Eight psychrotolerant, xylan-degrading strains of bacteria that were catalase-positive, oxidase-negative and able to reduce nitrate to nitrite were isolated from soil beneath moist non-acidic and acidic tundra in northern Alaska. The DNA G+C contents for the strains ranged from 46.4-50.3 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that each strain belonged to the genus Paenibacillus. The highest level of 16S rRNA gene similarity was found between the eight strains and Paenibacillus amylolyticus NRRL NRS-290(T) (98.9-99.1 %). However, despite relatively high 16S rRNA gene similarity, DNA-DNA hybridization, repetitive elements genotyping and phenotypic analysis revealed that at least two of the strains differed from P. amylolyticus NRRL NRS-290(T). DNA-DNA hybridization values between strain A10b(T) and P. amylolyticus NRRL NRS-290(T) (4.3 %), between strain B22a(T) and P. amylolyticus NRRL NRS-290(T) (48.8 %) and between strain A10b(T) and strain B22a(T) (11.0 %) were below those recommended by the ad hoc committee for those belonging to the same species. Significant phenotypic features that differentiate these novel strains from P. amylolyticus included their inability to utilize l-arabinose and ability to utilize glycogen as sole carbon sources. Unlike strains 1B4a and B22a(T), strains A6a and A10b(T) produced ethanol as an end product of glucose fermentation, utilized acetic acid and 2,3-butanediol and did not utilize d-gluconic acid. MK-7 was the major isoprenoid quinone and anteiso-C(15 : 0) was the most abundant fatty acid for strains A10b(T) and B22a(T). On the basis of these results, strains A10b(T) and B22a(T) are each considered to represent a novel species of the genus Paenibacillus, for which the names Paenibacillus tundrae sp. nov. and Paenibacillus xylanexedens sp. nov. are proposed, respectively. The type strain of Paenibacillus tundrae sp. nov. is A10b(T) (=NRRL B-51094(T)=DSM 21291(T)). The type strain of Paenibacillus xylanexedens sp. nov. is B22a(T) (=NRRL B-51090(T)=DSM 21292(T)).