CLONING AND NUCLEOTIDE-SEQUENCE OF A REGION OF THE KIBDELOSPORANGIUM-ARIDUM GENOME HOMOLOGOUS TO POLYKETIDE BIOSYNTHETIC GENES

The actinomycete Kibdelosporangium aridum naturally produces ardacin, a new glycopeptide antibiotic, the biosynthetic pathway of which should involve the participation of a polyketide synthase (PKS). A K. aridum 2.9 kb BamHI genomic fragment homologous to actI (a locus of the PKS cluster catalyzing polyketide chain assembly for actinorhodin biosynthesis in Streptomyces coelicolor) was isolated by shotgun cloning. This DNA fragment, called ardI, was sequenced and the deduced protein products were compared with those of other polyketide synthase genes, revealing similarities ranging from 50 to 80%. ardI was further used to probe a cosmid library of the K. aridum genome. Three hybridizing cosmids were obtained which contain overlapping inserts, together covering a 50 kb region, and including, 15 kb away from ardl, a fragment homologous to actIII, which codes for the ketoreductase of the actinorhodin PKS of S. coelicolor. All these findings indicate that at least part of a polyketide biosynthetic gene cluster has been isolated from the genome of the ardacin producer K. aridum.