Optimization of indole-3-acetic acid production by Bacillus subtilis strain IA3

Indole-3-Acetic Acid (IAA) is a crucial plant growth-promoting hormone produced as a secondary metabolite by various microorganisms. The present study aims to isolate and screen IAA-producing endospore-forming bacteria from soil samples collected in Vietnam. A total of ten bacteria were isolated, and they were shown to have the ability to produce IAA, with strain IA3 exhibiting the highest production. Strain IA3 was identified as Bacillus subtilis based on the 16S rRNA sequencing and subsequently used to optimize conditions for IAA production. To maximize IAA yield, key factors influencing production were analyzed using Box-Behnken design. The optimized conditions led to a maximum IAA production of 47.67 ± 0.78 g/mL under the following conditions: 15.65 g/L molasses, 1.06 g/L (NH4)2SO4, and 0.52 g/L tryptophan. Therefore, Bacillus subtilis IA3 has potential applications for stimulating and enhancing plant growth or crop production.