Process optimization with alternative carbon sources and modulation of secondary metabolism for enhanced ansamitocin P-3 production in Actinosynnema pretiosum

Ansamitocin P-3 (AP-3), synthesized by Actinosynnema pretiosum, is a microtubule disruptor with significant antitumor activity. Although efforts have been made for the study of ansamitocin biosynthetic gene clusters and its fermentation improvement, the yield and productivity of AP-3 are still limited. In this study, fructose was found to be more beneficial to AP-3 production than glucose, and the culture condition was optimized via single-factor experiments and response surface method. The AP-3 concentration in the Erlenmeyer flasks reached 144 mg/L with the optimized medium containing fructose 9.36 g/L, glycerol 26.79 g/L and soluble starch 3.03 g/L, increased by ninefold compared with that before optimization. The result of medium optimization showed that fructose was an important element for effective increase in AP-3 production. Transcription of genes involved in primary metabolism and ansamitocin biosynthetic pathway was investigated to elucidate metabolic responses of cell metabolism to the substitution of fructose for glucose. It was demonstrated that using fructose as the major carbon source could relieve glucose repression and therefore result in flux rearrangement in primary metabolism for better providing biosynthetic precursors and stimulating the secondary metabolism in A. pretiosum. The results obtained might be of particular benefit to further enhancement of ansamitocin productivity.