Nitrogen Fixation by Gram-Negative Bacteria

Abstract

ALTHOUGH claims for nitrogen fixation by Gram-negative bacteria other than the Azotobacter have been made in the past¹, confirmation of such claims is comparatively recent^2–5. Nitrogen fixation by particular strains of Pseudomonas has been reported by Anderson² and by Voets and Debacker³. Recently, Jensen⁵ isolated from a Danish water-course a nitrogen-fixing organism that appears to be a species of Achromobacter. In most of these studies, the investigators were attempting to obtain species such as Azotobacter that are known to fix nitrogen; hence the techniques employed would select for this characteristic. Because of the significance of the discovery of these new agents for both theoretical and applied biology we have examined strains of Pseudomonas and Achromobacter that had been isolated under non-selective conditions.