Medium optimization and subsequent fermentative regulation enabled the scaled-up production of anti-tuberculosis drug...

Tuberculosis (TB) and its evolving drug resistance have exerted severe threats on the global health, hence it is still essential to develop novel anti-TB antibiotics. Ilamycin-E1/E2 is a pair of cycloheptapeptide enantiomers obtained from a marine Streptomyces atratus SCSIO ZH16-ΔilaR mutant, and has presented significant anti-TB activities as promising drug lead compounds, but their clinical development has been hampered by low fermentation titers.

By applying the statistical Plackett-Burman design (PBD) model, bacterial peptone was first screened out as the only significant but negative factor to affect the ilamycin-E1/E2 production. Subsequent single factor optimization in shaking flasks revealed that the replacement of bacterial peptone with malt extract could not only eliminate the accumulation of porphyrin-type competitive byproducts but also improve the titer of ilamycin-E1/E2 from original 13.6 ± 0.8 to 142.7 ± 5.7 mg L^-1 , about 10.5-fold increase. Next, a pH coordinated feeding strategy was adopted in 30 L fermentor and obtained 169.8 ± 2.5 mg L^-1 ilamycin-E1/E2, but further scaled-up production in 300 L fermentor only gave a titer of 131.5 ± 7.5 mg L^-1 due to the unsynchronization of feeding response and pH change. Consequently, a continuous pulse feeding strategy was utilized in 300 L fermentor to solve the above problem and finally achieved 415.7 ± 29.2 mg L^-1 ilamycin-E1/E2, representing a 30.5-fold improvement.

Our work has provided a solid basis to acquire sufficient ilamycin-E1/E2 lead compounds and then support their potential anti-TB drug development.