Methanobactin (MB) from M. trichosporium OB3b (OB3b-MB) can substantially increase methylmercury (MeHg) production by anaerobic bacteria, such as (a) D. desulfuricans ND132 and (b) G. sulfurreducens PCA. [Reprinted by permission from Yin, X., et al. 2020. “Synergistic effects of a chalkophore, methanobactin, on microbial methylation of mercury.” Applied & Environmental Microbiology. 86(11): e00122–20. DOI: 10.1128/AEM.00122-20.]
Substantially enhanced mercury methylation is observed with some forms of methanobactin produced by some methanotrophs, but not by others
Microbial production of MeHg, a neurotoxin, is a great health and environmental concern as it can bioaccumulate and biomagnify in the food web. A chalkophore or a copper-binding compound, termed methanobactin (MB), has been shown to form strong complexes with Hg(II) and also enables some methanotrophs to degrade MeHg. Unknown, however, is whether Hg(II) binding with MB can also impede Hg(II) methylation by other microbes. Contrary to expectations, MB produced by the methanotroph Methylosinus trichosporium OB3b (OB3b-MB) enhanced the rate and efficiency of Hg(II) methylation more than that observed with thiol compounds (such as cysteine) by the Hg-methylating bacteria D. desulfuricans ND132 and G. sulfurreducens PCA. Compared to no-MB controls, OB3b-MB decreased the rates of Hg(II) sorption and internalization, but increased methylation by five to seven fold, suggesting that Hg(II) complexation with OB3b-MB facilitated exchange and internal transfer of Hg(II) to the HgcAB proteins required for methylation. Conversely, addition of excess amounts of OB3b-MB or a different form of MB from Methylocystis strain SB2 (SB2-MB) inhibited Hg(II) methylation, likely due to greater binding of Hg(II).
Collectively, these results underscore the complex roles of exogenous metal-scavenging compounds produced by methanotrophs in controlling net MeHg production and bioaccumulation in the environment.
Although the genetic basis of Hg methylation is known, factors that control net MeHg production in the environment are poorly understood. We show that Hg methylation can be substantially enhanced by one form of an exogenous copper-binding compound (MB) produced by some methanotrophs, but not by another. This novel finding illustrates that complex interactions exist between microbes and that these interactions can potentially affect net MeHg production in situ.
Yin, X., L. Wang, L. Zhang, H. Chen, X. Liang, X. Lu, A. A. DiSpirito, J. D. Semrau, and B. Gu. 2020. “Synergistic effects of a chalkophore, methanobactin, on microbial methylation of mercury.” Applied & Environmental Microbiology. 86(11): e00122-20. DOI: 10.1128/AEM.00122-20.
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