An endospore-forming strain, 20CMT, was isolated from Antarctic sediment and identified as a member of the genus Paenibacillus on the basis of phenotypic and phylogenetic analyses. The organism stained Gram-variable and was facultatively anaerobic. Strain 20CMT was psychrotolerant, growing optimally at 10-15 degrees C. Like other Paenibacillus species, it contained anteiso-C(15 : 0) as the major cellular fatty acid. The DNA G + C content was 40.7 mol%. 16S rRNA gene sequence analysis placed strain 20CMT within the Paenibacillus cluster, with a similarity value of 99.5 % to Paenibacillus macquariensis DSM 2T. DNA-DNA hybridization experiments between the Antarctic isolate and P. macquariensis DSM 2T revealed a reassociation value of 47 %, indicating that strain 20CMT and P. macquariensis DSM 2T belong to different species. Based on evaluation of morphological, physiological, chemotaxonomic and phylogenetic analyses, a novel species, Paenibacillus antarcticus sp. nov., is proposed; the type strain is 20CMT (= LMG 22078T = CECT 5836T).