Thiovibrio frasassiensis gen. nov., sp. nov., an autotrophic, elemental sulfur disproportionating bacterium isolated from sulfidic karst sediment, and proposal of Thiovibrionaceae fam. nov.

A novel, autotrophic, mesophilic bacterium, strain RS19-109T, was isolated from sulfidic stream sediments in the Frasassi Caves, Italy. The cells of this strain grew chemolithoautotrophically under anaerobic conditions while disproportionating elemental sulfur (S0) and thiosulfate, but not sulfite with bicarbonate/CO2 as a carbon source. Autotrophic growth was also observed with molecular hydrogen as an electron donor, and S0, sulfate, thiosulfate, nitrate, and ferric iron as electron acceptors. Oxygen was not used as an electron acceptor and sulfide was not used as an electron donor. Weak growth was observed with sulfate as an electron acceptor and organic carbon as electron donors and carbon sources. The strain also showed weak growth by fermentation of tryptone. Strain RS19-109T was found to be phylogenetically distinct based on 16S rRNA gene sequence similarity (89.2%) to its closest relative, Desulfurivibrio alkaliphilus AHT2T. The draft genome sequence for strain RS19-109T had average nucleotide identity, average amino acid identity, and in silico DNA-DNA hybridization values of 72.2%, 63.0%, and 18.3%, respectively, compared with the genome sequence of D. alkaliphilus AHT2T. On the basis of its physiological and genomic properties, strain RS19-109T is proposed as the type strain of a novel species of a novel genus, Thiovibrio frasassiensis gen. nov., sp. nov. A novel family, Thiovibrionaceae fam. nov., is proposed to accommodate Thiovibrio within the order Desulfobulbales.