Methylmercury Resistance in
            <i>Desulfovibrio desulfuricans</i>
            Strains in Relation to Methylmercury Degradation

Baldi, Franco; Pepi, Milva; Filippelli, Marco

doi:10.1128/aem.59.8.2479-2485.1993

Cited by 91 publications

(63 citation statements)

References 33 publications

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“…Given the infinite range of values possible for the ORDP ratio, however, assignment of relative degrees of involvement of sulfate reduction versus methanogenesis is a futile exercise, even when modified along the lines of ''respiratory indices'' used in studies of methanogenesis in sediments (56). This difficulty arises because this line of reasoning ignores the possibility of 14 CH 4 production from [ 14 C]MeHg being carried out by nonmethanogens, which could include detoxification reactions by certain sulfate reducers (5) as well as by anaerobic sediment organisms possessing the organomercurial lyase enzymes. The results from the laboratory sediment incubations generally reinforce the above conclusion with regard to the involvement of sulfate reduction and methanogenesis in oxidative demethylation.…”

Section: Discussionmentioning

confidence: 99%

“…However, although both 14 CH 4 and 14 CO 2 were detected in cultures of methanogens, sulfate reducers formed only 14 CH 4 from [ 14 C]MeHg and oxidative demethylation in sulfate-reducing bacterium cultures remains to be demonstrated (38). A non-lyase-associated formation of methane from MeHg was recently reported to exist in methylmercury-resistant cultures of Desulfovibrio desulfuricans (5). The methane was believed to have resulted from the breakdown of dimethylmercury sulfide which accumulated during growth.…”

mentioning

confidence: 98%

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Methylmercury oxidative degradation potentials in contaminated and pristine sediments of the carson river, nevada

Oremland¹,

Miller²,

Dowdle³

et al. 1995

Appl Environ Microbiol

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Sediments from mercury-contaminated and uncontaminated reaches of the Carson River, Nevada, were assayed for sulfate reduction, methanogenesis, denitrification, and monomethylmercury (MeHg) degradation. Demethylation of [ 14 C]MeHg was detected at all sites as indicated by the formation of 14 CO 2 and 14 CH 4. Oxidative demethylation was indicated by the formation of 14 CO 2 and was present at significant levels in all samples. Oxidized/reduced demethylation product ratios (i.e., 14 CO 2 / 14 CH 4 ratios) generally ranged from 4.0 in surface layers to as low as 0.5 at depth. Production of 14 CO 2 was most pronounced at sediment surfaces which were zones of active denitrification and sulfate reduction but was also significant within zones of methanogenesis. In a core taken from an uncontaminated site having a high proportion of oxidized, coarsegrain sediments, sulfate reduction and methanogenic activity levels were very low and 14 CO 2 accounted for 98% of the product formed from [ 14 C]MeHg. There was no apparent relationship between the degree of mercury contamination of the sediments and the occurrence of oxidative demethylation. However, sediments from Fort Churchill, the most contaminated site, were most active in terms of demethylation potentials. Inhibition of sulfate reduction with molybdate resulted in significantly depressed oxidized/reduced demethylation product ratios, but overall demethylation rates of inhibited and uninhibited samples were comparable. Addition of sulfate to sediment slurries stimulated production of 14 CO 2 from [ 14 C]MeHg, while 2-bromoethanesulfonic acid blocked production of 14 CH 4. These results reveal the importance of sulfate-reducing and methanogenic bacteria in oxidative demethylation of MeHg in anoxic environments.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 98%

Methylmercury oxidative degradation potentials in contaminated and pristine sediments of the carson river, nevada

Oremland¹,

Miller²,

Dowdle³

et al. 1995

Appl Environ Microbiol

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“…The microbial production of dimethylmercury (diMeHg), although proposed initially [54], has not been unequivocally demonstrated to date. The production of diMeHg from monoMeHg [67] by disproportionation in H 2 S-rich environments [68] might be the mechanism by which SRB form diMeHg during sul¢dogenic growth [69]. Recent reports of high levels of di-MeHg in aerial £uxes from oceanic upwelling sites [70] (N. Bloom, personal communication) and terrestrial [71] sources warrant a closer look at the mechanisms by which diMeHg is formed.…”

Section: Ionic Mercury [Hg(ii)] Methylationmentioning

confidence: 99%

Bacterial mercury resistance from atoms to ecosystems

2003

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Bacterial resistance to inorganic and organic mercury compounds (HgR) is one of the most widely observed phenotypes in eubacteria. Loci conferring HgR in Gram-positive or Gram-negative bacteria typically have at minimum a mercuric reductase enzyme (MerA) that reduces reactive ionic Hg(II) to volatile, relatively inert, monoatomic Hg(0) vapor and a membrane-bound protein (MerT) for uptake of Hg(II) arranged in an operon under control of MerR, a novel metal-responsive regulator. Many HgR loci encode an additional enzyme, MerB, that degrades organomercurials by protonolysis, and one or more additional proteins apparently involved in transport. Genes conferring HgR occur on chromosomes, plasmids, and transposons and their operon arrangements can be quite diverse, frequently involving duplications of the above noted structural genes, several of which are modular themselves. How this very mobile and plastic suite of proteins protects host cells from this pervasive toxic metal, what roles it has in the biogeochemical cycling of Hg, and how it has been employed in ameliorating environmental contamination are the subjects of this review.

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“…Both aerobes and anaerobes were shown to be capable of demethylating methylmercury via organomercurial lyase-mercuric reductase, encoded in the mer operon. The products are CH4 or CO2 and volatile mercury (1,11). However, little is known about the biochemistry of the formation of methylmercury.…”

mentioning

confidence: 99%

Enzymatic catalysis of mercury methylation by Desulfovibrio desulfuricans LS

Choi

Chase

Bartha

1994

Appl Environ Microbiol

122

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The recently defined role of methylcobalamin in Hg2+ methylation by Desulfovibrio desulfuricans LS enabled us to reexamine the question of whether the principal source of methylmercury is spontaneous transmethylation or an enzymatically catalyzed process. In cell extracts of D. desulfuricans LS, over 95% of the 57Co label was associated with macromolecules rather than with free cobalamin. Both gel filtration and electrophoresis of cell extracts identified a single corrinoid protein of 40 kDa in size. This finding, in combination with the previously reported light-reversible propyl iodide inhibition of the Hg2+ methylation process, led us to propose that this 40-kDa corrinoid protein is the in vivo methyl donor in D. desu6uricans LS. Under reducing conditions, cell extracts containing the corrinoid protein produced 14CH3Hg' from Hg2+ and 5-14CH3tetrahydrofolate with a maximum specific activity of 0.73 nmol min-1 mg of cell protein-1. The sequence of methyl transfer was from methyltetrahydrofolate to the corrinoid protein to Hg2+. The rate of methylation versus the Hg2+ concentration followed Michaelis-Menten kinetics, with an apparent Km of 0.87 mM HgCl2. The activity was oxygen sensitive, and Hg2+ methylation was optimal at 35°C and pH 6.5. The observation of saturation kinetics and the 600-fold-higher rate of Hg2+ methylation (at pH 7.0) by cell extracts, compared with transmethylation by free methylcobalamin, proved that in vivo Hg2+ methylation is an enzymatically catalyzed process.

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Methylmercury Resistance in Desulfovibrio desulfuricans Strains in Relation to Methylmercury Degradation

Cited by 91 publications

References 33 publications

Methylmercury oxidative degradation potentials in contaminated and pristine sediments of the carson river, nevada

Methylmercury oxidative degradation potentials in contaminated and pristine sediments of the carson river, nevada

Bacterial mercury resistance from atoms to ecosystems

Enzymatic catalysis of mercury methylation by Desulfovibrio desulfuricans LS

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