Abstract—A total of 170 heterotrophic bacterial strains were isolated from Lake Baikal epilithic biofilms. Identification of the isolates was carried out using the 16S rRNA gene sequencing and physiological and biochemical characteristics. Phylogenetic analysis revealed 59 phylotypes, with three strains probably belonging to new prokaryotic taxa. Members of the cultured biofilm community belonged to 4 phyla and 32 bacterial genera: Proteobacteria (51%), Firmicutes (30%), Actinobacteria (15%), and Bacteroidetes (4%). The genera Aeromonas, Pseudomonas, and Bacillus were predominant. Diversity of the cultured microbial community was higher in the epilithic biofilms than in the water column, neuston, and sponges. Among the isolates, members of ten genera have not been previously found in the Lake Baikal ecosystem: Actinobacteria (Microcella, Pseudoclavibacter, Glaciihabitans, Plantibacter, and Sanguibacter), Proteobacteria (Devosia, Roseomonas, Hydrogenophaga, Iodobacter, and Rhizobium); Glaciihabitans spp. ВА-51-09, ВА-73-09 and Rhizobium sp. ВА-57-09 were new prokaryotic taxa. Statistically significant differences were revealed in the frequency of occurrence of the strains isolated from biofoulings on a steel plate and on natural substrates, as well as on nutrient media with different composition of organic compounds. Most isolates of the genera Aeromonas, Pseudomonas, and Bacillus were capable of degradation of six different polymer substrates, which may indicate their active involvement in organic matter decomposition in biofilms and in Lake Baikal ecosystem in general.