Isolation, characterization and morphological study of Azotobacter isolates

Among the diazotrops, great attention has been paid to the genus Azotobacter and its role in increasing the growth and health of plants. In the present study, forty two strains of Azotobacter were isolated from soil. These strains were purified and characterized through microscopical and biochemical test for cell shape, pigmentation, colony size, Gram reaction and catalase activity were identified as Azotobacter sp These strains showed wide variability to these characters. Among 42 isolates, 7 were single cocci, 7 coccidal chain and 4 were cocci in clumps. Majority of isolates i.e. 24, were small, medium and large rod shaped. Thirty two isolates were Gram –ve, catalase positive and 10 were Gram +ve, catalase negative. Finally from these isolates, twenty two were confirmed as Azotobacter strains on cyst formation. The carbon-source utilization pattern revealed that out of 22 strains that 16 strains resembled the characters of A. chroococcum, 3 matched with A. vinelandii and 3 with A. beijerinckii. All 22 isolates were analyzed for its nitrogen fixing ability by using Microkjeldhal method. The highest amount of N2 (18.88 mg g-1 sucrose) was fixed by Azo-SBT 72 while lowest (6.04 mg g-1 sucrose) by Azo-SUR 25 strain. However, injudicious and hazardous use of chemical fertilizers have degraded the soil health and there is need of ecofriendly management of soil by screening and hunting of potential nitrogen fixing strains to protect the soil environment and health. In this context, biofertilizers hunting natural environment is the need of soil to ensure better health of future generations