Isolation of a Novel Chemolithothrophic Sulfate-Reducing Firmicute from a Tyumen Thermal Borehole

— Hydrogen is a key energy-yielding substrate for microbial processes in the deep biosphere. Fracture water of a deep gold mine in South Africa is a well-known example of the ecosystem based on a hydrogenotrophic sulfate reducer, “ Candidatus Desulforudis audaxviator.” The present work reports the cultivation and pure culture isolation of a novel obligate chemolithotroph reducing sulfate during growth on hydrogen or formate. Phylogenetic analysis of the 16S rRNA gene of the strain Tu-874 showed its clusterization with its closest cultured relative, “ Candidatus Desulforudis audaxviator.” However, the low 16S rRNA sequence similarity of 88.95% indicates that the organism represents a new taxonomic group above the species level.