Xylanibacter oryzae gen. nov., sp. nov., a novel strictly anaerobic, Gram-negative, xylanolytic bacterium isolated from rice-plant residue in flooded rice-field soil in Japan.

A strictly anaerobic, xylanolytic bacterium, strain KB3(T), isolated from rice-plant residue in flooded anoxic rice-field soil in Japan, was characterized phenotypically and phylogenetically. Cells were Gram-negative, non-motile, non-spore-forming, short to filamentous rods. Growth of the strain was remarkably stimulated by the addition of haemin to the medium. The novel strain utilized various sugars including xylan, xylose, pectin and carboxymethylcellulose and produced acetate, propionate and succinate with a small amount of malate. Propionate production was stimulated by the addition of a B-vitamin mixture or cobalamin to the medium. The novel strain was slightly acidophilic with an optimum pH 5.7-6.2 and the optimum growth temperature was 30 degrees C. Oxidase, catalase and nitrate-reducing activities were negative. Aesculin was hydrolysed. The major cellular fatty acids were anteiso-C(15 : 0) and iso-3-OH C(17 : 0). The major respiratory quinones were menaquinones MK-12(H(2)) and MK-13(H(2)). The genomic DNA G+C content was 43.6 mol%. Phylogenetic analysis based on 16S rRNA gene sequence placed the strain in the phylum Bacteroidetes. The closest related species was Prevotella bivia with a 16S rRNA gene sequence similarity of 89.5 %. Prevotella albensis and Prevotella oulorum were the next closest recognized species with sequence similarities of 89.1 %. Based on a comprehensive examination of the differences in phylogenetic, ecological, physiological and chemotaxonomic characteristics of strain KB3(T) and those of related species, a novel genus and species, Xylanibacter oryzae gen. nov., sp. nov., is proposed to accommodate strain KB3(T). The type strain of the novel species is KB3(T) (=JCM 13648(T)=DSM 17970(T)).