Methylmercury uptake and degradation by methanotrophs.

Methylmercury (CHHg) is a potent neurotoxin produced by certain anaerobic microorganisms in natural environments. Although numerous studies have characterized the basis of mercury (Hg) methylation, no studies have examined CHHg degradation by methanotrophs, despite their ubiquitous presence in the environment. We report that some methanotrophs, such as OB3b, can take up and degrade CHHg rapidly, whereas others, such as Bath, can take up but not degrade CHHg. Demethylation by OB3b increases with increasing CHHg concentrations but was abolished in mutants deficient in the synthesis of methanobactin, a metal-binding compound used by some methanotrophs, such as OB3b. Furthermore, addition of methanol (>5 mM) as a competing one-carbon (C1) substrate inhibits demethylation, suggesting that CHHg degradation by methanotrophs may involve an initial bonding of CHHg by methanobactin followed by cleavage of the C-Hg bond in CHHg by the methanol dehydrogenase. This new demethylation pathway by methanotrophs indicates possible broader involvement of C1-metabolizing aerobes in the degradation and cycling of toxic CHHg in the environment.