Tag: Mercury

Bacterial mercury resistance from atoms to ecosystems

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Author: Barkay, T; Miller, SM; Summers, AO Description: 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,…

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Effect of divalent metals on Hg(II) uptake and methylation by bacteria

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Author: Schaefer, JK; Szczuka, A; Morel, FM Description: 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…

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Sulfurization of Dissolved Organic Matter Increases Hg-Sulfide-Dissolved Organic Matter Bioavailability to a Hg-Methylating Bacterium

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Author: Graham, AM; Cameron-Burr, KT; Hajic, HA; Lee, C; Msekela, D; Gilmour, CC Description: Reactions of dissolved organic matter (DOM) with aqueous sulfide (termed sulfurization) in anoxic environments can substantially increase DOM’s reduced sulfur functional group content. Sulfurization may affect DOM-trace metal interactions, including complexation and metal-containing particle precipitation, aggregation, and dissolution. Using a diverse suite of DOM samples, we found that susceptibility to additional sulfur incorporation via reaction with aqueous sulfide increased with increasing DOM aromatic-, carbonyl-, and carboxyl-C content. The role of DOM sulfurization in enhancing Hg bioavailability…

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Anaerobic Mercury Methylation and Demethylation by Geobacter bemidjiensis Bem

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Author: Lu, X; Liu, Y; Johs, A; Zhao, L; Wang, T; Yang, Z; Lin, H; Elias, DA; Pierce, EM; Liang, L; Barkay, T; Gu, B Description: Microbial methylation and demethylation are two competing processes controlling the net production and bioaccumulation of neurotoxic methylmercury (MeHg) in natural ecosystems. Although mercury (Hg) methylation by anaerobic microorganisms and demethylation by aerobic Hg-resistant bacteria have both been extensively studied, little attention has been given to MeHg degradation by anaerobic bacteria, particularly the iron-reducing bacterium Geobacter bemidjiensis Bem. Here we report, for the first time,…

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Emerging investigator series: methylmercury speciation and dimethylmercury production in sulfidic solutions

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Author: Kanzler, CR; Lian, P; Trainer, EL; Yang, X; Govind, N; Parks, JM; Graham, AM Description: Alkylated mercury species (monomethylmercury, MeHg, and dimethylmercury, DMeHg) exhibit significant bioaccumulation, and pose significant risks to ecosystems and human health. Although decades of research have been devoted to understanding MeHg formation and degradation, little is known about the DMeHg formation in aquatic systems. Here, we combine complementary experimental and computational approaches to examine MeHg speciation and DMeHg formation in sulfidic aqueous solutions, with an emphasis on the formation and decomposition of the binuclear bis(methylmercuric(ii))…

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Mercury and methyl mercury in fishes from Bacaja River (Brazilian Amazon): evidence for bioaccumulation and biomagnification

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Author: Souza-Araujo, J; Giarrizzo, T; Lima, MO; Souza, MB Description: This study assessed total mercury (THg) and methyl mercury (MeHg) concentrations, bioaccumulation and biomagnification of THg through the food web in fishes consumed by indigenous communities of Bacaja River, the largest tributary of the right bank of Xingu River. In total, 496 fish (22 species) were sampled. Nine species had THg concentrations above the limit recommended by the World Health Organisation (0.5 microg g(-1) wet mass), and one exceeded the recommended level for Hg in predatory fishes by Brazilian law…

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Influences of watershed characteristics on mercury levels in Wisconsin rivers

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Author: Hurley, JP; Benoit, JM; Babiarz, CL; Shafer, MM; Andren, AW; Sullivan, JR; Hammond, R; Webb, DA Description: Total and monomethyl mercury were measured at 39 river sites in Wisconsin during fall 1992 and spring 1993. Using a Geographic Information System (GIS), we delineated watersheds with unique and homogeneous physical characteristics. Mean unfiltered total Hg (HgT) was higher in spring (7.94 ng L-1) than in fall (3.45 ng L-1). Major differences in HgT yields were observed among various land-use groupings. In wetland/forest watersheds, elevated HgT fluxes were associated with the…

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Mercury methylation and methylmercury demethylation in boreal lake sediment with legacy sulphate pollution

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Author: Huang, H; Mangal, V; Rennie, MD; Tong, H; Simpson, MJ; Mitchell, CPJ Description: Sulphate and dissolved organic matter (DOM) in freshwater systems may regulate the formation of methylmercury (MeHg), a potent neurotoxin that biomagnifies in aquatic ecosystems. While many boreal lakes continue to recover from decades of elevated atmospheric sulphate deposition, little research has examined whether historically high sulphate concentrations can result in persistently elevated MeHg production and accumulation in aquatic systems. This study used sediment from a historically sulphate-impacted lake and an adjacent reference lake in northwestern Ontario,…

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Methylmercury decomposition in sediments and bacterial cultures: involvement of methanogens and sulfate reducers in oxidative demethylation

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Author: Oremland, R. S.; Culbertson, C. W.; Winfrey, M. R. Description: Demethylation of monomethylmercury in freshwater and estuarine sediments and in bacterial cultures was investigated with CH(3)HgI. Under anaerobiosis, results with inhibitors indicated partial involvement of both sulfate reducers and methanogens, the former dominating estuarine sediments, while both were active in freshwaters. Aerobes were the most significant demethylators in estuarine sediments, but were unimportant in freshwater sediments. Products of anaerobic demethylation were mainly CO(2) as well as lesser amounts of CH(4). Acetogenic activity resulted in fixation of some CO(2) produced…

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Simultaneous determination of mercury methylation and demethylation capacities of various sulfate-reducing bacteria using species-specific isotopic tracers

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Author: Bridou, Romain; Monperrus, Mathilde; Gonzalez, Pablo Rodriguez; Guyoneaud, Remy; Amouroux, David Description: The use of species-specific isotopic tracers for inorganic and methyl mercury has allowed the simultaneous determination of the methylation and demethylation potentials of pure culture of isolated sulfate-reducing (SR) bacterial strains using low Hg species concentration levels (7 µg/L (199)Hg(II), 1 µg/L Me(201)Hg). A major advantage of the method reported here is that it can be used to follow simultaneously both the degradation of the species added but also the formation of their degradation products and thus…

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