Optimization of Indole Acetic Acid Production by Pseudomonas putida UB1 and its Effect as Plant Growth-Promoting Rhizobacteria on Mustard (Brassica nigra)

Indole-3-acetic acid (IAA) production was monitored in nine plant growth-promoting rhizobacteria isolated from the rhizospheric soil of alfalfa (Medicago sativa). The isolate producing maximum amount of IAA was identified as Pseudomonas putida UB1 by 16S rRNA partial gene sequencing. Further investigations were carried out for optimal L-tryptophan concentration and other growth parameters for IAA production by P. putida. IAA production increased when the L-tryptophan medium for IAA production was supplemented with sucrose 0.5 %, (NH4)(2)SO4 10 mg/ml, and tryptophan 0.2 mg/ml at pH 7.5. Maximum IAA production was achieved at 96 h. Production of IAA was confirmed by extraction of crude IAA and subsequent thin-layer chromatography analysis. The specific spot from the extracted IAA was found to correspond with a spot of standard IAA with the same R-f value (0.36). The crude IAA was further purified by passing it through a silica gel column. P. putida UB1 and its purified IAA were demonstrated to show stimulatory effect on mustard (Brassica nigra) plants in vitro with their incorporation in MS medium as a novel approach.