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Mercury methylating microbial communities in boreal wetlands
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
School of Science and Technology, Örebro University, Örebro, Sweden. (School of Science and Technology, Örebro University, SE-701 82 Örebro, Sweden)
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.ORCID iD: 0000-0002-4265-1835
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Understanding the formation of the potent neurotoxic methylmercury (MeHg) is a major concern due to its threats to wildlife and human health. As boreal wetlands play a crucial role for Hg cycling on a global scale, it is crucial to understand the biogeochemical processes involved in MeHg formation in this landscape. A strategy combining high-throughput hgcA amplicon sequencing with molecular barcoding was used to revealed diverse clades of Hg(II) methylators in a wide range of wetland soils. Our results confirms a predominant role of Deltaproteobacteria, and in particular Geobacteraceae, as important Hg(II) methylators in boreal wetland soils. Firmicutes, and in particular Ruminococcaceae, were also abundant members of the Hg(II) methylating microbial communities. Our survey highlight the importance of nutrient status for the shaping of Hg(II) methylating communities across the four wetlands and reveal that water content and prevailing redox states are key factors determining the local variation in Hg(II) methylating community composition within individual wetlands. Also, our study suggests that high nutrient levels linked to low redox potential seemed to favour Hg(II) methylating methanogens within the Methanoregulaceae. Our findings expand the current knowledge on the Hg(II) methylating microbial community composition in wetland soils and the geochemical factors underpinning spatial heterogeity in such communities.  

Keyword [en]
Wetlands, Methylmercury, Mercury methylation, hgcA, Community composition, Bacteria
National Category
Genetics
Research subject
Biology with specialization in Limnology
Identifiers
URN: urn:nbn:se:uu:diva-346177OAI: oai:DiVA.org:uu-346177DiVA, id: diva2:1190709
Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2018-03-15Bibliographically approved
In thesis
1. Remediation of mercury contaminated soil and biological mercury methylation in the landscape
Open this publication in new window or tab >>Remediation of mercury contaminated soil and biological mercury methylation in the landscape
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Accumulation of mercury (Hg) in soil originating from both natural and anthropogenic sources poses a major hazard to environmental and human health. Inorganic Hg(II) in soil can be transformed to highly toxic methylmercury (MeHg) mainly via methylating microorganisms. Although MeHg constitutes less than 2% of total Hg in soil, it enters aquatic systems through runoff and can be subsequently bioaccumulated along the food chain, thereby causing severe harm to humans.

Current major remediation techniques to control soil Hg contamination were reviewed. Organic matter, clay/minerals and complexation ligands within soil are principal factors influencing Hg mobility that is crucial for evaluating and optimising remedial techniques. The potential of soil washing to treat soil Hg contamination was evaluated. The studied soil was fractionated from fine to coarse particles to assess the effectiveness of physical separation. Batch leaching and pH-static titration tests were performed using (1) water, (2) EDTA, (3) NaOH, (4) HCl, (5) acidic leachates from biodegradable wastes, and (6) alkaline leachates from fly/bottom ashes, to estimate the efficiency of chemical extraction. Less than 1.5% of the total Hg could be mobilised after combined treatments, implying very tight binding of Hg to soil particles, thereby hampering soil washing as a strategy for the studied soil.

Hg(II) methylation in boreal soils and lake sediments can have major consequences for MeHg inputs to downstream aquatic systems. It is therefore important to understand the biogeochemical mechanisms involved in MeHg formation in these landscapes. The microbes involved in Hg(II) methylation in sediments and boreal forests and wetlands were investigated by high-throughput 16S rRNA and hgcA sequencing with molecular barcoding. In all three environments, hgcA sequences were distributed among Proteobacteria, Firmicutes and Euryarchaeota, and Deltaproteobacteria, particularly Geobacteraceae, appeared to play a predominant role. Ruminococcaceae were also abundant Hg(II) methylators in soils from one forest and all the wetlands. The boreal forest survey provided some first insights about the possible link between MeHg formation and non-Hg(II) methylating bacterial communities that likely support the growth and activity of Hg(II) methylating members. Results from wetlands pointed out nutrient status as an important factor shaping Hg(II) methylating communities across the four wetlands, and highlighted a significant role of water content and iron in controlling the distribution of Hg(II) methylators within individual wetlands. Furthermore, the interactions between Hg(II) methylating groups revealed that the more anaerobic and productive conditions seemed to favour the activity of Methanoregulaceae and hamper the growth of Ruminococcaceae. Results from lake sediments supported that Geobacteraceae have an important role in Hg(II) methylation under ferruginous geochemical conditions. Our findings provide a better understanding of Hg(II) methylating communities in the landscape.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 57
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1643
Keyword
Mercury contamination, Soil remediation, Methylmercury, Mercury methylation, hgcA, Community composition, Bacteria, Landscape
National Category
Environmental Sciences
Research subject
Biology with specialization in Microbiology
Identifiers
urn:nbn:se:uu:diva-345626 (URN)978-91-513-0267-6 (ISBN)
Public defence
2018-04-27, Hambergssalen, Villavägen 16, Uppsala, 09:00 (English)
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Supervisors
Available from: 2018-04-06 Created: 2018-03-10 Last updated: 2018-04-24

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Jingying, XuBuck, MoritzBertilsson, StefanBravo, Andrea Garcia

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