A novel sulfur-reducing bacterium, strain K6013(T), was isolated from a sulfide sample collected at a depth of 2771 m from a high-temperature hydrothermal vent in the Indian Ocean. Cells were Gram-stain-negative, anaerobic, motile rods (0.92.2 x 0.4-0.6 mu m). The strain grew at NaCl concentrations ranging from 1 to 4.5% (w/v) (optimum 2.5 %), at pH 5 to 8 (optimum pH 6), and at temperatures between 40 and 75 degrees C (optimum 65 degrees C). K6013(T) was an obligate chemolithoautotroph, using thiosulfate, sulfur and nitrate as terminal electron acceptors in the presence of H-2 but not sulfate, sulfite nor nitrite. The major cellular fatty acids were C-16 : 0 (17.4 %), C-18 : 1 omega 7c/C-18 : 1 omega 6c (ummed feature 8, 37.91 %), C-18 : 0 (18.29 %) and C-14 : 0 3-OH/iso-C-16: I-1 (summed feature 2, 8.56 %). The DNA G+C content was 38.2 mol%. The results of phylogenetic 16S rRNA gene sequence analyses indicated that K6013(T) represents a member of the genus Desulfurobacterium within the class Aquificae, with highest sequence similarity of 96.93% to Desulfurobacterium atlanticum SL22(T). On the basis of genotypic and phenotypic data, K6013(T) is considered to represent a novel species of the genus Desulfurobacterium, for which the name Desulfurobacterium indicum sp. nov. is proposed, with the type strain K6013(T) (=DSM 101677(T)=MCCC 1A01868(T)).