Structure of Bacterial Communities in the Area Where the Selenga River Flows into Lake Baikal during the Ice Period

The chemical composition and structure of bacterial communities at the mouths of two channels of the Selenga River delta and its delta water area (Selenga shallow water) were studied during the ice season of 2021. The highest concentrations of the main ions and biogenic elements were found in the channels: their values exceeded those in the delta water area by >7 times. A high number of organotrophic, oligotrophic, psychrotolerant, and sanitary-significant bacteria were determined at the mouths. As the river water mixed with the lake water, as near as 1 km from the mouths, changes were recorded in the chemical composition, the number of studied groups of microorganisms, the taxonomic structure of bacterial communities, and their correlation with physicochemical conditions were observed. Seven common bacterial phyla were identified in the studied communities: Actinobacteriota, Bacteroidota, Chloroflexi, Cyanobacteria, Patescibacteria, Proteobacteria, and Verrucomicrobiota. The bacteria predominating at the mouths of the channels were Campylobacterota, Bacteroidota, Actinobacteriota and Gammaproteobacteria, involved in the sulfur and nitrogen cycles. In the Selenga shallows, representatives of Alphaproteobacteria, Cyanobacteria, Verrucomicrobiota and Actinobacteriota, characteristic of the pelagic zone of Lake Baikal, dominated. The authors suggest that the microorganisms of the Selenga River have a local impact on the microbiome of Baikal, only some of them are able to function in both the littoral and pelagic zones of the lake.