Mercury methylation by metabolically versatile and cosmopolitan marine bacteria

Lin, H., Ascher, D. B., Myung, Y., Lamborg, C. H., Hallam, S. J., Gionfriddo, C. M., Holt, K. E. and Moreau, J. W. (2021) Mercury methylation by metabolically versatile and cosmopolitan marine bacteria. ISME Journal, 15(6), pp. 1810-1825. (doi: 10.1038/s41396-020-00889-4) (PMID:33504941)

Abstract

Microbes transform aqueous mercury (Hg) into methylmercury (MeHg), a potent neurotoxin that accumulates in terrestrial and marine food webs, with potential impacts on human health. This process requires the gene pair hgcAB, which encodes for proteins that actuate Hg methylation, and has been well described for anoxic environments. However, recent studies report potential MeHg formation in suboxic seawater, although the microorganisms involved remain poorly understood. In this study, we conducted large-scale multi-omic analyses to search for putative microbial Hg methylators along defined redox gradients in Saanich Inlet, British Columbia, a model natural ecosystem with previously measured Hg and MeHg concentration profiles. Analysis of gene expression profiles along the redoxcline identified several putative Hg methylating microbial groups, including Calditrichaeota, SAR324 and Marinimicrobia, with the last the most active based on hgc transcription levels. Marinimicrobia hgc genes were identified from multiple publicly available marine metagenomes, consistent with a potential key role in marine Hg methylation. Computational homology modelling predicts that Marinimicrobia HgcAB proteins contain the highly conserved amino acid sites and folding structures required for functional Hg methylation. Furthermore, a number of terminal oxidases from aerobic respiratory chains were associated with several putative novel Hg methylators. Our findings thus reveal potential novel marine Hg-methylating microorganisms with a greater oxygen tolerance and broader habitat range than previously recognized.

• Item Type: Articles
• Additional Information: HL was supported by a postgraduate fellowship from The University of Melbourne Environmental Microbiology Research Initiative. HL and JWM designed the project and wrote the paper in consultation with all co-authors. DBA supervised the protein homology modelling, supported by an Investigator Grant from the National Health and Medical Research Council (NHMRC) of Australia [GNT1174405], and by the Victorian Government OIS Program. CHL thanks Woods Hole Oceanographic Institution for support and Tracy Mincer for help and inspiration. KEH co-advised meta-omics and phylogenetic analyses, supported by a Senior Medical Research Fellowship from the Viertel Foundation of Australia. HL, DBH, YM, RW, KEH and JWM gratefully acknowledge the use of data generated under the auspices of the US Department of Energy (DOE) Joint Genome Institute and Office of Science User Facility, supported by the Office of Science of the U.S. Department of Energy under Contract DE-AC02- 05CH11231, the G. Unger Vetlesen and Ambrose Monell Foundations, and the Natural Sciences and Engineering Research Council of Canada through grants awarded to SJH.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Moreau, Dr John
• Authors: Lin, H., Ascher, D. B., Myung, Y., Lamborg, C. H., Hallam, S. J., Gionfriddo, C. M., Holt, K. E., and Moreau, J. W.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences > Earth Sciences
• Journal Name: ISME Journal
• Publisher: Nature Research
• ISSN: 1751-7362
• ISSN (Online): 1751-7370
• Published Online: 27 January 2021
• Copyright Holders: Copyright © 2021 The Authors
• First Published: First published in ISME Journal 15(6): 1810-1825
• Publisher Policy: Reproduced under a Creative Commons License