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A novel weakly halotolerant, sulfate-reducing bacterium, designated strain RB22T, was isolated from exhaust water of a Tunisian oil refinery. Cells of strain RB22T were Gram-negative, motile, vibrio-shaped or sigmoid and non-spore-forming, and occurred singly or in chains. Strain RB22T grew between 15 and 45 °C (optimum, 37 °C) and at pH 4.5 to 9 (optimum, pH 7). NaCl was not required for growth, but the strain tolerated high NaCl concentrations (up to 70 g l−1) with an optimum of 40 g l−1. Sulfate, thiosulfate, sulfite and elemental sulfur served as electron acceptors, but not fumarate. Nitrate and nitrite were not reduced. Strain RB22T utilized lactate, formate, fumarate, succinate, glycerol, H2+CO2 and methanol as substrates. The DNA G+C content was found to be 59.6 mol%. Phylogenetic analysis based on the 16S rRNA gene revealed that the isolate was a member of the genus Desulfovibrio, with no close relatives at the species level (16S rRNA gene sequence similarity of less than 95 %). Strain RB22T exhibited levels of 16S rRNA gene sequence similarity of 94.6 and 94.12 % to the type strains of the closely related species Desulfovibrio aespoeensis and Desulfovibrio dechloracetivorans, respectively. On the basis of genotypic and phylogenetic characteristics, and significant phenotypic differences, we suggest that strain RB22T represents a novel species, for which the name Desulfovibrio tunisiensis sp. nov. is proposed. The type strain is RB22T (=NCIMB 14400T=JCM 15076T=DSM 19275T).
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