SUMMARY: Successful isolation of azotobacter phages from soil samples was accomplished by using a modified Burk's nitrogen-free medium with sucrose as the carbon source. The natural azotobacter flora in the soil samples served as the enrichment strains and the medium was not further enriched by the addition of laboratory cultures of the bacteria. Phage titres as high as 5.5 x 10 plaque-forming units/ml. were obtained when the indicator strain for phage assays was O. On the basis of plaque morphology, nine phage isolates were obtained and purified by standard techniques. The plaques formed by the phages consisted of a central clear area surrounded by a halo and ranged from 1 to 7 mm. in diameter. Antiphage sera were produced in rabbits against a previously isolated phage and the new isolates; on the basis of cross-neutralization experiments with homologous and heterologous antisera, the 10 phases were placed into four major serological groups. Groups I and II contained four phages each, and groups III and IV contained one phage each. The degree of serological relatedness among the phages within groups I and II was investigated. A survey of 48 azotobacter strains showed that 11 out of 12 strains and 14 out of 25 strains showed plaque formation by one or more of the phages. Strains of and were not lysed by the phages. The value of the present series of phages in the classification of the genus was discussed.


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