A cellulolytic bacterium, strain P2-1 T , isolated from soil in Thailand, was characterized using a taxonomic approach based on phenotypic and chemotaxonomic characteristics and the 16S rRNA gene sequence. The novel strain was Gram-positive, facultatively anaerobic, spore-forming and rod-shaped. It contained meso-diaminopimelic as the diagnostic diamino acid in the cell-wall peptidoglycan. The DNA G+C content was 52.7 mol%. The major isoprenoid quinone was MK-7. Anteiso-C 15 : 0 and iso-C 16 : 0 were the dominant cellular fatty acids. Phylogenetic analyses using the 16S rRNA gene sequence showed that the novel strain was affiliated to the genus Paenibacillus. Strain P2-1 T was closely related to Paenibacillus cineris KCTC 3998 T , P. favisporus KCTC 3910 T and P. rhizosphaerae KCTC 13015 T with 96.3-96.5 % gene sequence similarity. DNA-DNA relatedness, physiological characteristics and some biochemical characteristics clearly distinguished strain P2-1 T from related species of the genus Paenibacillus. Therefore, strain P2-1 T represents a novel species of the genus Paenibacillus, for which the name Paenibacillus cellulositrophicus sp. nov. is proposed. The type strain is P2-1 T (5KCTC 13135 T 5PCU 305 T 5TISTR 1888 T ).The genus Paenibacillus as proposed by Ash et al. (1994) has undergone considerable changes as the number of recognized members of the genus has increased. At the time of writing, there were 94 recognized species in the genus. Members of the genus Paenibacillus have been isolated from very diverse environments such as soils, cattle faeces, dead honeybees, honeybee larvae, plant roots, food, warm springs, raw and heat-treated milk and from blood cultures (Berge et al., 2002;Chou et al., 2007;Roux & Raoult, 2004;Scheldeman et al., 2004;Shida et al., 1997; Velázquez et al., 2004). Some of these bacteria produce diverse assortments of extracellular polysaccharide-hydrolysing enzymes (Aÿ et al., 1998; Dasman et al., 2002;Zamost et al., 1991;Hespell, 1996;Lee et al., 2000;Morales et al., 1995;Nielsen & Sørensen, 1997). The cellulose-and xylan-degrading members of the genus Paenibacillus include the species P. barcinonensis, P. campinasensis, P. curdlanolyticus, P. favisporus, P. phyllosphaerae, P. xylanilyticus, P. panacisoli, P. siamensis, P. septentrionalis, P. montaniterrae, P. thailandensis and P. nanensis, as well as unidentified Paenibacillus spp. (Khianngam et al., 2009a, b;Ko et al., 2007;Pason et al., 2006;Rivas et al., 2005a Rivas et al., , b, c, 2006 Sánchez et al., 2005;Ten et al., 2006; Velázquez et al., 2004;Wang et al., 2008). In this paper, a novel cellulolytic bacterium isolated from Thai soil is described based on its phenotypic and chemotaxonomic characteristics and on 16S rRNA gene sequence analyses.A cellulolytic bacterial strain was isolated from a soil sample collected from Pua district in Nan province, in the northern part of Thailand. The novel strain was isolated using the spread plate method on CMC agar medium (l 21 : 1 g carboxymethylcellulose, 5 g peptone, 1 g yeast extr...