Abstract
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. Key words: L-tryptophan, indole-3-acetic acid, plant growth promoting rhizobacteria, indole pyruvate decarboxylase.
Highlights
Rhizospheric colonization of cereal crop plants and plant growth promoting activity involving indole-3-acetic acid (IAA) production by Klebsiella sp. and Bacillus sp. has been well documented (El-khawas and Adachi, 1999; Mishra and Kumar, 2012; Saharan and Nehra, 2011)
Literature survey show that the highest accumulation of IAA occurs in the presence of L-tryptophan after 96 h of growth (Bhattacharya and Basu, 1992), which is in accordance with the present study
Since pH of the culture medium directly influences the growth of the strain, studies suggest either release of IAA under in vitro condition is the major cause of decrease in pH of the culture medium or accumulation of IAA is directly proportional to decrease in pH
Summary
Rhizospheric colonization of cereal crop plants and plant growth promoting activity involving indole-3-acetic acid (IAA) production by Klebsiella sp. and Bacillus sp. has been well documented (El-khawas and Adachi, 1999; Mishra and Kumar, 2012; Saharan and Nehra, 2011). Rhizospheric colonization of cereal crop plants and plant growth promoting activity involving indole-3-acetic acid (IAA) production by Klebsiella sp. L-tryptophan serves as a physiological precursor for biosynthesis of IAA in plants and in microbes (Woodward and Bartel, 2005). Synthesis of IAA depends on environmental conditions, availability, uptake and rate of deamination of precursor, the types of soil nutrients, metabolites released and the preferred pathways involved (Spaepen et al, 2007; Woodward and Bartel, 2005). L-tryptophan dependent biosynthesis of IAA involving ipdc, indole-3acetamide (iam) and indole-3-acetonitrile (ian) gene has been well documented in plant growth promoting rhizobacteria (PGPR) (Duca et al, 2014). Many workers have acknowledged the role of PGPR and significant advancements have been made in this interesting area of research but there are still gaps left especially on molecular aspect, which needs further study
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