Microbial Diversity of the Baikal Rift Zone Freshwater Alkaline Hot Springs and the Ecology of Polyextremophilic Dissimilatory Iron-Reducing Bacteria

Polyextremophilic microbial communities of Baikal Rift Zone hot springs have been studied fragmentarily, and these studies have typically focused on either phototrophic microbial mats or on the whole microbial community from one or a few sites. In our work, we conducted the first large-scale screening of microbial communities from seven hot spring groups in the Baikal Rift Zone, using metabarcoding of the V3-V4 regions of the 16S rRNA gene. Analysis of alpha and beta diversity, as well as co-occurrence network analysis, revealed that the microbial diversity of the studied springs is highly dependent on temperature values. This approach allowed classifying microbial communities into four distinct groups, characterized by significantly different taxa representing the key functional roles of primary producers, heterotrophic consumers, and terminal destructors of organic matter. Sulfate-reducing bacteria constituted a major metabolic group driving the final stage of organic matter mineralization. Moreover, the presence of alkalithermophilic dissimilatory iron reducers, whose existence was debatable, was proved in the studied samples by cultural methods. The phylotypes that gained an advantage on selective media with synthesized ferrihydrite and hydrogen or acetate added as an electron donor belonged to the genus <i>Parvivirga</i> of the order <i>Anaerosomatales</i> and several unknown representatives of the phylum <i>Bacillota</i>.