Coupled Mercury–Cell Sorption, Reduction, and Oxidation on Methylmercury Production by Geobacter sulfurreducens PCA

Journal Article · Tue Sep 30 00:00:00 EDT 2014 · Environmental Science and Technology

DOI:https://doi.org/10.1021/es502537a· OSTI ID:1286719

Lin, Hui ^[1]; Morrell-Falvey, Jennifer L. ^[2]; Rao, Balaji ^[1]; Liang, Liyuan ^[1]; Gu, Baohua ^[1]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Environmental Sciences Division
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division

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), in this paper 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 Zn²⁺ leads to increased Hg reduction and decreased methylation. Finally, 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.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1286719
• Journal Information: Environmental Science and Technology, Vol. 48, Issue 20; ISSN 0013-936X
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES