Abstract
Natural dissolved organic matter (DOM) affects mercury (Hg) redox reactions and anaerobic microbial methylation in the environment. Several studies have shown that DOM can enhance Hg methylation, especially under sulfidic conditions, whereas others show that DOM inhibits Hg methylation due to strong Hg-DOM complexation. In this study, we investigated and compared the effects of DOM on Hg methylation by an iron-reducing bacterium Geobacter sulfurreducens PCA and a sulfate-reducing bacterium Desulfovibrio desulfuricans ND132 under nonsulfidic conditions. The methylation experiment was performed with washed cells either in the absence or presence of DOM or glutathione, both of which form strong complexes with Hg via thiol-functional groups. DOM was found to greatly inhibit Hg methylation by G. Sulfurreducens PCA but enhance Hg methylation by D. desulfuricans ND132 cells with increasing DOM concentration. These strain-dependent opposing effects of DOM were also observed with glutathione, suggesting that thiols in DOM likely played an essential role in affecting microbial Hg uptake and methylation. Additionally, DOM and glutathione greatly decreased Hg sorption by G. sulfurreducens PCA but showed little effect on D. desulfuricans ND132 cells, demonstrating that ND132 has a higher affinity to sorb or take up Hg than the PCA strain. These observations indicate that DOM effects on Hg methylation are bacterial strain specific, depend on the DOM:Hg ratio or site-specific conditions, and may thus offer new insights into the role of DOM in methylmercury production in the environment.
Original language | English |
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Pages (from-to) | 10468-10475 |
Number of pages | 8 |
Journal | Environmental Science and Technology |
Volume | 51 |
Issue number | 18 |
DOIs | |
State | Published - Sep 19 2017 |
Funding
We thank Xiangping Yin for assistance with mercury and methylmercury analyses, Rosalie Chu for FTICR-MS analysis, and Phuong Pham for EFPC-DOM isolation. This research was sponsored by the Office of Biological and Environmental Research (BER), Office of Science, US Department of Energy (DOE) as part of the Mercury Science Focus Area at Oak Ridge National Laboratory (ORNL), which is managed by UT-Battelle LLC for the DOE under contract DE-AC05-00OR22725. The FTICR-MS analysis was performed at Environmental Molecular Science Laboratory (EMSL), a DOE Office of Science User Facility sponsored by BER at Pacific Northwest National Laboratory.