An obligately anaerobic bacterial strain designated T-1-35T was isolated as a dominant cultivable cellulose-degrading bacterium from soil of a Japanese rice field as an anaerobic filter-paper degrader. Cells of strain T-1-35T stained Gram-positive and were non-spore-forming rods with rounded ends, 0.8–1.0×3.5–15.0 µm, and motile by means of two to four polar flagella. Cells of strain T-1-35T exhibited pleomorphism: in aged cultures (over 90 days of incubation), almost all cells were irregularly shaped. Although no spore formation was observed, cells tolerated high temperatures, up to 90 °C for 10 min. The temperature range for growth was 15–40 °C, with an optimum at 35 °C. The pH range for growth was 5.5–9.0, with an optimum at pH 8.0–8.5 (slightly alkaliphilic). Strain T-1-35T fermented some carbohydrates to produce ethanol and lactate as the major products. Major cellular fatty acids were iso-C16 : 0 and iso-C13 : 0 3-OH. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that strain T-1-35T belonged to Clostridium rRNA cluster III. The closest relative of strain T-1-35T was Bacteroides cellulosolvens WM2T, with 16S rRNA gene sequence similarity of 93.4 %. Phenotypic, physiological and molecular genetic methods demonstrated that strain T-1-35T was distinct from its phylogenetic relatives (members of Clostridium rRNA cluster III) because it predominantly produced ethanol, iso-C13 : 0 3-OH was a major cellular fatty acid and it always exhibited pleomorphism. On the basis of the results of a polyphasic taxonomic study, strain T-1-35T is considered to represent a novel genus and species, Anaerobacterium chartisolvens gen. nov., sp. nov. The type strain of Anaerobacterium chartisolvens is T-1-35T ( = DSM 27016T = NBRC 109520T). In addition, from the results of our phylogenetic analysis and its phenotypic features, the species Bacteroides cellulosolvens Murray et al. 1984 is proposed to be reclassified in the new genus Pseudobacteroides as Pseudobacteroides cellulosolvens gen. nov., comb. nov., with the type strain WM2T ( = ATCC 35603T = DSM 2933T = NRCC 2944T).

An obligately anaerobic bacterial strain designated KC3T was isolated from a rice straw-degrading culture, for which soil of a Japanese rice field was used as the inoculum. Cells of strain KC3 T were determined to be non-cellulolytic, Gram-stain-positive, non-motile, ellipsoidal, spore-forming rods, 0.8-1¾4-25 mm. Endospores were formed at a terminal position in elongated cells (12-25 mm, mean 15 mm). The temperature range for growth was 20-50 6C, with an optimum at 37 6C. The pH range for growth was 5.0-7.5, with an optimum at pH 6.0 (slightly acidophilic