sp. nov., a plant polysaccharide-decomposing anaerobic bacterium isolated from a methanogenic reactor.

An obligately anaerobic bacterial strain (WR041) was isolated from a plant residue sample in a methanogenic reactor. Cells of the strain were Gram-stain-negative, non-motile, non-spore-forming rods. JCM 13650 was the closest species of the strain based on 16S rRNA gene sequencing (98.9 % similarity). Genome analysis of strain WR041 indicated that the genome size of the strain was 3.52 Mb and the genomic DNA G+C content was 37.5 mol%. Although the 16S rRNA gene sequence similarity of strain WR041 with the closest species was higher than the threshold value of the recommended species delineation (98.7 %), the average nucleotide identity and the digital DNA-DNA hybridization value between them were 91-92 and 45.5 %, respectively, suggesting that strain WR041 represents a novel species in the genus. Strain WR041 essentially required haemin and CO/NaCO for growth. The strain was saccharolytic and decomposed various polysaccharides (glucomannan, inulin, laminarin, pectin, starch and xylan) and produced acetate and succinate. The optimum growth conditions were 35 °C and pH 6.8. The major cellular fatty acids were branched-chain fatty acids such as anteiso-C and iso-C. Menaquinones MK-11 and MK-12 were the major respiratory quinones. Many protein-coding genes which were not found in the genome of as orthologous genes were detected in the genome of strain WR041. Based on the differences in the phylogenetic, genomic and physiological characteristics between strain WR041 and related species, the name sp. nov. is proposed to accommodate strain WR041 (=NBRC 115134 = DSM 112534).