Biosynthesis of indole-3-acetic acid by plant growth promoting rhizobacteria, Klebsiella pneumonia, Bacillus amyloliquefaciens and Bacillus subtilis

Indole-3-acetic acid biosynthetic activity of Klebsiella pneumonia, strain MR-M1, Bacillus amyloliquefaciens strain MR-AI, four Bacillus sp. strain MR-SP, RR-R2, WR-W2 and MR-Z1 were investigated. Here, the authors demonstrated the effect of carbon sources, amino acids, vitamins and abiotic stress on the indole-3-acetic acid (IAA) production level under in vitro condition by the six strains. The culture medium was exogenously supplemented with L-tryptophan (200 μg/ml) and incubated for 96 h. IAA biosynthesis was further confirmed by indole-3-pyruvate decarboxylase encoding ipdc gene amplification. Succinate followed by acetate followed by malate was observed as the most preferred carbon source for IAA production. Stimulation of IAA production at pH 6.0, 0.1% salinity and 32°C temperature after 96 h of growth in presence of L-tryptophan was observed. The highest amount of IAA production was observed in strain MR-M1 followed by WR-W2. Decreasing trend of IAA levels was observed in the presence of vitamins and amino acids as compared to the control. The amplicon of 250 bp was observed in all the six rhizospheric strains. Taken together, the result shows that L-tryptophan stimulates IAA production and strain MR-M1 was observed as the most efficient IAA producing rhizospheric bacteria.