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)).