Optimization of indole-3-acetic acid production by Bacillus subtilis TIB6 using response surface methodology

The influence of carbon, nitrogen sources and tryptophan supplementation on indole-3-acetic acid (IAA) production of Bacillus subtilis TIB6 isolated from pepper rhizosphere, Tay Nguyen province of Viet Nam was investigated and obtained results showed that sucrose and yeast extract were the most favorable carbon and nitrogen sources for TIB6’s IAA production, respectively, while the presence of L-tryptophan in culture medium stimulated the formation of IAA. The student’s t-test of the Plackett-Burman design were used for screening significant factors affecting IAA producing capacity of TIB6 and obtained results showed that l-tryptophan, yeast extract concentrations and inoculation ratio were the main effecting parameters. By using central composite design (CCD) of response surface methodology (RSM), the culture conditions for TIB6 were optimized for maximum IAA production. The optimum values of variables were: L-tryptophan (0.088%), Yeast extract (0.82%) and inoculation ratio (1.65%).  At these conditions, the maximum IAA production was estimated to be 120,846 mg/L.