Diversity of cell morphology, nitrogenase activity and dna profile of azotobacter isolates from soils of Maharashtra

A total of 94 Azotobacter isolates were recovered during the year 2010 from the rhizosphere soils of six different physiographic regions of Maharashtra. The distinct variation was observed in cell morphology among different isolates. All isolates were positive for starch hydrolysis, H₂ S production, catalase and oxidase test, but were negative for gelatin liquefaction. Mannitol, glucose, sucrose and fructose were used as a carbon source by all isolates, while malate and citrate gave negative results. All isolates were identified as Azotobacter chroococcum. A significant variation was observed in nitrogenase activity (19.5 to 217.3 nmol C₂ H₄.mg protein⁻¹. hr⁻¹). The isolates from Marathwada exhibited higher average nitrogenase activity (103.0 nmol C₂ H₄.mg protein⁻¹. hr⁻¹). On the basis of UPGMA clustering analysis, Azotobacter chroococcum isolates were classified into four broad clusters. The clustering formed among the Azotobacter chroococcum isolates was due to domestication of the isolates in different agroecological regions as well as their nitrogenase activity. Based on nitrogen fixing ability, highly efficient Azotobacter isolates may be further exploited in biofertilizer production.