Desulfobulbus japonicus sp nov., a novel Gram-negative propionate-oxidizing, sulfate-reducing bacterium isolated from an estuarine sediment in Japan

Two strictly anaerobic, mesophilic, sulfate-reducing bacterial strains, Pro1(T) and Pro16, were isolated from an estuarine sediment in the Sea of Japan of the Japanese islands and were characterized by phenotypic and phylogenetic methods. Strains Pro1(T) and Pro16 had almost the same physiological and chemotaxonomic characteristics. Cells of both strains were Gram-negative, motile, non-spore-forming rods. Catalase activity was not detected. The optimum NaCl concentration for growth was 3.0 % (w/v). The optimum temperature for growth was 35 degrees C and the optimum pH was 6.7. Both strains used formate, propionate, pyruvate, lactate, fumarate, malate, ethanol, propanol, butanol, glycerol, alanine, glucose, fructose and H-2 as electron donors for sulfate reduction and did not use acetate, butyrate, succinate, methanol, glycine, serine, aspartate, glutamate, cellobiose or sucrose. Organic electron donors were incompletely oxidized mainly to acetate. Both strains also used thiosulfate as an electron acceptor. Without electron acceptors, both strains fermented pyruvate and lactate. The genomic DNA G + C contents of strains Pro1(T) and Pro16 were 48.6 and 46.0 mol%, respectively. The major respiratory quinone of both strains was menaquinone MK-5(H-2). Major cellular fatty acids of both strains were C-15:0 C-16:0, C-17:1 omega 6 and C(18:1)w7. Phylogenetic analysis based on 16S rRNA gene sequences placed both strains in the class Deltaproteobacteria. The closest recognized relative of strains Pro1(T) and Pro16 was Desulobulbus mediterraneus with sequence similarities of 95.2 and 94.8 %, respectively. Based on phylogenetic, physiological and chemotaxonomic characteristics, strains Pro1(T) and Pro16 represent a novel species of the genus Desulfobulbus, for which the name Desulobulbus japonicus is proposed. The type strain is Pro1(T)(=JCM 14043(T) =DSM 18378(T)) and strain Pro16 (=JCM 14044 DSM 18379) is a reference strain.