Coupled Mercury鈥揅ell Sorption, Reduction, and Oxidation on Methylmercury Production by Geobacter sulfurreducens PCA

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• 作者：Hui Lin ; Jennifer L. Morrell-Falvey ; Balaji Rao ; Liyuan Liang ; Baohua Gu
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：October 21, 2014
• 年：2014
• 卷：48
• 期：20
• 页码：11969-11976
• 全文大小：420K
• ISSN：1520-5851

文摘

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 = 鈭?.62). These reactions depend on the Hg and cell concentrations or the ratio of Hg to cellular thiols (鈭扴H). Oxidation and methylation of Hg(0) are favored at relatively low Hg to cell鈥揝H molar ratios (e.g., <1). Increasing Hg to cell ratios from 0.25 脳 10^鈥?9 to 25 脳 10^鈥?9 moles-Hg/cell (equivalent to Hg/cell鈥揝H of 0.71 to 71) shifts the major reaction from oxidation to reduction. In the absence of five outer membrane c-type cytochromes, mutant 螖omcBESTZ 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. 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.