1. Ahmad N, Rai M and Sahi B P 1977 Nitrogen fixation by a salt and alkali tolerant strain ofAzotobacter chroococcum. Curr. Sci. 46, 107–108.
2. Ahmad N and Sahi B P 1979 Morphological and cultural characteristics of salt and alkali tolerant strains ofAzotobacter chroococcum (Nitrogen fixing bacteria). Curr. Sci. 48, 321–328.
3. Beijerinck M W 1901 Über oligonitrophile Mikroben. Bakteriol. Abt. 11. 561.
4. Clark H F, Geldreich E E, Jeter H L and Kabler P W 1951 The membrane filter in sanitary bacteriology. Pub. Health Rep. 66, 951.
5. Curie J H 1931 Method for the study of Azotobacter and its application to fertility plot soils. Soil Sci. 32, 9–25.