Functional Expression of Minimal Polyketide in a Regulation-Stimulated S. coelicolor

초록

Along with traditional random mutagenesis-driven strain improvement, cloning and heterologous expression of Streptomyces secondary metabolite gene cluster has become an attractive complementary approach to increase its production titer, of which regulation is typically under tight control via complex multiple regulatory networks present in a metabolite low-producing wild-type strain. Here, we generated a polyketide non-producing strain via deletion of the entire actinorhodin cluster from the chromosome of a previously-generated S. coelicolor mutant strain, which was proved to stimulate actinorhodin biosynthesis through deletion of two antibiotic down-regulators as well as a polyketide precursor flux down-regulator. Using this engineered S. coelicolor mutant strain as a surrogate host, a model minimal polyketide pathway for aloesaponarin II, an actinorhodin shunt product was cloned in a high-copy conjugative plasmid, followed by functional pathway expression and quantitative metabolite analysis. The aloesaponarin II production was detected only in the presence of a pathway-specific regulatory gene, actII-ORF4, and its production level was observed at the highest level in the actinorhodin cluster-deleted and down-regulators-deleted mutant strain, implying that this engineered polyketide pathway-free and regulation-optimized S. coelicolor mutant strain could be used as a general surrogate host for efficient expression of foreign or cryptic polyketide pathways derived from diverse actinomycetes in nature.