Pleomorphomonas oryzae gen. nov., sp nov., a nitrogen-fixing bacterium isolated from paddy soil of Oryza sativa

Five strains of free-living diazotrophs isolated from rice were characterized by using a polyphasic approach. The strains were found to be very closely related, with 99-100% 16S rRNA gene sequence similarity and DNA-DNA hybridization values greater than 70%, suggesting that they represent a single species. When compared with other recognized species, they showed not more than 93 and 89% similarity for the 16S rRNA and nifH gene sequences, respectively. Phylogenetic distances showed that these isolates were distinct from other taxa within the alpha-Proteobacteria. Chemotaxonomic characteristics of these isolates included the DNA G+C content (62.1-63.1 mol%), the major quinone system (Q-10), predominant fatty acids (18: 1 omega 7c, cyclo 19: 0 omega 8c and 16: 0) and major hydroxy fatty acids (14:0 3-OH, 18:0 3-OH and 16:0 3-OH). Based on phylogenetic and phenotypic analyses, these isolates are considered to represent a novel genus and species, for which the name Pleomorphomonas oryzae gen. nov., sp. nov. is proposed. The type strain is F-7(T) (=IAM 15079(T) =ATCC BAA-940(T) =DSM 16300(T)).