Molecular characterization and stress tolerance level of nitrogen-fixing Azotobacter strain isolated from Oryza sativa

Characterization of four isolates obtained from Oryza sativa nodules grown under a stress environment was performed. Isolates were screened for their ability to tolerate different abiotic stresses; extreme temperature (50◦ C), salinity (1–5% (w/v) NaCl), and pH (4–12). The genomic analysis of 16S rRNA showed that isolates were phylogenetically related to Azotobacter spp. All the isolates can tolerate NaCl up to 3% and be able to grow between 30 and 40 ◦C with a pH tolerance of between 6 -10 indicating that the isolates were alkali and NaCl-tolerant. The tested isolates effectively utilize mono and disaccharides as carbon sources. Out of four, Azotobacter vinelandii (AR-3) showed the highest nitrogenase fixing ability. The plant growth-promoting characterization of all isolates revealed their effectiveness to solubilize inorganic phosphate (78-288 µg mL−1), and synthesizing indole acetic acid (IAA) (46–70 µg m.). The present finding revealed that treatment A. vinelandii (AR-3) are highly efficient to improve the growth and yield of rice crop, therefore the amplification of its nitrogen fixing gene can be explored as rice biofertilizer to enhance yield and N2-fixation for the resource-poor farmers of Kuje Area Council.