Multiple peptide synthetase gene clusters in Actinomycetes
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O R I GI N A L P A P E R
M. Sosio á E. Bossi á A. Bianchi á S. Donadio
Multiple peptide synthetase gene clusters in Actinomycetes
Received: 8 March 2000 / Accepted: 8 July 2000 / Published online: 1 September 2000 Ó Springer-Verlag 2000
Abstract Two oligonucleotide probes derived from conserved motifs in peptide synthetases were hybridized with a cosmid library of Planobispora rosea genomic DNA. Detailed characterization of the physical organization of the positive cosmids indicated the existence of at least eight unlinked contigs containing multiple fragments that hybridized to both probes. Partial sequences of PCR products from the positive cosmids con®rmed the existence of peptide synthetase genes. The combined results of hybridizations and physical mapping indicate that, in all likelihood, the isolated P. rosea contigs encode over 40 putative peptide synthetase modules. Similar results were obtained on screening a cosmid library of Actinoplanes teichomyceticus DNA. Furthermore, Southern hybridizations with several actinomycete strains, belonging to dierent genera, indicate that most strains contain multiple hybridizing bands ± well in excess of the number expected from the structure of the oligopeptides produced by these strains. Even strains not reported to produce oligopeptides gave clear positive signals when examined with the probes. These results strongly suggest that actinomycetes devote a notable fraction of their genomes to the non-ribosomal synthesis of peptides, and that most strains have the genetic potential to produce more oligopeptides than are currently described. Key words Antibiotics á Modular systems á Secondary metabolites á Streptomyces
Communicated by W. Arber M. Sosio á E. Bossi á A. Bianchi á S. Donadio (&) Biosearch Italia SpA, Via R. Lepetit 34, 21040 Gerenzano, Italy E-mail: [email protected] Tel.: +39-2-96474243 Fax: +39-2-96474238
Introduction Over 60% of the known microbial metabolites are produced by members of the order Actinomycetales, and the genus Streptomyces is reported as the most proli®c producer of secondary metabolites. Because Streptomyces strains are easy to isolate and are good producers of secondary metabolites, over the past several decades many laboratories have conducted a vast screening eort to isolate secondary metabolites with interesting biological activities. In view of the large number of streptomycetes isolated and screened, the chances of ®nding known metabolites when newly isolated streptomycetes are screened has increased (Lancini and Lorenzetti 1993). Many strains belonging to unusual genera of actinomycetes have also been isolated in the hope that they might produce novel chemical structures not previously identi®ed in streptomycetes. However, simple tests (i.e. for antimicrobial activity) indicate that Streptomyces strains produce bioactivities more frequently than most other genera of actinomycetes (such as Actinoplanes and Streptosporangium; G. Lancini, personal communication). It is not currently known if the higher frequency of antibiotic
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