A total of 21 bacterial isolates (Azotobacter sp., 10 and fluorescent Pseudomonas sp., 11) were isolated from different rhizospheric soils in the vicinity of Aligarh city and characterized as per standard methods. These isolates were further tested for the production of indole acetic acid (IAA) in a medium with 0, 1, 2 and 5 mg/ml of tryptophan. | Turk J Biol 29 (2005) 29-34 © TÜB‹TAK Indole Acetic Acid Production by the Indigenous Isolates of Azotobacter and Fluorescent Pseudomonas in the Presence and Absence of Tryptophan Farah AHMAD, Iqbal AHMAD, Mohd Saghir KHAN Department of Agricultural Microbiology, Faculty of Agricultural Sciences, Aligarh Muslim University, Aligarh - 202002 INDIA Received: Abstract: A total of 21 bacterial isolates (Azotobacter sp., 10 and fluorescent Pseudomonas sp., 11) were isolated from different rhizospheric soils in the vicinity of Aligarh city and characterized as per standard methods. These isolates were further tested for the production of indole acetic acid (IAA) in a medium with 0, 1, 2 and 5 mg/ml of tryptophan. A low amount ( mg/ml) of IAA production was recorded by Azotobacter strains without tryptophan addition. Seven Azotobacter isolates showed high level ( to mg/ml) production of IAA at 5 mg/ml of tryptophan while at 1 and 2 mg/ml the production was in the range of to and to mg/ml, respectively. Production of IAA in fluorescent Pseudomonas isolates increased with an increase in tryptophan concentration from 1 to 5 mg/ml in the majority of isolates. In the presence of 5mg/ ml of tryptophan, 5 isolates of Pseudomonas produced high levels ( to mg/ml) of IAA while 6 other isolates produced IAA in the range of to mg/ml. Production of IAA was further confirmed by extraction of crude IAA from 3 isolates of Azotobacter (Azs1, Azs6 and Azs9 ) and three isolates of Pseudomonas (Ps1, Ps4 and Ps7) and subsequent TLC analysis. A specific spot from the extracted IAA preparation was found corresponding with the standard spot of IAA with same Rf value. Pseudomonas isolates (Ps1, Ps4 and Ps7) showed inhibitory effects on the growth of root elongation of Sesbania aculeata and Vigna radiata at all concentrations of tryptophan compared to the control. However, the isolates of Azotobacter (Azs1, Azs6 and Azs9) .
