Certain methanotrophs can take up and degrade toxic methylmercury.
We discovered that some methanotrophs can take up and degrade methylmercury (CH3Hg+) rapidly, whereas others can take up but not degrade CH3Hg+. Demethylation increases with increasing CH3Hg+ concentrations but was abolished in mutants deficient in the synthesis of methanobactin, or inhibited by methanol as a competing one-carbon substrate. A new demethylation pathway is proposed, which is remarkably different from the canonical organomercurial lyase pathway.
Methanotrophs likely play an important role in controlling net methylmercury production in situ. The work provides new insights into hitherto unknown, yet potentially widespread biological mechanisms of CH3Hg+ uptake and demethylation due to methanotrophs' prevalence in the environment.
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 such as Methylosinus trichosporium OB3b can take up and degrade CH3Hg+ rapidly, whereas others such as Methylococcus capsulatus Bath can take up but not degrade CH3Hg+. Demethylation by M. trichosporium OB3b increases with increasing CH3Hg+ concentrations but was abolished in mutants deficient in the synthesis of methanobactin, a metal-binding compound used by some methanotrophs such as M. trichosporium OB3b. Further, addition of methanol (> 5 mM) as a competing one-carbon (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 degradation and cycling of toxic CH3Hg+ in the environment.
Lu, X., W. Gu, L. Zhao, M. Farhan Ul Haque, A.A. DiSpirito, J.D. Semrau, and B. Gu. 2017. "Methylmercury Uptake and Degradation by Methanotrophs." Science Advances 3(5):e1700041. DOI:10.1126/sciadv.1700041.
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