Isolation and characterization of bioactive secondary metabolites from selected Streptomyces strains

Actinomycetes are Gram-positive soil bacteria known as producers of secondary bioactive metabolites. In the search for new bioactive compounds collection of actinomycetes from the Laboratory for Microbial Molecular Genetics and Ecology (Institute of Molecular Genetic and Genetic Engineering, University of Belgrade) was screened according to several criteria - bioactivity, the presence of the genes for polyketide synthase (PKS), pigmentation, and crude culture extracts absorption profile in ultraviolet and visible (UV/Vis) spectra. Based on these we have isolated three strains NP10, JS520, and Streptomyces durmitotensis, previously renewed for didehydroroflamicoin (DDHR) production. Isolates NP10 and JS520 were identified to belong to the genus Streptomyces. Streptomyces sp. NP10 accumulated branched chain fatty acids, predominately isopalmitic, and cyclic dipeptides consisting of proline in combination with valine, isoleucine or alanine, that have a stimulating effect on the trophoblast cell line in culture at low concentrations (1 ng/ml and 1 mg/ml) and cytotoxic effect at high concentrations (1 mg/ml). Streptomyces sp. JS520 was determined to be exceptionally good producer of pigment undecylprodigiosine (UP) with antibacterial, antifungal, antioxidant and UV protective activities showing cytotoxic effects on trophoblast cell line in culture at high concentrations (1 ng/ml). Cytotoxicity of polyene macrolide antibiotic DDHR from S. durmitotensis was confirmed and it’s antifungal effects were shown. PKS cluster responsible for DDHR synthesis was subcloned in the cosmid library and partially sequenced. Optimization of culture conditions resulted in 2.12 times increased production of UP, and 1.1 times increased production of DDHR