Several strains of sulfate-reducing bacteria were isolated from marine sediments recovered near Tunis, Korbous and Bizerte, Tunisia. They all showed characteristics consistent with members of the genus Desulfovibrio. One of these strains, designated MB3(T), was characterized further. Cells of strain MB3(T) were slender, curved, vibrio-shaped, motile, Gram-negative, non-spore-forming rods. They were positive for desulfoviridin as bisulfite reductase. Strain MB3(T) grew at temperatures of 15-45 degrees C (optimum 40 degrees C) and at pH 6.0-8.1 (optimum pH 7.0). NaCl was required for growth (optimum 20 g NaCl l(-1)). Strain MB3(T) utilized H(2) in the presence of acetate with sulfate as electron acceptor. It also utilized lactate, ethanol, pyruvate, malate, fumarate, succinate, butanol and propanol as electron donors. Lactate was oxidized incompletely to acetate. Strain MB3(T) fermented pyruvate and fumarate (poorly). Electron acceptors utilized included sulfate, sulfite, thiosulfate, elemental sulfur and fumarate, but not nitrate or nitrite. The G+C content of the genomic DNA was 51 mol%. On the basis of genotypic, phenotypic and phylogenetic characteristics, strain MB3(T) (=DSM 18034(T)=NCIMB 14199(T)) is proposed as the type strain of a novel species, Desulfovibrio bizertensis sp. nov.