A Novel View on the Taxonomy of Sulfate-Reducing Bacterium ' Desulfotomaculum salinum ' and a Description of a New Species Desulfofundulus salinus sp. nov.

Two thermophilic spore-forming sulfate-reducing strains, 435 T and 781, were isolated from oil and gas reservoirs in Western Siberia (Russia) about 50 years ago. Both strains were found to be neutrophilic, chemoorganotrophic, anaerobic bacteria, growing at 45-70 °C (optimum, 55-60 °C) and with 0-4.5% ( w / v ) NaCl (optimum, 0.5-1% NaCl). The major fatty acids were iso-C 15:0 , iso-C 17:0 , C 16:0 , and C 18:0 . In sulfate-reducing conditions, the strains utilized H 2 /CO 2 , formate, lactate, pyruvate, malate, fumarate, succinate, methanol, ethanol, propanol, butanol, butyrate, valerate, and palmitate. In 2005, based on phenotypic characteristics and a 16S rRNA gene sequence analysis, the strains were described as ' Desulfotomaculum salinum ' sp. nov. However, this species was not validly published because the type strain was not deposited in two culture collections. In this study, a genomic analysis of strain 435 T was carried out to determine its taxonomic affiliation. The genome size of strain 435 T was 2.886 Mb with a 55.1% genomic G + C content. The average nucleotide identity and digital DNA-DNA hybridization values were highest between strain 435 T and members of the genus Desulfofundulus , 78.7-93.3% and 25.0-52.2%, respectively; these values were below the species delineation cut-offs (<95-96% and <70%). The cumulative phenotypic and phylogenetic data indicate that two strains represent a novel species within the genus Desulfofundulus , for which the name Desulfofundulus salinus sp. nov. is proposed. The type strain is 435 T (=VKM B-1492 T = DSM 23196 T ). A genome analysis of strain 435 T revealed the genes for dissimilatory sulfate reduction, autotrophic carbon fixation via the Wood-Ljungdahl pathway, hydrogen utilization, methanol and organic acids metabolism, and sporulation, which were confirmed by cultivation studies.