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The main focus of the present study was to develop an efficient heterologous host for the production of valuable macrolide antibiotics using Streptomyces venezuelae. The S. venezuelae strain is amenable to genetic manipulation and has fast growth rate characteristics, thus it required a short culture period for metabolite production compared to other Streptomyces species. In the pikromycin PKS deletion mutant of S. venezuelae, tylosin polyketide synthase (PKS) was heterologously expressed using two compatible low-copy plasmids. The mutant
strain produced 0.5 mg/l of the 16-membered ring macrolactone, tylactone and a small amount of its derivative, desosamine-glycosylated tylactone. To improve the production level of tylactone and desosaminyl tylactone, additional copy of the positive regulatory gene, pikD, was introduced into the pikromycin PKS deletion mutant of S. venezuelae expressing tylosin PKS genes, leading to 2.7-fold and 17.1-fold enhanced production, respectively. Another approach to improve the
productivity of tylactone was to enhance ethylmalonyl-CoA pool, which is not used to generate the native polyketide, pikromycin but required the biosynthesis of tylactone. Genome analysis of S. venezuelae revealed that the crotonyl-CoA pathway genes involved in the biosynthesis of ethylmalonyl-CoA are located in the genome of S. venezuelae. RT-PCR and CoA analysis showed that L-lysine triggered the expression of crotonyl-CoA pathway genes and led to an increase of the ethylmalonyl-CoA pool and consequently resulted in the enhanced production of
tylactone. Disruption of putative ethylmalonyl-CoA mutase gene (meaA) also contributed to overproduction of tylactone. These results introduce S. venezuelae as a rapid heterologous expression system for the production of valuable secondary metabolites.