Recently, presence of sulfur-disproportionating bacterial species belonging to the phylum Nitrospirota was indicated by an enrichment culture-based study. In the present study, a strain representing that species was isolated and characterized. The strain, strain T55JT, was isolated from a microbial mat of a hot spring. The cells were motile, and rods or spiral forms with width of 0.32-0.49 μm. The strain grew autotrophically, only by disproportionation of thiosulfate or elemental sulfur. Growth was observed at a temperature range of 25-60°C, with optimum growth at 53-57°C. The pH range for growth was 5.5-9.0, with optimum pH of 7.0-8.0. The complete genome of strain T55JT is composed of a circular chromosome (2,370,875 bp), with G+C content of 38.7%. Thermodesulfovibrio hydrogeniphilus Hdr5T showed the highest sequence similarity of the 16S rRNA gene to strain T55JT, but it was only 88.2%. On the basis of the phylogenetic and physiologic properties, strain T55JT (= DSM 110365T=NBRC 114245T) is proposed as type strain of a novel species in a new genus, Dissulfurispira thermophila gen. nov., sp. nov. To assign the new genus to family and higher taxa, its taxonomic position was assessed by genome-based phylogeny. As a result, it was shown that the novel genus and Thermodesulfovibrio belong to different families. It was also shown that Thermodesulfovibrio should be reclassified at levels from class to family and creation of some novel taxa is required. Based on these results, Thermodesulfovibrionia class. nov., Thermodesulfovibrionales ord. nov., Thermodesulfovibrionaceae fam. nov., and Dissulfurispiraceae fam. nov. are proposed.
Keywords: Nitrospirota; Novel genus; Strict anaerobe; Sulfur disproportionation; Thermodesulfovibrio; Thermophile.
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