Striking differences in the microbial community in sediments of a longitudinal subdivided drinking water reservoir system

Sediments contain a huge number and diversity of microorganisms that are important for the flux of material and are pivotal to all major biogeochemical cycles. Sediments of reservoirs are affected by a wide spectrum and degree of allochthonus and autochthonus influences providing versatile environments along the flow of water within the reservoir. Here we report on the microbial diversity in sediments of the mesotrophic drinking water reservoir Saidenbach, Germany, featuring a pronounced longitudinal gradient in sediment composition in the reservoir system. Three sampling sites were selected along the gradient, and the microbial communities in two sediment depths were characterized using catalysed reporter deposition fluorescence in situ hybridization (CARD-FISH) and a bar-coded pyrosequencing approach. Multivariate statistics was used to reveal relationships between sequence diversity and the environmental conditions. The microbial communities were incredibly diverse with a Shannon index of diversity (H’) ranging from 7.29 to 7.53. 17,751 sequences could be classified into 21 phyla, but the full extent of genetic diversity was not captured. CARD-FISH gave a overview about the community composition; more detailed information was gained by pyrosequencing. Bacteria were more abundant than Archaea. The dominating phylum in all samples was Proteobacteria, especially Betaproteobacteria and Deltaproteobacteria. Furthermore, sequences of Bacteroidetes, Verrucomicrobia, Acidobacteria, Chlorobi, Nitrospirae, Alphaproteobacteria, Gammaproteobacteria and Chloroflexi were found. Significant differences in the community composition between most samples were detected. A significant correlation between the site water content and the microbial community composition was observed, but also dissolved manganese, temperature and nitrate concentration revealed feasible predictive power.