Partial activation of a silent angucycline-type gene cluster from a rubromycin beta producing Streptomyces sp. PGA64

In the course of DNA-fingerprinting our strain collection for antibiotic biosynthesis genes, two different type II polyketide synthase (PKS) gene clusters were observed from Streptomyces sp. PGA64. Phylogenetic analysis placed these together with known rubromycin and angucycline biosynthetic gene clusters. The host strain itself has a very clean production profile of secondary metabolites, which composes mainly of rubromycin beta under typical fermentation conditions. Sequencing of a 16.5 kb fragment from the putative angucycline cluster revealed eight genes that were homologous to typical type II PKS genes responsible for synthesizing aromatic polyketides. These genes were especially similar to genes from known angucycline biosynthetic gene clusters and also synteny to these clusters was observed. In addition, three genes were recognized that are needed for priming the minimal PKS complex before polyketide synthesis can initiate, but which are not normally found to cluster with antibiotic biosynthesis genes. A putative repressor gene that was dissimilar to repressor genes found from well-characterized antibiotic biosynthesis gene clusters was also discovered. Gene disruption of the repressor resulted in partial activation of the cluster and production of two angucycline metabolites, UWM6 and rabelomycin. The results confirm that the DNA-fingerprinting method we have developed can be used to correctly detect compounds that are not visible in chemical screens.