Propionicimonas paludicola gen. nov., sp. nov., a novel facultatively anaerobic, Gram-positive, propionate-producing bacterium isolated from plant residue in irrigated rice-field soil.

Two propionate-producing strains (Wd(T) and Wf) that were isolated anaerobically from plant residue of irrigated rice-field soil in Japan were characterized phenotypically and phylogenetically. The growth rate of strain Wd(T) was very slow in basal medium, but both growth and propionate production were stimulated significantly by the addition of cyanocobalamin. Strain Wf grew well in basal medium and produced substantial amounts of fermentation products, including propionate. Other phenotypic and phylogenetic characteristics of the two isolates were almost identical. Both were facultatively anaerobic, but much better growth was observed under anaerobic conditions. Cells were Gram-positive, non-motile, non-spore-forming and pleomorphic rods with irregular V- or crescent-shaped cell arrangements. Fermentation products from glucose in the presence of excess cyanocobalamin were acetate, lactate, a small amount of succinate and CO(2), in addition to propionate. Both oxidase and catalase activities were negative. The strains possessed meso-diaminopimelic acid in their peptidoglycan and their major cellular fatty acids were C(13 : 0), anteiso-C(15 : 0) and C(15 : 0). The isolates had high genomic DNA G+C contents (68.7 and 67.4 mol%, respectively). Menaquinones MK-9(H(4)) and MK-10(H(4)) were the predominant respiratory quinones. Phylogenetic analysis based on 16S rDNA sequences placed both strains in the Actinobacteria, with Micropruina glycogenica as their closest relative (sequence similarity values of 95.8 and 95.7 %, respectively). Microlunatus phosphovorus and Friedmanniella antarctica were also related closely to the isolates. As their morphological, physiological and chemotaxonomic characteristics were distinctly different from those of any related species, Propionicimonas paludicola gen. nov., sp. nov. is proposed to accommodate these strains. The type strain of the novel species is Wd(T) (=JCM 11933(T)=DSM 15597(T)).