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Methanogens and iron-reducing bacteria: the overlooked members of mercury-methylating microbial communities in boreal lakes
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2018 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 84, no 23, article id e01774-18Article in journal (Refereed) Published
Abstract [en]

ABSTRACT: Methylmercury is a potent human neurotoxin which biomagnifies in aquatic food webs. Although anaerobic microorganisms containing the hgcA gene potentially mediate the formation of methylmercury in natural environments, the diversity of these mercury-methylating microbial communities remains largely unexplored. Previous studies have implicated sulfate-reducing bacteria as the main mercury methylators in aquatic ecosystems. In the present study, we characterized the diversity of mercury-methylating microbial communities of boreal lake sediments using high-throughput sequencing of 16S rRNA and hgcA genes. Our results show that in the lake sediments, Methanomicrobiales and Geobacteraceae also represent abundant members of the mercury-methylating communities. In fact, incubation experiments with a mercury isotopic tracer and molybdate revealed that only between 38% and 45% of mercury methylation was attributed to sulfate reduction. These results suggest that methanogens and iron-reducing bacteria may contribute to more than half of the mercury methylation in boreal lakes.

IMPORTANCE: Despite the global awareness that mercury, and methylmercury in particular, is a neurotoxin to which millions of people continue to be exposed, there are sizable gaps in the understanding of the processes and organisms involved in methylmercury formation in aquatic ecosystems. In the present study, we shed light on the diversity of the microorganisms responsible for methylmercury formation in boreal lake sediments. All the microorganisms identified are associated with the processing of organic matter in aquatic systems. Moreover, our results show that the well-known mercury-methylating sulfate-reducing bacteria constituted only a minor portion of the potential mercury methylators. In contrast, methanogens and iron-reducing bacteria were important contributors to methylmercury formation, highlighting their role in mercury cycling in the environment.

Place, publisher, year, edition, pages
American Society for Microbiology , 2018. Vol. 84, no 23, article id e01774-18
Keywords [en]
mercury, methylation, hgcA gene, 16S rRNA gene, boreal lakes, methanogens, iron-reducing bacteria, sulfate-reducing bacteria
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-154035DOI: 10.1128/AEM.01774-18ISI: 000450438700007PubMedID: 30242005OAI: oai:DiVA.org:umu-154035DiVA, id: diva2:1272840
Funder
Swedish Research Council, 2011-7192Swedish Research Council, 2012-3892Swedish Research Council Formas, 2012-986The Kempe Foundations, SMK-2840Available from: 2018-12-20 Created: 2018-12-20 Last updated: 2018-12-20Bibliographically approved

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Bouchet, SylvainTolu, JulieBjörn, Erik

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