Optimization of Gibberellic Acid Production in Endophytic Bacillus cereus Using Response Surface Methodology and Its Use as Plant Growth Regulator in Chickpea

Gibberellic acid (GAs), a vital phytohormone, is necessary to increase seed germination as well as plant's health and growth. Likewise, a number of plant growth-promoting bacteria produce identical secondary metabolites which serve as plant growth stimulants. The current study focuses to investigate optimization of multiple variables for the maximum GAs production by bacterial isolates via Response surface methodology (RSM) with the help of Box-Behnken design (BBD) and its effects on seed germination and growth promotion of Cicer arietinum (Chickpea). Initially, bacterial isolates were screened on the basis of quantitative production of gibberellic acid without amendment of any precursor. Later, bacterial isolate, MEN8, was selected for peak production of gibberellic acid via BBD and a total of 50 sets of trials were finalized. RSM analysis signified maximum GAs production by the isolate up to 109.25 mu g/ml on 5th day of incubation at 35 degrees C on pH 7.0 by consuming 3 g/l fructose and 1.0 g/l ammonium chloride. The extracted gibberellic acid was purified by using Thin-layer chromatography, elucidated on R-f value 0.72 with gray-colored spot which was further confirmed by High-performance liquid chromatography technique, at 2.68 retention time (R-t). The MEN8 isolate was molecularly identified up to species level as Bacillus cereus by using 16S rRNA gene sequencing and phylogeny. As a final point, in vitro analysis confirmed that B. cereus MEN8 was a significant isolate for increasing seed germination parameters such as germination energy (GE-27%), capacity (GC-32%), index (GI-42%), percentage (GP-55%), vigor index (VI-89%), and vegetative growth parameters including root/shoot length and fresh/dry weight. Plant growth-promoting nature of B. cereus MEN8 creates a future avenue to be utilized as 'phytohormone-producing bioinoculant' for sustainable agriculture at commercial implications.

Automated summary

By optimizing multiple variables such as temperature, pH, carbon and nitrogen sources, the production of gibberellic acid (GAs) by bacterial isolates was maximized, leading to positive effects on seed germination and growth promotion of Chickpea plants.