The Genetic Basis for Bacterial Mercury Methylation

Abstract

Methylmercury is a potent neurotoxin produced in natural environments from inorganic mercury by anaerobic bacteria. However, until now the genes and proteins involved have remained unidentified. Here, we report a two-gene cluster, hgcA and hgcB, required for mercury methylation by Desulfovibrio desulfuricans ND132 and Geobacter sulfurreducens PCA. In either bacterium, deletion of hgcA, hgcB, or both genes abolishes mercury methylation. The genes encode a putative corrinoid protein, HgcA, and a 2[4Fe-4S] ferredoxin, HgcB, consistent with roles as a methyl carrier and an electron donor required for corrinoid cofactor reduction, respectively. Among bacteria and archaea with sequenced genomes, gene orthologs are present in confirmed methylators but absent in nonmethylators, suggesting a common mercury methylation pathway in all methylating bacteria and archaea sequenced to date.

Dietary input of microbes and host genetic variation shape among-population differences in stickleback gut microbiota

“…First, arriving microbes must have an appropriate spatial and nutritional niche within the host gut (Laparra and Sanz, 2010;Faith et al, 2011;Nicholson et al, 2012). In particular, host food composition affects the persistence of extant microbes through nutritional inputs needed to sustain microbial reproduction (Hildebrandt et al, 2009;Wu et al, 2011;Parks et al, 2013). Second, food intake and digestion rates affect the speed of food passage through the gut and thus the rate at which microbes are lost via excretion.…”

Patterns of Bacterial Diversity Along a Long-Term Mercury-Contaminated Gradient in the Paddy Soils

“…The resistance of bacteria to inorganic Hg 2+ is associated with the presence of the Hg resistance gene (merA) [16,17], which has been considered widely distributed in the phyla of Firmicutes, Actinobacteria and Proteobacteria [16]. Meanwhile, ionic Hg in anaerobic habitats may also be potentially methylated to highly toxic methylmercury (MeHg) by Hg-methylating microbes [18,19], such as sulphate-reducing bacteria (SRB) [20,21], iron-reducing bacteria (FeRB) [22,23] and methanogens [24,25]. However, little is known regarding the responses of these Hg-methylating bacteria to long-term soil Hg contamination.…”

Mesmerized by mercury

“…However, a number of anaerobic microbes have the ability to transform inorganic mercury into methylmercury. Earlier this year the genes responsible for mercury methylation were identified, and it has now become possible to screen microbes for their ability to methylate mercury 3 . Methylmercury biomagnifies up aquatic and terrestrial food chains, reaching levels high enough to be toxic for animals feeding at high trophic levels -including predatory fish, fish-eating mammals and insect-eating birds.…”