Pseudomonas azotifigens sp nov., a novel nitrogen-fixing bacterium isolated from a compost pile

A nitrogen-fixing bacterium, designated strain 6H33b(T), was isolated from a compost pile in Japan. The nitrogenase activity of this strain was detected based on its acetylene-reducing activity under low oxygen concentrations (2-4%). An analysis of the genes responsible for nitrogen fixation in this strain, nifH and nifD, indicated a close relationship to those of Pseudomonas stutzeri A15 (A1501). Sequence similarity searches based on the 16S rRNA gene sequences showed that strain 6H33b(T) belongs within the genus Pseudomonas sensu stricto; closest similarity was with Pseudomonas indica (97.3%). A comparison of several taxonomic characteristics of 6H33b(T) with those of P. indica and some type strains of the genus Pseudomonas sensu stricto indicated that 6H33b(T) could be distinguished from P. indica based on the presence of nitrogen fixation ability, the absence of nitrate reduction and denitrification abilities and the utilization of some sugars and organic acids. Phylogenetic analyses and the results of DNA-DNA hybridization experiments also indicated that strain 6H33b(T) represents a species distinct from P. indica. From these results, it is proposed that strain 6H33b(T) (=ATCC BAA-1049(T)=JCM 12708(T)) is classified as the type strain of a novel species of the genus Pseudomonas sensu stricto under the name Pseudomonas azotifigens sp. nov.