Three sulfate-reducing bacterial strains designated SM40(T), SM41, and SM43 were isolated from marine sediment in the region of Skhira located in the Gulf of Gabes (Tunisia). These strains grew in anaerobic media with phosphogypsum as a sulfate source and sodium lactate as an electron and carbon source. One of them, strain SM40(T), was characterized by phenotypic and phylogenetic methods. Cells were ovoid, Gram-stain-negative and non-motile. The temperature limits for growth were 10 and 55 degrees C with an optimum at 35 degrees C and the pH range was 6.5-8.1 with an optimum at pH 7.5. Growth was observed at salinities ranging from 10 to 80 g NaCl l(-1) with an optimum at 30 g NaCl l(-1). Strain SM40(T) was able to utilize butanol, ethanol, formate, l-glucose, glycerol, lactate, propanol, propionate, and pyruvate as electron donors for the reduction of sulfate, sulfite, or thiosulfate to H2S. Without electron acceptors, strain SM40(T) fermented butanol and pyruvate. The DNA G+C content of strain SM40(T) was 52.6 mol %. Phylogenetic analysis based on the 16S rRNA gene sequence of the isolate revealed that strain SM40(T) was closely related to the species in the genus Desulfobulbus of the family Desulfobulbaceae. The sequence similarity between strain SM40 and Desulfobulbus marinus was 95.4%. The phylogenetic analysis, DNA G+C content, and differences in substrate utilization suggested that strain SM40 represents a new species of the genus Desulfobulbus, D. aggregans sp. nov. The type strain is strain SM40(T) (=DSM 28693(T) = JCM 19994(T)).