Abstract: Bacillus velezensis strain Jt84 demonstrates remarkable control efficacy against rice false smut and blasts. Previous studies have established that iturin produced by Jt84 strain is the primary bioactive compound inhibiting rice fungal pathogens' growth and spore germination. To further augment the production of the antifungal agent iturin, this study investigated the early fermentation phase of B. velezensis Jt84 by supplementing exogenous precursors, precisely various amino acids required for iturin biosynthesis. Utilizing a Plackett-Burman single-factor experimental design, we identified three principal precursor amino acids that significantly influence iturin yield: glutamic acid (Glu), serine (Ser), and glutamine (Gln). Subsequent optimization via response surface methodology revealed the optimal concentrations for these essential precursors to be Glu at 0.08 g/L, Gln at 0.17 g/L, and Ser at 0.19 g/L, with additional amino acids present at concentrations of asparagine (Asn) at 0.06 g/L, proline (Pro) at 0.06 g/L, and tyrosine (Tyr) at 0.006 g/L. Under these optimized conditions, the fermentation broth achieved a bacterial content of 3.83×10⁹ cfu/mL and the iturin yield was 0.242 g/L, representing a 26.04% increase in iturin production compared to pre-optimization levels. Furthermore, the plate inhibition assay indicated that the inhibition width against Ustilaginoidea virens increased by 23.66% compared to the initial culture medium.

Key words: Bacillus velezensis, iturin, fermentation, response surface methodology