A Note on the Estimation of Azotobacter Densities by Membrane Filter Technique

1 Membrane filter technique is recommended for routine analysis of water and soil particularly those with low Azotobacter density. 2 Tests of four brands of membrane filters used for enumerating different groups of bacteria showed that highest Azotobacter counts were obtained with Millipore and Sartorius membranes. 3 Boiling of the membranes for 5 min in distilled water leads to the removal of possible substances toxic to the development of Axotobacter cells which was demonstrated by the increase of the recovered colonies, and to equal estimates obtained with the various brands.