Bacterial communities of the Selenga River, its tributaries and Selenginskoe shallow water in the summer period of 2021

The first data on the diversity and structure of bacterial communities in the Selenga River, its tributaries and delta waters (Selenga shallow water) during the summer high-water period of 2021 were obtained. A tendency towards a gradual decrease in chemical indicators (alkalinity, mineralization, concentrations of sulfate and chloride ions) was revealed downstream in the Russian part of the Selenga River. As before, the chemical composition of the Selenga River waters was determined by water content and anthropogenic load, while the influence of tributary waters was local. At a distance of 1 km from the mouths in the mixing zone of river water and lake water, the chemical composition and taxonomic structure of bacterial communities were close to those observed in the pelagic zone of Lake Baikal. In all analyzed 16S rRNA gene libraries, 9 common bacterial phyla were identified, with a predominance of Pseudomonadota (51.71–76.83%) in river communities and Actinomycetota (17.28–66.32%) in the communities of the Selenga shallows. The most significant differences in the taxonomic composition of bacterial communities were noted at the genus level. It is assumed that there is a stable bacterial community throughout the Selenga River, the main representatives of which are bacteria of the Limnohabitans, Pseudarcicella, Rhodoluna, and Polynucleobacter genera, which also dominate in the small rivers of Southern Baikal. Comparative analysis of the diversity of tributary communities did not reveal a significant impact on the microbiomes of the Selenga River and Lake Baikal: only a few river bacterial taxa were identified in the littoral and pelagic zones of the lake.