Taxonomic diversity and metabolic activity of microbial communities in rivers and estuarine waters of Southern Baikal in summer

We analyzed the diversity of bacterial communities, metabolic activity, pH, and anthropogenic impact in the water of the estuaries and estuarine waters of the rivers in Southern Baikal in 2018 with different chemical composition. The chemical composition of waters and values of total microbial count (TMC), organotrophic bacteria (OB), and bacterial production (BP) depended on the geographical position, length of the rivers, and their water quality. In rivers with water acidification, we did not detect an effect of pH on TMC, abundance of OB, or total amount of mesophilic aerobic and facultative anaerobic microorganisms (PC). In rivers with a discharge of untreated domestic sewage, there was an increase in the content of dissolved organic carbon (DOC), concentration of nutrients, number of fecal and mesophilic bacteria, and high metabolic activity of microorganisms. The value of bacterioplankton production reached 0.26 to 12.41 per day^?1; TMC – 0.155 ± 0.002 to 3.474 ± 0.044 million cells/mL. Using the massive parallel sequencing of fragments encoding the V2–V3 region of the 16S rRNA gene, we studied the diversity of bacteria and estimated the influence of chemical composition on the diversity of communities. As in other freshwater ecosystems and the pelagic zone of Lake Baikal, the members of freshwater Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, and Verrucomicrobia predominated in the estuaries and estuarine waters of the rivers. The obtained data on the number and diversity of hygiene indicator bacteria suggested fecal pollution of the rivers of Southern Baikal.