Bacteroides propionicifaciens sp nov., isolated from rice-straw residue in a methanogenic reactor treating waste from cattle farms

Two strictly anaerobic bacterial strains (SV434(T) and S562) were isolated from rice-straw residue in a methanogenic reactor treating waste from cattle farms in Japan. They had identical 16S rRNA gene sequences and showed almost the same phenotypic properties. The cells of both strains were Gram-negative, non-motile, non-spore-forming rods; extraordinarily long rods often occurred. Remarkable stimulation of growth occurred with the addition of haemin and cobalamin (vitamin B-12) to the medium. The supplementary cobalamin and haemin could be replaced if autoclaved and clarified sludge fluid obtained from the reactor was added. Both strains utilized a range of growth substrates, including arabinose, fructose, galactose, glucose, mannose, cellobiose, maltose, glycogen, starch, dextrin, amygdalin, lactate and pyruvate. Both strains produced acetate and propionate with a small amount of succinate from these substrates in the presence of haemin and cobalamin. Both strains were slightly alkaliphilic, having a pH optimum at about 7.9. The temperature range for growth was 5-35 degrees C, the optimum being 30 degrees C. The NaCl concentration range for growth was 0-4% (w/v). Catalase activity was not detected in cells cultivated without haemin, whereas cells cultivated with haemin usually had the enzyme activity. Oxidase and nitrate-reducing activities were not detected. Aesculin was hydrolysed, but gelatin was not hydrolysed. Both strains were sensitive to bile acids. The major cellular fatty acids of both strains were anteiso-C-15:0 and iSo-C-15:0. Menaquinones MK-8(H-0) and MK-9(H-0) were the major respiratory quinones and the genomic DNA G + C contents were 46.2-47.5 mol%. A phylogenetic analysis based on 16S rRNA gene sequences placed both strains in the phylum Bacteroidetes. Bacteroides coprosuis (isolated from swine-manure storage pits) was the species most closely related to both strains (95.9% 16S rRNA gene sequence similarity to the type strain). On the basis of the phylogenetic, physiological and chemotaxonomic analyses, strains SV434(T) and S562 represent a novel species of the genus Bacteroides, for which the name Bacteroides propionicifaciens sp. nov. is proposed. The type strain is SV434(T) (=jCM 14649(T) =DSM 19291(T)).