A novel anaerobic, mesophilic, slightly halophilic sulfate-reducing bacterium, designated strain Khaled BD4(T), was isolated from waters of a Tunisian thermal spring. Cells were vibrio-shaped or sigmoids (5-7×1-1.5 µm) and occurred singly or in pairs. Strain Khaled BD4(T) was Gram-stain-negative, motile and non-sporulated. It grew at 25-45 °C (optimum 37 °C), at pH 5.5-8.3 (optimum pH 7.0) and with 0.5-8% NaCl (optimum 3%). It required vitamins or yeast extract for growth. Sulfate, thiosulfate, sulfite and elemental sulfur served as terminal electron acceptors, but not fumarate, nitrate or nitrite. Strain Khaled BD4(T) utilized H2 in the presence of 2 mM acetate (carbon source), but also lactate, formate, pyruvate and fumarate in the presence of sulfate. Lactate was incompletely oxidized to acetate. Amongst substrates used, only pyruvate was fermented. Desulfoviridin and c-type cytochrome were present. The G+C content of the DNA was 54.6 mol%. The main fatty acids were anteiso -C(15 : 0), iso-C(18 : 0), iso-C(17 : 0) and iso-C(14 : 0). Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain Khaled BD4(T) had Desulfovibrio giganteus DSM 4123(T) (96.7% similarity) as its closest phylogenetic relative. On the basis of 16S rRNA gene sequence comparisons together with genetic and physiological characteristics, strain Khaled BD4(T) is assigned to a novel bacterial species, for which the name Desulfovibrio biadhensis sp. nov. is proposed. The type strain is Khaled BD4(T) ( = DSM 28904(T) = JCM 30146(T)).
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