A novel thermophilic, anaerobic, chemolithoautotrophic bacterium, strain SF97T, was isolated from a terrestrial hot spring (Kuril Islands, Russia). Cells of strain SF97T were rod-shaped and motile with a Gram-positive cell-wall type. The novel isolate grew at 45-72 °C (optimum 65 °C) and pH 5.5-8.5 (optimum 6.0-6.5). The strain grew chemolithoautotrophically with molecular hydrogen as an electron donor, sodium sulfite or SO2 gas as an electron acceptor and bicarbonate/CO2 as a carbon source. Sulfate, thiosulfate, elemental sulfur, Fe(III) or nitrate were not used as electron acceptors either with H2 or organic electron donors. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the isolate belonged to the family Thermoanaerobacteraceae, order Thermoanaerobacterales, and was distantly related to species of the genus Ammonifex (92-93 % sequence similarity). On the basis of its physiological properties and results of phylogenetic analyses, strain SF97T is considered to represent a novel species of a new genus, for which the name Thermodesulfitimonas autotrophica gen. nov., sp. nov. is proposed. The type strain of Thermodesulfitimonas autotrophica is SF97T (=DSM 102936T=VKM B-2961T). T. autotrophica is the first reported obligate sulfite-reducing micro-organism.