Identification of a gene cluster for antibacterial polyketide-derived antibiotic biosynthesis in the nystatin producer Streptomyces noursei ATCC 11455

Streptomyces noursei ATCC 11455 produces the antifungal polyene antibiotic nystatin containing the deoxysugar moiety mycosamine. Part of the deoxythym idyl diphosphate (TDP)-glucose dehydratase gene (gdhA) known to be involved in deoxysugar biosynthesis was amplified by PCR from genomic DNA of S, nou rsei ATCC 11455, A gene library for S, noursei was made and screened with t he gdhA probe. Several overlapping phage clones covering about 30 kb of the S, noursei genome were physically mapped, A partial DNA sequencing analysi s of this region resulted in the identification of several putative genes t ypical of macrolide antibiotic biosynthetic gene clusters, A gene-transfer system for S, noursei has been established, and gene deletion or disruption experiments within the putative biosynthetic gene cluster were performed, All of the knock-out mutants retained the ability to produce nystatin, sugg esting that the identified gene cluster is not involved in biosynthesis of this antibiotic. Culture extracts from the wild-type strain and three knock -out mutants were analysed by TLC followed by a bioassay against Micrococcu s luteus. Two antibacterial compounds were found to be synthesized by the w ild-type strain while only one was produced by the mutants, This provided e vidence for the involvement of the identified gene cluster in the biosynthe sis of a presumably novel antibacterial macrolide antibiotic in S, noursei.