Effects of salinity and nutrients on sedimentary bacterial communities in oligosaline Lake Bosten, northwestern China

Lake Bosten, a large oligosaline lake in arid northwestern China, has evolved from a freshwater lake and is influenced by eutrophication processes. Since sediments record past limnic changes, the analysis of sedimentary bacteria in Lake Bosten may help elucidate bacterial responses to both salinization and eutrophication. We characterized the intrasystem distribution of sedimentary bacterial communities between freshwater and oligosaline regions of Lake Bosten using denaturing gradient gel electrophoresis and 16S rRNA gene clone libraries. Both principal component analysis and redundancy analysis revealed that salinity was the dominant and pronounced intrasystem factor that shaped the sedimentary bacterial community composition in Lake Bosten. In total, 349 clones and 185 distinct operational taxonomic units were acquired from 4 clone libraries. Proteobacteria (41.5%) was the most abundant phylum, followed by Bacteroidetes (13.5%), Chloroflexi (8.9%), Firmicutes (8.6%) and others. The higher bacterial diversities and proportions of Beta-and Deltaproteobacteria in the oligosaline regions than in the freshwater region reflected the responses of sedimentary bacteria to increased salinity and nutrient levels. The scarceness of typical freshwater bacteria, the relatively high percentage (12.3% of total bacteria) of putative sulfate-reducing bacteria and a high percentage of unclassified bacteria in the sediments all highlight the uniqueness of sedimentary bacterial communities in the early stages of salinization and eutrophication.