Thermodesulfovibrio autotrophicus sp. nov., the first autotrophic representative of the widespread sulfate-reducing genus Thermodesulfovibrio, and Thermodesulfovibrio obliviosus sp. nov. that has lost this ability

Representatives of the genus Thermodesulfovibrio are widespread thermophilic sulfate-reducing bacteria. The genus currently includes five species with validly published names. Two new Thermodesulfovibrio strains, 3907-1M ^T and 3462-1^T, were isolated with molecular hydrogen as an electron donor, sulfate as an electron acceptor and acetate as the carbon source from hot springs of Kunashir Island and Kamchatka Peninsula. Similar to other Thermodesulfovibrio species, the new isolates grew by reduction of sulfate, thiosulfate or Fe (III) with a limited range of electron donors, such as hydrogen (in the presence of acetate), formate (in the presence of acetate), pyruvate and lactate. Surprisingly, strain 3907-1M^T proved to be capable of autotrophic growth as well. Up to now, the genus Thermodesulfovibrio was represented by heterotrophic species only. Genome analysis revealed the presence of a gene cluster encoding enzymes of form III RubisCO-mediated transaldolase variant of the Calvin cycle in both strains, but genes encoding ribulose-1,5-bisphosphate carboxylase and phosphoribulokinase in the genome of the strain 3462-1^T contained internal stop codons in their sequences. On the basis of phylogenomic analysis, as well as distinct phenotypic and genomic properties, strain 3907-1M^T (=DSM 112797^T =JCM 39445^T =VKM B-3594^T =UQM 41601^T) is proposed to be classified as Thermodesulfovibrio autotrophicus sp. nov., and strain 3462-1^T (=JCM 39444^T =VKM B-3714^T =UQM 41602^T) – as Thermodesulfovibrio obliviosus sp. nov. Our results demonstrate a chemolithoautotrophic lifestyle in Thermodesulfovibrio representatives, suggesting greater ecological flexibility of this genus than previously assumed.