Journal
FEMS MICROBIOLOGY ECOLOGY
Volume 87, Issue 1, Pages 52-63Publisher
OXFORD UNIV PRESS
DOI: 10.1111/1574-6941.12189
Keywords
High Arctic; merA; mercury resistance; plasmids; horizontal transfer
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Funding
- Danish Agency of Science [645-06-0233]
- U.S. National Science Foundation [EAR-0433793, EAR1123689]
- U.S. Department of Energy [DE-FG02-05ER63969]
- NASA Exobiology and Evolutionary Biology Program [NNX10AT31G]
- Division Of Earth Sciences
- Directorate For Geosciences [1123689] Funding Source: National Science Foundation
- NASA [123884, NNX10AT31G] Funding Source: Federal RePORTER
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Bacterial reduction in Hg2+ to Hg-0, mediated by the mercuric reductase (MerA), is important in the biogeochemical cycling of Hg in temperate environments. Little is known about the occurrence and diversity of merA in the Arctic. Seven merA determinants were identified among bacterial isolates from High Arctic snow, freshwater and sea-ice brine. Three determinants in Bacteriodetes, Firmicutes and Actinobacteria showed <92% (amino acid) sequence similarity to known merA, while one merA homologue in Alphaproteobacteria and 3 homologues from Betaproteobacteria and Gammaproteobacteria were >99% similar to known merA's. Phylogenetic analysis showed the Bacteroidetes merA to be part of an early lineage in the mer phylogeny, whereas the Betaproteobacteria and Gammaproteobacteria merA appeared to have evolved recently. Several isolates, in which merA was not detected, were able to reduce Hg2+, suggesting presence of unidentified merA genes. About 25% of the isolates contained plasmids, two of which encoded mer operons. One plasmid was a broad host-range IncP- plasmid. No known incompatibility group could be assigned to the others. The presence of conjugative plasmids, and an incongruent distribution of merA within the taxonomic groups, suggests horizontal transfer of merA as a likely mechanism for High Arctic microbial communities to adapt to changing mercury concentration.
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