Methylmercury is a neurotoxin that poses significant health risks to humans. Some anaerobic sulphate- and iron-reducing bacteria can methylate oxidized forms of mercury, generating methylmercury(1-4). One strain of sulphate-reducing bacteria (Desulfovibrio desulphuricans ND132) can also methylate elemental mercury(5). The prevalence of this trait among different bacterial strains and species remains unclear, however. Here, we compare the ability of two strains of the sulphate-reducing bacterium Desulfovibrio and one strain of the iron-reducing bacterium Geobacter to oxidize and methylate elemental mercury in a series of laboratory incubations. Experiments were carried out under dark, anaerobic conditions, in the presence of environmentally relevant concentrations of elemental mercury. We report differences in the ability of these organisms to oxidize and methylate elemental mercury. In line with recent findings(5), we show that D. desulphuricans ND132 can both oxidize and methylate elemental mercury. We find that the rate of methylation of elemental mercury is about one-third the rate of methylation of oxidized mercury. We also show that Desulfovibrio alaskensis G20 can oxidize, but not methylate, elemental mercury. Geobacter sulphurreducens PCA is able to oxidize and methylate elemental mercury in the presence of cysteine. We suggest that the activity of methylating and non-methylating bacteria may together enhance the formation of methylmercury in anaerobic environments.

Publication name	NATURE GEOSCIENCE  Volume: 6   Issue: 9   Pages: 751-754   Published: SEP 2013
Author(s)	Hu, Haiyan; Lin, Hui; Zheng, Wang; Tomanicek, Stephen J.; Johs, Alexander; Feng, Xinbin; Elias, Dwayne A.; Liang, Liyuan; Gu, Baohua
Corresponding author	GU Baohua  gub1@ornl.gov   Oak Ridge Natl Lab, Div Environm Sci, Oak Ridge, TN 37830 USA.
Author(s) from IGCAS	HU Haiyan, FENG Xinbin

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