, calculated and independently measured MMR results were consistently within an order of magnitude and displayed similar trends with sediment depth. In an estuarine sediment where sulfate reduction activity was low, calculated and observed MMR diverged by greater than an order of magnitude, but again trends with depth were similar. We have expanded the small database generated to date on mercury methylation in sulfur-rich marine sediments. The quantitative frameworkwe have developed further elucidates the coupling of mercury methylation to sulfate reduction by basing calculated rates of mercury methylation on the activity and community composition of sulfate-reducing bacteria. The quantitative framework may also provide a promising alternative to the difficult and hazardous determination of MMR using radiolabeled mercury.
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Affiliation(s)
- J K King
- Skidaway Institute of Oceanography, Savannah, Georgia 31411, USA.
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65
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Benoit JM, Gilmour CC, Mason RP. Aspects of bioavailability of mercury for methylation in pure cultures of Desulfobulbus propionicus (1pr3). Appl Environ Microbiol 2001; 67:51-8. [PMID: 11133427 PMCID: PMC92513 DOI: 10.1128/aem.67.1.51-58.2001] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have previously hypothesized that sulfide inhibits Hg methylation by decreasing its bioavailability to sulfate-reducing bacteria (SRB), the important methylators of Hg in natural sediments. With a view to designing a bioassay to test this hypothesis, we investigated a number of aspects of Hg methylation by the SRB Desulfobulbus propionicus, including (i) the relationship between cell density and methylmercury (MeHg) production, (ii) the time course of Hg methylation relative to growth stage, (iii) changes in the bioavailability of an added inorganic Hg (Hg(I)) spike over time, and (iv) the dependence of methylation on the concentration of dissolved Hg(I) present in the culture. We then tested the effect of sulfide on MeHg production by this microorganism. These experiments demonstrated that under conditions of equal bioavailability, per-cell MeHg production was constant through log-phase culture growth. However, the methylation rate of a new Hg spike dramatically decreased after the first 5 h. This result was seen whether methylation rate was expressed as a fraction of the total added Hg or the filtered Hg(I) concentration, which suggests that Hg bioavailability decreased through both changes in Hg complexation and formation of solid phases. At low sulfide concentration, MeHg production was linearly related to the concentration of filtered Hg(I). The methylation of filtered Hg(I) decreased about fourfold as sulfide concentration was increased from 10(-6) to 10(-3) M. This decline is consistent with a decrease in the bioavailability of Hg(I), possibly due to a decline in the dissolved neutral complex, HgS(0).
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Affiliation(s)
- J M Benoit
- Estuarine Research Center, Academy of Natural Sciences, St. Leonard, Maryland 20685, USA.
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66
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González JM, Robb FT. Genetic analysis of Carboxydothermus hydrogenoformans carbon monoxide dehydrogenase genes cooF and cooS. FEMS Microbiol Lett 2000; 191:243-7. [PMID: 11024270 DOI: 10.1111/j.1574-6968.2000.tb09346.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Carboxydothermus hydrogenoformans is an extremely thermophilic, Gram-positive bacterium growing on carbon monoxide (CO) as single carbon and energy source and producing only H(2) and CO(2). Carbon monoxide dehydrogenase is a key enzyme for CO metabolism. The carbon monoxide dehydrogenase genes cooF and cooS from C. hydrogenoformans were cloned and sequenced. These genes showed the highest similarity to the cooF genes from the archaeon Archaeoglobus fulgidus and the cooS gene from the bacterium Rhodospirillum rubrum, respectively. The cooS gene was identified immediately downstream of cooF, however, the cooF and cooS genes from C. hydrogenoformans have substantially different codon usage, and the cooF gene Arg codon usage pattern, dominated by AGA and AGG, resembles the archaeal pattern. The data therefore suggest lateral transfer of these genes, possibly from different donor species.
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Affiliation(s)
- J M González
- Center of Marine Biotechnology, University of Maryland Biotechnology Institute, 701 E. Pratt St., Baltimore, MD, 21202, USA
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67
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King JK, Kostka JE, Frischer ME, Saunders FM. Sulfate-reducing bacteria methylate mercury at variable rates in pure culture and in marine sediments. Appl Environ Microbiol 2000; 66:2430-7. [PMID: 10831421 PMCID: PMC110551 DOI: 10.1128/aem.66.6.2430-2437.2000] [Citation(s) in RCA: 187] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Differences in methylmercury (CH(3)Hg) production normalized to the sulfate reduction rate (SRR) in various species of sulfate-reducing bacteria (SRB) were quantified in pure cultures and in marine sediment slurries in order to determine if SRB strains which differ phylogenetically methylate mercury (Hg) at similar rates. Cultures representing five genera of the SRB (Desulfovibrio desulfuricans, Desulfobulbus propionicus, Desulfococcus multivorans, Desulfobacter sp. strain BG-8, and Desulfobacterium sp. strain BG-33) were grown in a strictly anoxic, minimal medium that received a dose of inorganic Hg 120 h after inoculation. The mercury methylation rates (MMR) normalized per cell were up to 3 orders of magnitude higher in pure cultures of members of SRB groups capable of acetate utilization (e.g., the family Desulfobacteriaceae) than in pure cultures of members of groups that are not able to use acetate (e.g., the family Desulfovibrionaceae). Little or no Hg methylation was observed in cultures of Desulfobacterium or Desulfovibrio strains in the absence of sulfate, indicating that Hg methylation was coupled to respiration in these strains. Mercury methylation, sulfate reduction, and the identities of sulfate-reducing bacteria in marine sediment slurries were also studied. Sulfate-reducing consortia were identified by using group-specific oligonucleotide probes that targeted the 16S rRNA molecule. Acetate-amended slurries, which were dominated by members of the Desulfobacterium and Desulfobacter groups, exhibited a pronounced ability to methylate Hg when the MMR were normalized to the SRR, while lactate-amended and control slurries had normalized MMR that were not statistically different. Collectively, the results of pure-culture and amended-sediment experiments suggest that members of the family Desulfobacteriaceae have a greater potential to methylate Hg than members of the family Desulfovibrionaceae have when the MMR are normalized to the SRR. Hg methylation potential may be related to genetic composition and/or carbon metabolism in the SRB. Furthermore, we found that in marine sediments that are rich in organic matter and dissolved sulfide rapid CH(3)Hg accumulation is coupled to rapid sulfate reduction. The observations described above have broad implications for understanding the control of CH(3)Hg formation and for developing remediation strategies for Hg-contaminated sediments.
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Affiliation(s)
- J K King
- Skidaway Institute of Oceanography, Savannah, Georgia 31411, USA
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68
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King JK, Kostka JE, Frischer ME, Saunders FM. Sulfate-reducing bacteria methylate mercury at variable rates in pure culture and in marine sediments. Appl Environ Microbiol 2000. [PMID: 10831421 DOI: 10.1128/aem.66.6.2430-2437.2000.updated] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/03/2023] Open
Abstract
Differences in methylmercury (CH(3)Hg) production normalized to the sulfate reduction rate (SRR) in various species of sulfate-reducing bacteria (SRB) were quantified in pure cultures and in marine sediment slurries in order to determine if SRB strains which differ phylogenetically methylate mercury (Hg) at similar rates. Cultures representing five genera of the SRB (Desulfovibrio desulfuricans, Desulfobulbus propionicus, Desulfococcus multivorans, Desulfobacter sp. strain BG-8, and Desulfobacterium sp. strain BG-33) were grown in a strictly anoxic, minimal medium that received a dose of inorganic Hg 120 h after inoculation. The mercury methylation rates (MMR) normalized per cell were up to 3 orders of magnitude higher in pure cultures of members of SRB groups capable of acetate utilization (e.g., the family Desulfobacteriaceae) than in pure cultures of members of groups that are not able to use acetate (e.g., the family Desulfovibrionaceae). Little or no Hg methylation was observed in cultures of Desulfobacterium or Desulfovibrio strains in the absence of sulfate, indicating that Hg methylation was coupled to respiration in these strains. Mercury methylation, sulfate reduction, and the identities of sulfate-reducing bacteria in marine sediment slurries were also studied. Sulfate-reducing consortia were identified by using group-specific oligonucleotide probes that targeted the 16S rRNA molecule. Acetate-amended slurries, which were dominated by members of the Desulfobacterium and Desulfobacter groups, exhibited a pronounced ability to methylate Hg when the MMR were normalized to the SRR, while lactate-amended and control slurries had normalized MMR that were not statistically different. Collectively, the results of pure-culture and amended-sediment experiments suggest that members of the family Desulfobacteriaceae have a greater potential to methylate Hg than members of the family Desulfovibrionaceae have when the MMR are normalized to the SRR. Hg methylation potential may be related to genetic composition and/or carbon metabolism in the SRB. Furthermore, we found that in marine sediments that are rich in organic matter and dissolved sulfide rapid CH(3)Hg accumulation is coupled to rapid sulfate reduction. The observations described above have broad implications for understanding the control of CH(3)Hg formation and for developing remediation strategies for Hg-contaminated sediments.
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Affiliation(s)
- J K King
- Skidaway Institute of Oceanography, Savannah, Georgia 31411, USA
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