Complete Genome Sequence of an Uncultured Bacterium of the Candidate Phylum Bipolaricaulota

Bacteria of the candidate phylum Bipolaricaulota, previously known as OP1 and Acetothermia, have been identified in various terrestrial and marine ecosystems as a result of molecular analysis of microbial communities. To date, none of the members of Bipolaricaulota has been isolated in a pure culture. We assembled the complete closed genome sequence of the bacterium of this phylum from the metagenome of a subsurface thermal aquifer and used the genomic data to analyze the phylogenetic position and metabolic potential of this bacterium. Analysis of the genome of this bacterium, designated Ch78, revealed various transporters of sugars and peptides and limited capacities for the extracellular hydrolysis of polysaccharides. Reconstruction of the central metabolic pathways suggested that the bacterium Ch78 is an anaerobic organotroph capable of fermenting sugars and proteinaceous substrates. Known pathways of aerobic and anaerobic respiration, as well as of autotrophic carbon fixation, were not found in the Ch78 genome. In the subsurface aquifer Bipolaricaulota probably consume low-molecular weight organic compounds and produce hydrogen and acetate. Based on the results of phylogenetic and genomic analysis, classification of the novel bacterium as "Candidatus Bipolaricaulis sibiricus" is proposed.