Three sulfate-reducing bacterial strains designated SM40T, 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 SM40T, 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 °C with an optimum at 35 °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 SM40T 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 SM40T fermented butanol and pyruvate. The DNA G+C content of strain SM40T was 52.6 mol %. Phylogenetic analysis based on the 16S rRNA gene sequence of the isolate revealed that strain SM40T 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 SM40T (=DSM 28693T = JCM 19994T).