A novel moderately thermophilic and halophilic sulfate-reducing bacterium, strain TeSt(T), was isolated from production water of an oil field in Northern Germany near Hamburg. The cells were Gram-negative, straight to slightly curved rods and motile by a single polar flagellum. Only hydrogen and formate served as electron donors, whereas a wide variety of organic substrates and CO(2) could be used as carbon sources. Sulfate, sulfite, thiosulfate and sulfur were used as electron acceptors, but not nitrate or ferric iron. The novel isolate was negative for oxidase, catalase and desulfoviridin enzyme activity. Cytochromes were present and predominantly of the c-type. Whole-cells fatty acid patterns were dominated by the branched-chain fatty acids anteiso-C(15:0), iso-C(15:0), iso-C(17:0) and anteiso-C(17:0). As major respiratory lipoquinones partially saturated derivates of menaquinone 6 [MK-6(H(2)) and probably MK-6(H(4))] were identified. The G + C content of the genomic DNA was 41.3 mol% (HPLC method). An analysis of the 16S rRNA gene sequence indicated that strain TeSt(T) belongs to the family Desulfohalobiaceae within the class Deltaproteobacteria. The most closely related species with a sequence similarity of 95.0% was Desulfonauticus submarinus suggesting an affiliation of TeSt(T) to the genus Desulfonauticus. The novel isolate could be clearly distinguished from Desulfonauticus submarinus by its ability to grow chemolithoautotrophically and hence should be assigned to a novel species for which the name Desulfonauticus autotrophicus sp. nov. is proposed. The type strain is TeSt(T) (=DSM 4206(T)=JCM 13028(T)).