Insight into the role of bacteria in degradation of diatoms is important for understanding the factors and components of silica turnover in aquatic ecosystems. Using microscopic methods, it has been shown that the degree of diatom preservation and the numbers of diatom-associated bacteria in the surface layer of bottom sediments decrease with depth; in the near-bottom water layer, the majority of bacteria are associated with diatom cells, being located either on the cell surface or within the cell. The structure of microbial community in the near-bottom water layer has been characterized by pyrosequencing of the 16S rRNA gene, which has revealed 149 208 unique sequences. According to the results of metagenomic analysis, the community is dominated by representatives of Proteobacteria (41.9%), Actinobacteria (16%); then follow Acidobacteria (6.9%), Cyanobacteria (5%), Bacteroidetes (4.7%), Firmicutes (2.8%), Nitrospira (1.6%), and Verrucomicrobia (1%); other phylotypes account for less than 1% each. For 18.7% of the sequences, taxonomic identification has been possible only to the Bacteria domain level. Many bacteria identified to the genus level have close relatives occurring in other aquatic ecosystems and soils. The metagenome of the bacterial community from the near-bottom water layer also contains 16S rRNA gene sequences found in previously isolated bacterial strains possessing hydrolytic enzyme activity. These data show that potential degraders of diatoms occur among the vast variety of microorganisms in the near-bottom water of Lake Baikal.

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BackgroundRhodococci are bacteria able to degrade a wide range of hydrocarbons, including the alkanes present in crude oil, due to alk genes in their genomes.FindingsGenome sequencing of DNA from Rhodococcus erythropolis strain 4 (obtained from a deep-water bitumen mound) revealed four alk genes, and the predicted amino acid sequences coded by these genes were highly conserved, having sections up to 11 amino acid residues.ConclusionsObtained four genes from Rhodococcus erythropolis were similar to corresponding genes from other bacteria collected from other environments, including marine sources. This indicated a large-scale horizontal alk gene transfer between bacteria from different subgenera.