Characterization of the "pristinamycin supercluster" of Streptomyces pristinaespiralis

Pristinamycin, produced by Streptomyces pristinaespiralis Pr11, is a streptogramin antibiotic consisting of two chemically unrelated compounds, pristinamycin I and pristinamycin II. The semi-synthetic derivatives of these compounds are used in human medicine as therapeutic agents against methicillin-resistant Staphylococcus aureus strains. Only the partial sequence of the pristinamycin biosynthetic gene cluster has been previously reported. To complete the sequence, overlapping cosmids were isolated from a S. pristinaespiralis Pr11 gene library and sequenced. The boundaries of the cluster were deduced, limiting the cluster size to approximately 210 kb. In the central region of the cluster, previously unknown pristinamycin biosynthetic genes were identified. Combining the current and previously identified sequence information, we propose that all essential pristinamycin biosynthetic genes are included in the 210 kb region. A pristinamycin biosynthetic pathway was established. Furthermore, the pristinamycin gene cluster was found to be interspersed by a cryptic secondary metabolite cluster, which probably codes for a glycosylated aromatic polyketide. Gene inactivation experiments revealed that this cluster has no influence on pristinamycin production. Overall, this work provides new insights into pristinamycin biosynthesis and the unique genetic organization of the pristinamycin gene region, which is the largest antibiotic 'supercluster' known so far