A novel, moderately thermophilic, chemo-organotrophic bacterium was isolated from formation fluid samples from an offshore oil-production well head at Bombay High (Western India). Cells were rod-shaped with a sheath-like outer structure ('toga'); the cells appeared singly, in pairs or in short chains. Cells grew at 25-70 6C (optimum 55-58 6C), pH 5.5-9.0 (optimum pH 7.3-7.8) and 0-12 % (w/v) NaCl (optimum 4.0-4.5 %). The isolate was able to grow on various carbohydrates or complex proteinaceous substances. The isolate reduced thiosulfate and elemental sulfur. The major end products of glucose fermentation were acetate, H 2 and CO 2 . The DNA G+C content of the genomic DNA was 26.8 mol%. Phylogenetic analysis of the 16S rRNA gene placed the strain within the order Thermotogales in the bacterial domain. On the basis of 16S rRNA gene sequence comparisons and in combination with morphological and physiological characteristics, the isolate represents a novel species of new genus, for which the name Oceanotoga teriensis gen. nov., sp. nov. is proposed. The type strain of the type species is OCT74 T (5JCM 15580Petroleum reservoirs constitute a group of unique sites with respect to their physico-chemical conditions (halophilic and thermophilic) and provide ecological niches from which taxonomically, physiologically and phylogenetically unusual microbes can be isolated (Bhupathiraju et al., 1993;Ravot et al., 1995;Fardeau et al., 1997). Members of the order Thermotogales, first described as an order containing hyperthermophilic bacteria, have been isolated from extreme environments such as deep-sea hydrothermal vents, hot springs, continental and subcontinental volcanic areas, marine sediments and oil reservoirs (Nunoura et al., 2007; Alain et al., 2002;Huber & Stetter, 1992;Davey et al., 1993).Within the order Thermotogales, the genera Thermotoga Feng et al., 2010) have been described. Representatives of these genera are anaerobic, chemo-organotrophic, thermophilic, Gram-negative, non-sporulating, rod-shaped bacteria that are characterized by a sheath-like outer structure called the 'toga ' (Huber et al., 1986). In this study, a novel strain of moderately thermophilic bacteria is described that was isolated from offshore oil-producing well heads located at Bombay High (Western India).Formation fluid samples were collected from oil-well heads into 50 ml anaerobic sterilized serum bottles containing sodium sulfide at a final concentration of 20 mM. Samples were transported to the laboratory under ambient conditions. Collection of samples was performed from December 2007 to January 2008.A basal medium composed of (l 21 deionized water): 1 g NH 4 Cl 2 , 0.3 g K 2 HPO 4 , 0.3 g KH 2 PO 4 , 0.2 g MgCl 2 . 6H 2 O, 0.1 g CaCl 2 . 2H 2 O, 10.0 g NaCl, 0.1 g KCl, 0.5 g NaC 2 H 3 O 2 , 2.0 g yeast extract, 2.0 g bio-Trypticase, 1 mg resazurin and 10.0 ml trace mineral element solution (Balch et al., 1979) was used for isolation and routine cultivation. The pH of the medium was adjusted to 7.5 with 1 M KOH at ambient temperature b...