Nitrogen fixation in Pseudomonas stutzeri

A recently developed oxygen gradient system and a complex medium were used to isolate a microaerobically N₂-fixing heterotrophic bacterium from the rhizosphere of a high fixing Sorghum nutans cultivar. The isolate was identified as nif(+) phenotype of Pseudomonas stutzeri on the basis of cultural, physiological and biochemical characteristics, including DNA/DNA hybridization. N₂ fixation was demonstrated by assimilation of ¹⁵N₂ into cellular protein; the physiology of nitrogen fixation was studied. The isolate contains one 30 MD plasmid and can be cured with associated loss of N₂ fixation capability.Dedicated to Prof. Dr. W. Nultsch on the occasion of his 60th birthday