Abstract:

Objective Bafilomycins are a class of macrolide compounds produced by the fermentation of Streptomyces griseobrunneus, which have antagonistic effect on a variety of plant fungi, and its representative compound is bafilomycin A1 (Baf A1). In order to further enhance the yield of Baf A1 in Streptomyces sp. FIM-B0711 and reduce the production cost, the high-yielding strain of Baf A1 was selected and its fermentation process was optimized. Method High-yield mutant strains were generated through ultraviolet mutagenesis, followed by optimization of the fermentation process using single factor experiment, the steepest ascent experiment, and response surface methodology. Result The Baf A1 yield of the UV-21 strain reached 397.99 mg/L, representing a 23.60% increase compared to the original strain. Single factor experiment identified that maltodextrin, soybean peptone, and calcium carbonate were as the optimal carbon source, nitrogen source, and inorganic salt for strain UV-21, respectively. The optimal culture conditions were determined to be pH 7.0, an inoculum concentration of 3% (volume fraction), a liquid volume of 30 mL/250 mL, and a fermentation time of 96 h. The steepest ascent experiment revealed that the highest relative titer of 147.18% was achieved with a carbon source concentration of 45 g/L, nitrogen source concentration of 15 g/L, and inorganic salt concentration of 0.5 g/L. The response surface optimization demonstrated that the optimal fermentation process for the strain involved maltodextrin at 45.98 g/L, soybean peptone at 14.96 g/L, calcium carbonate at 0.48 g/L, valine at 3 g/L, an initial pH of 7.0, an inoculum concentration of 3% (volume fraction), a liquid volume of 30 mL/250 mL, and a fermentation time of 96 h. Under these optimized conditions, the fermentation titer reached 627.58 mg/L, a 57.69% increase compared to the initial process. Conclusion A high-yield Baf A1 strain with 627.58 mg/L is obtained based on ultraviolet mutagenesis and medium response surface optimization experiment, which increases the yield by 57.69% compared to the original strain FIM-B0711.

Key words: bafilomycins, Streptomyces, response surface test, fermentation optimization, ultraviolet mutagenesis, cultivation condition, process parameters