Paludibacter propionicigenes gen. nov., sp. nov., a novel strictly anaerobic, Gram-negative, propionate-producing bacterium isolated from plant residue in irrigated rice-field soil in Japan.

A strictly anaerobic, propionate-producing bacterial strain (WB4T) isolated from rice plant residue in anoxic rice-field soil in Japan was characterized phenotypically and phylogenetically. Cells were Gram-negative, non-motile, non-spore-forming, short rods. The strain utilized various sugars and produced propionate and acetate as major fermentation products with a small amount of succinate. The optimum growth temperature was 30 degrees C. Oxidase, catalase and nitrate-reducing activities were negative. The major cellular fatty acids were anteiso-C(15 : 0), C(15 : 0) and anteiso-C(17 : 0) 3-OH. Menaquinone MK-8(H4) was the major respiratory quinone. The genomic DNA G+C content was 39.3 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence placed the strain in the phylum 'Bacteroidetes'. The closest relative to strain WB4T was an environmental clone from water contaminated with equine manure (sequence similarity of 99.7 %) and the strain formed a distinct cluster with other environmental clones mainly from freshwater sediments. The closest recognized species were members of the genus Dysgonomonas, with 16S rRNA gene sequence similarities of 90.9-89.8 %. Bacteroides merdae was the next closest recognized species (similarity of 88.7 % to the type strain). Given that the ecological, physiological and chemotaxonomic characteristics of strain WB4T were different from those of any related species, a new genus and species Paludibacter propionicigenes gen. nov., sp. nov., is proposed to accommodate it. The type strain is WB4T (= JCM 13257T = DSM 17365T).