Abstract
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 methylmercury1-4. One strain of sulphate-reducing bacteria (Desulfovibrio
desulfuricans ND132) can also methylate elemental mercury5. 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 oxidise 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 oxidise and methylate
elemental mercury. In line with recent findings5, we show that Desulfovibrio desulfuricans
ND132 can both oxidise and methylate elemental mercury. However, the rate of
methylation of elemental mercury is only about one third the rate of methylation of
oxidized mercury. We also show that Desulfovibrio alaskensis G20 can oxidise, but not
methylate, elemental mercury. Geobacter sulfurreducens PCA is able to oxidise 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.
