Abstract: Bacillus velezensis YL2021 has extensive antimicrobial activities against phytopathogens, and its genome harbors a catechol-type siderophore biosynthesis gene cluster. Strain YL2021 can produce siderophore in low-iron M9 medium, which demonstrated a wide range of antimicrobial activity in vitro. Using M9 medium as the basal fermentation medium, Plackett-Burman experiment, central composite design and response surface methodology were used to optimize the medium composition and culture conditions of strain YL2021 for high yield of siderophore in this study. The optimal medium composition of strain YL2021 for siderophore production was obtained as follows (g/L):glucose 19.43, NH₄Cl 1.93, KH₂PO₄ 9.02, sodium glutamate 6.00, MgSO₄ 1.75 and CaCl₂ 0.08. The optimal culture condition was as follows:culture temperature 30.0℃, initial pH value 7.0, culture time 36.5 h, rotation rate 200 r/min, 75 mL operational volume in 250 mL shake flask with inoculum 5%. Based on the fermentation condition as described above, the value of siderophore production reached 734.86 μmol/mL. Compared with that before optimization, siderophore production increased by 10.34 times. Together, our studies established an effective fermentation condition of strain YL2021 for siderophore production, which provide the theoretical basis and technical support for the efficient fermentation and application of siderophore in the future.

Key words: Bacillus velezensis, siderophore, optimization of fermentation, antimicrobial activity