Metagenomic analyses on microbial assemblages of Lake Soyang, a temperate monomictic reservoir

초록

It is important to understand structure and function of microbial communities of inland waters, since inland waters play significant roles in global biogeochemical cycling and microbial assemblages are crucial for most biogeochemical processes. In this study, to expand the understanding of the microbial community of freshwater environments, we performed metagenome sequencing of water column microbial communities of Lake Soyang, the largest reservoir in South Korea. Eight water samples were collected from two depths (1 m and 50 m) for four seasons. Metagenome sequencing was performed for DNA samples extracted from microbial size fraction (0.2?3.0 μm), yielding >10 Gbp for each sample. Taxonomic profiling of metagenome showed that bacterial communities of Lake Soyang were largely dominated by Actinobacteria (such as the acI lineage) and Alphaproteobacteria (such as the LD12 clade) and were more variable at 1 m than at 50 m, which were consistent with the results from amplicon sequencing of 16S rRNA genes. Through metagenome assembly and contig binning, we were able to obtain >200 metagenome-assembled genomes (MAGs). The MAGs were mainly affiliated with Actinobacteria, Betaproteobacteria, and Bacteroidetes. A large number of MAGs belonging to diverse tribes of the acI lineage were also retrieved. In fragment recruitment analysis, the acI MAGs of diverse tribes showed distinct distribution patterns depending on season and depth. These results would contribute to understanding of global freshwater microbial diversity. Analyses on the samples collected more thoroughly (from 5 depths during 2 years) are in progress.