Isolation and screening of native azotobacter from salt affected soils and measurement of their growth promoting properties

Salinity as one of the major abiotic stresses severely affects crop productivity. Plant growth promoting bacteria is being considered to ameliorate salinity stress. Fifteen samples of salt affected soils from Golestan province were collected to isolate Azotobacter. Thirty- two bacterial isolates were isolated and purified. Physiological and biochemical tests confirmed twenty-three isolates belongs to Genus Azotobacter. The isolates were assessed for their growth in liquid medium supplemented with 2, 5 and 10 % of salt. Exopolysaccharide production, drought stress tolerant and some selected growth promoting properties such as nitrogen fixation, solubilization insoluble potassium, tri-calcium phosphate solubilization, indole acetic acid and hydrogen cyanid production capability was evaluated. Results showed that increasing salt concentration had negative effect on bacterial growth. Exopolysaccharide production (0.4-5.6 g L-1) was positive by 78.2% of the isolates. Higher levels of polyethylene glycol reduced growth of the isolates. Plant growth promoting tests showed tri-calcium phosphate solubilization (52.5-218.1 gL-1), IAA production (2.4 - 60.2 mg L-1), potassium solubilization (12.9-28.3 mg L-1) and biological nitrogen fixation (2.9 - 5.1 nmol ethylene hr-1). Among the 23 isolates to Azotobacter, based on physiological tests of bacteria in different levels of salt and drought and PGPR tests, isolate AZ13 was selected as the superior isolate.