Heterologous expression of tylosin polyketide synthase and production of a hybrid bioactive macrolide in Streptomyces venezuelae
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Tylosin polyketide synthase (Tyl PKS) was heterologously expressed in an engineered strain of Streptomyces venezuelae bearing a deletion of pikromycin PKS gene cluster using two compatible low-copy plasmids, each under the control of a pikAI promoter. The mutant strain produced 0.5 mg/l of the 16-membered ring macrolactone, tylactone, after a 4-day culture, which is a considerably reduced culture period to reach the maximum production level compared to other Streptomyces hosts. To improve the production level of tylactone, several precursors for ethylmalonyl-CoA were fed to the growing medium, leading to a 2.8-fold improvement (1.4 mg/ml); however, switching the pikAI promoter to an actI promoter had no observable effect. In addition, a small amount of desosamine-glycosylated tylactone was detected from the extract of the mutant strain, revealing that the native glycosyltransferase DesVII displayed relaxed substrate specificity in accepting the 16-membered ring macrolactone to produce the glycosylated tylactone. These results demonstrate a successful attempt for a heterologous expression of Tyl PKS in S. venezuelae and introduce S. venezuelae as a rapid heterologous expression system for the production of secondary metabolites.
KeywordsTylosin EcoRI Fragment Heterologous Host Diethylmalonate Polyketide Production
We thank Dr. Brian J. Beck for providing pBB155 and Dr. Y.S. Hong for help in constructing S. venezuelae DHS2001. We are also grateful to Professor Eric Cundliffe (University of Leicester) for kindly providing a tylactone standard. This work was supported by a grant (20050410-034-682-149-00-00) from the BioGreen 21 Program, Rural Development Administration, the 21C Frontier Microbial Genomics and Application Center Program, Ministry of Science and Technology (grant MG05-0303-4-0), Republic of Korea, and the SRC program of the Korea Science and Engineering Foundation (KOSEF) through the Center for Intelligent Nano-Bio Materials at Ewha Woman’s University (grant R11-2005-008-00000-0).
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