New PCR primers for the screening of NRPS and PKS-I systems in actinomycetes: detection and distribution of these biosynthetic gene sequences in major taxonomic groups.

Nonribosomal peptide synthetases (NRPS) and type I polyketide synthases (PKS-I) are biosynthetic systems involved in the synthesis of a large number of important biologically active compounds produced by microorganisms, among others by actinomycetes. In order to assess the occurrence of these biosynthetic systems in this metabolically active bacterial group, we designed new PCR primers targeted to specifically amplify NRPS and PKS-I gene sequences from actinomycetes. The sequence analysis of amplified products cloned from two model systems and used to validate these molecular tools has shown the extreme richness of NRPS or PKS-I-like sequences in the actinomycete genome. When these PCR primers were tested on a large collection of 210 reference strains encompassing all major families and genera in actinomycetes, we observed that the wide distribution of these genes in the well-known productive Streptomyces species is also extended to other minor lineages where in some cases very few bioactive compounds have been identified to date.