Screening of secondary metabolite biosynthesis genes from terrestrial streptomyces strains

Microbial secondary metabolites represent a large source of compounds endowed with ingenious structures and potent biological activites. Streptomyces strains which are belonging to the order Actinomycetales are superior to other actinomycete strains in their abilitiy to produce large numbers and varietes of bioactive metabolites. The main compounds of these secondary metabolites are antibacterial, antifungal and antitumour agents. To explore new bioactive secondary metabolites, the main strategy is to search for new compounds from well known and talented microorganisms such as Streptomyces. The dedection of gene sequences involved in the synthesis of secondary metabolites to evaluate the biosynthetic potential has already been described in different taxonomic groups and actinomycetes. This approach may represent an alternative way to focus the screening on wild-type isolates with the highest metabolic potential. Nonribosomal peptide sythetases (NRPS) and poliketide synthases (PKS) are biosynthetic systems involved in the synthesis of large number of important biologically active compounds produced by actinomycetes .In our study, it was used that 15 Streptomyces strain which were previously isolated rhizospheric soils of some Turkish endemic plants and characterized by molecular methods. Our aim was to screen the NRPS and PKS-I genes in the genom of these local strains by PCR approach. It was determined that all 15 strain have NRPS and PKS-I genes. PCR amplicons of NRPS genes from Streptomyces sp BSH50 and PKS-I genes from Streptomyces sp AS29 were cloned to constitute mini libraries. Sequence analysis of selected clones from the libraries were compared to the published sequences by using BLAST software in the NCBI (National Center for Biotechnology Information) GenBank. According to our results, Streptomyces sp BSH50 has 11 different A domains those are belong to NRPS genes. These domains have homology between 45 - 95 % with the other genes published in GenBank. It was found that Streptomyces sp AS29 has 3 different KS domains for PKS-I genes. The PKS-I genes of this isolate have homology between 61 - 72 % when compared to other published PKS-I genes. In future work, pütative new domains will be used as homolog probes in hybridization experiments to reach new biosynthetic gene clusters in the genome of isolates.