Isolation and Characterization of Indole-3-Acetic Acid producing Bacterial Root Endophytes Associated with Brown Arson (Brassica Rapa L.)
In the present study a total of 81 bacterial root endophytes were isolated and screened for IAA production in
Luria Bertani broth without supplementation of L-tryptophan and only 54.3% (44 isolates) produced IAA with the overall
average production of 8.15 μg/mL. The seventeen isolates exhibiting IAA production of ≥ 9 μg/mL were optimized using Ltryptophan
supplementations at different concentrations and incubation periods. Study on various concentrations of Ltryptophan
viz. 0.05, 010, 0.15, 0.20 and 0.25 mg/mL on indole-3-acetic acid production revealed maximum IAA production
(32.41 μg/mL) at 0.20 mg/mL L-tryptophan concentration and lowest IAA production of 16.21 μg/mL at 0.05 mg/mL
concentration. All the isolates followed almost the similar trend with maximum production at 0.2 mg L-tryptophan/mL
except the isolates SB41 and SB61 in where peak IAA production occurred at 0.15 mg/mL L-tryptophan concentration.
Highest IAA was produced by the isolate SB28 (62.92 μg/mL) at 0.2 mg L-tryptophan/mL and lowest by SB19 (11.10
μg/mL) at 0.05 mg L-tryptophan/mL. The effect of incubation period viz. 48, 96 and 144 h also affected IAA production by
bacterial root endophytes. The averag e highest IAA production of 28.80 μg/mL was at incubation period of 96 hour and
lowest average production of 19.99 μg/mL was observed at 48 hour incubation. All the 44 isolates producing IAA were
identified by amplifying their 16s rRNA genes and observed to be different species of Bacillus, Pseudomonas,Curvibacter,
Comamonas, Microbacterium, Arthrobacter, Pantoea,Okibacterium, Salinivibrio, Paenibacillus.
Keywords - IAA, tryptophan, incubation period, Pseudomonas, Bacillus