Selection of Efficient EPS Producing and Cyst Forming Azotobacter Isolates under Stress Condition

Azotobacters are unique biofertilizers to maintain the N level in agricultural soil and synthesize the plant growth promoting hormones as indole acetic acid and gibberellins. Azotobacter EPS in the soil habitat play key roles in ecosystem functioning through controlling nutrient cycling reactions essential for maintaining soil fertility and also contributing to the genesis and maintenance of soil structure under conventional, biotic, and abiotic stressed soil environment. In the present investigation, attempts have been made to isolate efficient strains of Azotobacter from different locations of Tamil Nadu for the production of exopolysaccharide and cyst under induced stress conditions. Based on exopolysaccharide production, three efficient Azotobacter isolates viz. , AztRMD2 (1.755 g/50ml), AztPMK1 (1.56 g/50ml) and AztPMK2 (1.353 g/50ml) were selected for studying the cyst formation. The effect of limiting conditions of specific single micronutrient, combination of two micronutrients, reduced sucrose concentrations and addition of n- butanol as a carbon source on the induction of cyst formation was evaluated. The AztRMD2 isolate showed maximum cyst formation of around 50 - 85 % with elimination of magnesium from the growth medium, followed by AztPMK1. The results indicated that AztRMD2 can withstand upto 4 % NaCl concentration whereas maximum polysaccharide production was noticed in the broth containing 0.02 % of NaCl concentration. For artificial soil aggregation, AztRMD2 showed maximum pore space percentage (52.5 %) and minimum bulk density (1.12g/cc). The aggregation stability (45stable aggregates) was also high in this isolate compared to Control. The results indicated that AztRMD2 performed better than the standard strains.