Microbial Community Composition and Methanotroph Diversity of a Subarctic Wetland in Russia

This study assessed the microbial diversity, activity, and composition of methane-oxidizing communities of a subarctic wetland in Russia,with mosaic cover of Sphagnum mosses and lichens of the genera Cladonia and Cetraria. Potential methane-oxidizing activity of peat sampled from lichen-dominated wetland sites was higher than that in the sites dominated by Sphagnum mosses. In peat from lichendominated sites, major bacterial groups identified by high-throughput sequencing of the 16S rRNA genes were the Acidobacteria (35.4-41.2% of total 16S rRNA gene reads), Alphaproteobacteria (19.1-24.2%), Gammaproteobacteria (7.9-11.1%), Actinobacteria (5.5-13.2%), Planctomycetes (7.2-9.5%), and Verrucomicrobia (5.1-9.5%). The distinctive feature of this community was high proportion of Subdivision 2 Acidobacteria, which are not char- acteristic for boreal Sphagnum peat bogs. Methanotrophic community composition was determined by mo- lecular analysis of the pmoA gene encoding particulate methane monooxygenase. Most (-80%) of all pmoA gene fragments revealed in peat from lichen-dominated sites belonged to the phylogenetic lineage represented by a microaerobic spiral-shaped methanotroph, "Candidatus Methylospira mobilis." Members of the genus Methylocystis, which are typical inhabitants of boreal Sphagnum peat bogs, represented only a minor group of indigenous methanotrophs. The specific feature of a methanotrophic community in peat from lichen-dominated sites was the presence of uncultivated USCa (Upland Soil Cluster alpha) methanotrophs, which are typical for acidic upland soils showing atmospheric methane oxidation. The methanotrophic community composition in lichen-dominated sites of a tundra wetland, therefore, was markedly different from that in bo- real Sphagnum peat bogs.