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

A novel, autotrophic, mesophilic bacterium, strain RS19-109^T, was isolated from sulphidic stream sediments in the Frasassi Caves, Italy. The cells of this strain grew chemolithoautotrophically under anaerobic conditions while disproportionating elemental sulphur (S⁰) and thiosulphate, but not sulphite with bicarbonate/CO₂ as a carbon source. Autotrophic growth was also observed with molecular hydrogen as an electron donor, and S⁰, sulphate, thiosulphate, nitrate and ferric iron as electron acceptors. Oxygen was not used as an electron acceptor and sulphide was not used as an electron donor. Weak growth was observed with sulphate as an electron acceptor and organic carbon as an electron donor and carbon source. The strain also showed weak growth by fermentation of tryptone. It grew at pH 5.5–7.5 (optimum, pH 7.0), 4–35 °C (optimum, 30 °C) and between 0–1.7 % NaCl. Strain RS19-109^T was found to be phylogenetically distinct based on 16S rRNA gene sequence similarity (89.2 %) to its closest relative, Desulfurivibrio alkaliphilus AHT2^T. The draft genome sequence for strain RS19-109^T 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 AHT2^T. On the basis of its physiological and genomic properties, strain RS19-109^T 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 . Strain RS19-109^T has been deposited at the DSMZ-German Collection of Microorganisms and Cell Cultures (=DSM 115074^T) and the American Type Culture Collection (=ATCC TSD-325^T).