Optımızatıon of Condıtıons for the Productıon of Indole Acetıc Acıd by Azotobacter spp.

Azotobacter spp. are known for their ability to fix nitrogen into the soil non-symbiotically. Their activities can be enhanced through the provision of optimum cultural conditions. Hence, this study aimed  to isolate Azotobacter spp. and optimize their growth (medium and condtions) with a focus on pH, sucrose and indole acetic acid (IAA) concentrations. The counts of Azotobacter obtained from the rhizosphere of the crops ranged from 4.0 × 104 – 1.0 × 106 CFU/g. The three high IAA-producing Azotobacter spp. were identified as A. chroococcum, A. vinelandii and A. beijerinckii. They produced IAA in the absence and presence of 0.25 % tryptophan in the ranges of 0.20 – 0.36 and 604.5 – 1439.7 µg/mL respectively. However, under optimized conditions these isolates produced IAA in folds.  Optimum IAA was produced by A. chroococcum, A. vinelandii and A. beijerinckii  at pH, sucrose and tryptophan concentration ranging from 6.5 – 7.5, 2 – 3 % and 0.3 – 0.7 %. respectively. A. vinelandii produced a higher amount of IAA when compared with A. chroococcum and A. beijerinckii at the optimal conditions. These were 2001.1, 2541.1 and 2602.6 µg/mL at optimum pH 7.5, sucrose (2 %) and tryptophan (0.3%) respectively. It was concluded from these findings that, Azotobacter vinelandii is an excellent producer of plant growth promoting hormone, indole-3-acetic acid (IAA).