The growth inhibition of Azotobacter chroococcum by Pseudomonas sp.

When Azotobacter chroococcum and Pseudomonas sp. were grown together on nitrogen-deficient azotobacter agar medium, the growth of the azotobacter was inhibited. Studies were undertaken to explain this microbial interaction. No demonstrable active diffusible factor was found in cell-free filtrates (neutralized) and extracts. Experiments with indicator agar plates and HEPES-buffered liquid medium suggested that the interaction was attributable to the transformation by the pseudomonad of metabolic intermediates of azotobacter to inhibitory acidic end products. The high sensitivity of A. chroococcum to acidity resulted in the inhibition phenomenon. This microbial association is discussed briefly from the point of view of the ecology of the two species.