A new moderately halophilic sulfate-reducing bacterium (strain H (1) (T) ) was enriched and isolated from a wastewater digestor in Tunisia. Cells were curved, motile rods (2-3 x 0.5 mu m). Strain H (1) (T) grew at temperatures between 22 and 43A degrees C (optimum 35A degrees C), and at pH between 5.0 and 9.2 (optimum 7.3-7.5). Strain H (1) (T) required salt for growth (1-45 g of NaCl/l), with an optimum at 20-30 g/l. Sulfate, sulfite, thiosulfate, and elemental sulfur were used as terminal electron acceptors but not nitrate and nitrite. Strain H (1) (T) utilized lactate, pyruvate, succinate, fumarate, ethanol, and hydrogen (in the presence of acetate and CO2) as electron donors in the presence of sulfate as electron acceptor. The main end-products from lactate oxidation were acetate with H-2 and CO2. The G + C content of the genomic DNA was 55%. The predominant fatty acids of strain H (1) (T) were C-15:0 iso (38.8%), C-16:0 (19%), and C-14:0 iso 3OH (12.2%), and menaquinone MK-6 was the major respiratory quinone. Phylogenetic analysis of the small-subunit (SSU) ribosomal RNA (rRNA) gene sequence indicated that strain H (1) (T) was affiliated to the genus Desulfovibrio. On the basis of SSU rRNA gene sequence comparisons and physiological characteristics, strain H (1) (T) is proposed to be assigned to a novel species of sulfate reducers of the genus Desulfovibrio, Desulfovibrio legallis sp. nov. (= DSM 19129(T) = CCUG 54389(T)).