Isolation and Characterization of Azotobacter and Phosphate Solubilizing Bacterial Isolates

Isolation from 20 soil samples collected from rhizosphere of watermelon was done on Ashby's medium and Pikovskaya's agar media.8 Azotobacter and 6 Phosphate solubilizing bacteria PSB isolates were obtained from all samples. All the obtained isolates of Azotobacter sp and PSB were gram negative. On morphological study it was observed that, all Azotobacter isolates were motile and positive for KOH test. In case of PSB, the colony shapes of 4 obtained isolates were circular and irregular in 2. All the isolates showed smooth appearance on the media with white colony colour. The biochemical results for both Azotobacter spp and PSB revealed that, most of them were positive for methyl red test, catalase test, starch hydrolysis, gelatine hydrolase test, oxidase test and indol test. Out of eight Azotobacter isolates, Isolate 4 (Azob-1) showed highest (14.25 mg/ml) N fixing ability whereas, from of six PSB isolates, Isolate1 (PSB-1) showed highest solubilising index (4.13) therefore these two isolates were found most efficient in their roles and therefore recommended for use for field experiments.