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Biogeochemistry: Mercury methylation on ice

Nature Microbiology volume 1, Article number: 16165 (2016) Cite this article

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Metagenomic analysis of Antarctic sea-ice and brine reveals the presence of hgcAB-like genes in the microaerophilic marine bacterium Nitrospina. These are similar to ones responsible for mercury methylation in anaerobic microorganisms and provide a plausible mechanism for mercury methylation in oxic marine environments.

In 2013, nations of the world agreed on the first global treaty to curb anthropogenic mercury (Hg) release into the environment. One of the main goals of this agreement was to mitigate the many deleterious health outcomes associated with methylmercury (CH3HgI) exposure1. Divalent inorganic mercury (HgII) is converted by microorganisms into CH3HgI, which is biomagnified in apex marine predators such as tunas and cetaceans to a millionfold higher concentration than seawater, levels that can be toxic for both humans and wildlife1. 2013 also marked a scientific breakthrough when researchers began to “crack the mercury methylation code” by identifying a two-gene cluster (hgcA and hgcB) in microorganisms involved in Hg methylation2,3. The hgcA gene encodes for a putative corrinoid protein capable of transferring a methyl group to HgII. The HgcB protein returns HgcA to a redox state that enables it to receive a new methyl group2. The presence of these genes has so far been restricted to anaerobic sulfate and iron-reducing bacteria and methanogens4, leaving researchers wondering how to explain high CH3HgI concentrations and active methylation of HgII observed in oxic marine waters5,6.

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Figure 1: Proposed mechanism by Parks et al.2 for the role of the HgcAB proteins in methylation of inorganic Hg (HgII).

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Authors and Affiliations

  1. Elsie M. Sunderland and Amina T. Schartup are in the Harvard John A. Paulson School of Engineering and Applied Sciences, Cambridge, Massachusetts 02138, USA,

    Elsie M. Sunderland & Amina T. Schartup

  2. the Harvard T.H. Chan School of Public Health, Boston, Massachusetts 02215, USA.,

    Elsie M. Sunderland & Amina T. Schartup

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  1. Elsie M. Sunderland
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  2. Amina T. Schartup
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Correspondence to Elsie M. Sunderland.

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Sunderland, E., Schartup, A. Biogeochemistry: Mercury methylation on ice. Nat Microbiol 1, 16165 (2016). https://doi.org/10.1038/nmicrobiol.2016.165

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