Enhanced production of ansamitocin P-3 by addition of Mg2+ in fermentation of Actinosynnema pretiosum

► Effective strategy by Mg2+ addition was developed to increase antitumor AP-3 production. ► Addition time and dosage of Mg2+ were critical to AP-3 production by Actinosynnemapretiosum. ► Decreased intermediates level and increased enzyme activities were observed by addition of Mg2+.