Desulfobulbus oligotrophicus sp nov., a sulfate-reducing and propionate-oxidizing bacterium isolated from a municipal anaerobic sewage sludge digester

A novel, mesophilic, strictly anaerobic, sulfate-reducing and propionate-oxidizing bacterium, strain Prop6(T), was enriched and isolated from a municipal anaerobic sewage sludge digester. Cells were Gram-stain-negative, catalase-positive, oval rods, motile by means of amphitrichous flagella, non-spore-forming and contained menaquinone MK-5(H2) as the major respiratory quinone. The genomic DNA G+C content was 51.7 mol%. The optimal NaCl concentration, temperature and pH were 2-5 g l(-1), 35 degrees C and pH 7.6, respectively. Strain Prop6(T) could only oxidize propionate, lactate and pyruvate (weakly) with sulfate, sulfite or thiosulfate, mainly to acetate. Strain Prop6(T) fermented pyruvate and lactate to acetate and propionate. The predominant cellular fatty acids were C-14:0, C-16:0, C-16:1 omega 7, C-16 : 1 omega 5, C-17:1 omega 6 and C-18:1 omega 7. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the newly isolated strain was a member of the genus Desulfobulbus, with Desulfobulbus elongatus DSM 2908(T), Desulfobulbus propionicus DSM 2032(T) and Desulfobulbus rhabdoformis DSM 8777(T) as closest relatives among species with validly published names. On the basis of genotypic, phenotypic and chemotaxonomic characteristics, it is proposed that the isolate represents a novel species, Desulfobulbus oligotrophicus sp. nov. The type strain is Prop6(T) (=DSM 103420(T) =JCM 31535(T)).