Methylmercury Uptake and Degradation by Methanotrophs

Abstract

Methylmercury (CH3Hg+) is a potent neurotoxin produced by certain anaerobic microorganisms in natural environments. While numerous studies have characterized the basis of mercury methylation, no studies have examined CH3Hg+ degradation by methanotrophs, despite their ubiquitous presence in the environment. We report that some methanotrophs (e.g., Methylosinus trichosporium OB3b) can take up and degrade CH3Hg+ rapidly, whereas others (e.g., Methylococcus capsulatus Bath) can take up but not degrade CH3Hg+. Demethylation by M. trichosporium OB3b increases with increasing CH3Hg+ concentrations but is abolished in mutants deficient in methanobactin biosynthesis. Further, addition of methanol as a competing C1 substrate inhibits demethylation, suggesting that CH3Hg+ degradation by methanotrophs may involve an initial bonding of CH3Hg+ by methanobactin followed by cleavage of the C–Hg bond in CH3Hg+ by the methanol dehydrogenase. This new demethylation pathway by methanotrophs indicates possible broader involvement of C1-metabolizing aerobes in the environmental degradation of toxic CH3Hg+.