Methylmercury (MeHg) toxin, formed by certain anaerobic bacteria, is thought to be rapidly excreted from cells, but this process has been poorly studied and its mechanism remains unclear. We found that MeHg export is bacteria specific and thiol-concentration dependent. In the absence of thiol ligands, MeHg is strongly sorbed by Geobacter sulfurreducens PCA, but not by Desulfovibrio desulfuricans ND132 cells. The presence of thiols such as cysteine can greatly facilitate MeHg desorption and export by cells.
Our results provide fundamental understandings on how MeHg is transported out of bacterial cells and what environmental factors may control desorption and cell export of MeHg. We suggest important roles of complexing ligands, such as natural organic matter, in MeHg production and mobilization in the environment.
Researchers studied factors affecting MeHg export and its distribution in cells, on cell surfaces, and in solution by two known mercury methylators, Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. Thiols, such as cysteine, were found to greatly facilitate desorption and export of MeHg, particularly by PCA cells. In cysteine-free assays (4 h), <10% of the synthesized MeHg was found in solution, >90% was associated with PCA, of which ~73% was sorbed on the cell surface and 19% remained inside the cells. In comparison, 77% MeHg was in solution, leaving ~13% of the MeHg sorbed and ~10% inside the ND132 cells. Results demonstrate that MeHg export is bacteria specific, time dependent, and influenced by thiols—implicating important roles of ligands, such as natural organic matter, in MeHg production and mobilization in the environment.
Lin, H., X. Lu, L. Y. Liang, and B. H. Gu. 2015. “Thiol-Facilitated Cell Export and Desorption of Methylmercury by Anaerobic Bacteria.” Environmental Science & Technology Letters 2(10): 292-296. DOI: 10.1021/acs.estlett.5b00209.
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