Optimization and scaling-up of fermentation process for ascomycin

Abstract:

[Background] Ascomycin (FK520) is a macrolide synthesized by Streptomyces hygroscopicus, with various bioactivities. In addition, FK520 is the starting ingredient for chemical synthesis of the immunosuppressant pimecrolimus, demonstrating important application value. [Objective] To achieve large-scale production of FK520 by fermentation, we focused on the optimization and scaling-up of the fermentation processes in 1-L and 15-L fermenters with S. hygroscopicus ATCC 14891. [Methods] Strain ATCC 14891 was fermented in a 250-mL shake flask, which was further scaled-up to a 15-L fermenter. We appropriately reduced the initial carbon and nitrogen sources, removed soybean oil, and decreased manganese and magnesium salts in the 15-L fermenter to increase the FK520 titer. Further experiments in 1-L parallel bioreactors were conducted to reveal the optimal pH and ammonium ion concentration for fermentation. The exogenous precursor lysine was added during the process to further increase the FK520 titer in the 15-L fermenter. [Results] The FK520 titer reached 414 mg/L after fermentation in a 250-mL shake flask for 120 h, and the titer decreased by 30.92% to 286 mg/L when the fermentation was scaled-up to a 15-L fermenter. After appropriate reducing of the initial carbon and nitrogen sources, the titer increased by 56.99%. The removal of soybean oil and reduction of manganese and magnesium salts by 20% to improve dissolved oxygen increased the titer by 78.32% and 101.75%, respectively. Further experiments conducted in 1-L parallel bioreactors revealed that the optimal pH and ammonium ion concentration for fermentation were 5.5 and 5 mmol/L, respectively. Based on the optimal pH and ammonium ion concentration and the 20% reduction in manganese and magnesium salts, the exogenous precursor lysine was added during the process in the 15-L fermenter, under which the FK520 titer reached 717 mg/L, 1.5 times higher than that of the control fermenter. Moreover, the consumption of glycerol was significantly reduced, which was only 25.91% of that in the control fermenter. [Conclusion] The above fermentation control process laid a foundation for the subsequent process optimization and scaling-up of fermentation for FK520 production.