Minimal polyketide pathway expression in an actinorhodin cluster-deleted and regulation-stimulated Streptomyces coelicolor.

Along with traditional random mutagenesis-driven strain improvement, cloning and heterologous expression of Streptomyces secondary metabolite gene clusters have 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. In this study, we generated a polyketide non-producing strain by deleting the entire actinorhodin cluster from the chromosome of a previously generated S. coelicolor mutant strain, which was shown to stimulate actinorhodin biosynthesis through deletion of two antibiotic downregulators as well as a polyketide precursor flux downregulator (Kim et al. in Appl Environ Microbiol 77:1872-1877, 2011). 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. Aloesaponarin II production was detected only in the presence of a pathway-specific regulatory gene, actII-ORF4, and its production level was the highest in the actinorhodin cluster-deleted and downregulator-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 indigenous or foreign polyketide pathways derived from diverse actinomycetes in nature.