Optimization of Culture Conditions for Production of Bioactive Metabolites by Streptomyces spp. Isolated from Soil

The current work was carried out under a screening program targeted at isolation of bioactive Streptomyces species from soil samples. A total of 54 Streptomyces species were isolated from soil samples, out of which 4 isolates were found to be promising. These isolates were identified as Streptomyces spectabilis, Streptomyces purpurascens, Streptomyces coeruleorubidus and Streptomyces lavendofoliae and their sequences have been deposited in the GenBank. The influence of culture conditions including, incubation time, incubation temperature, initial pH and different carbon and nitrogen sources on growth and bioactive compound formation was investigated. Isolate R1, identified as Streptomyces spectabilis, showed maximum bioactive metabolite production with cellobiose and peptone as the carbon and nitrogen sources, on the 5th day at pH 5 at 30℃. The optimum conditions for production by isolate R3, identified as Streptomyces purpurascens, were observed to be starch and casein as the carbon and nitrogen sources, pH 7, temperature 30℃ and an incubation period of eight days. For isolate R5, identified as Streptomyces coeruleorubidus, maximal production resulted on the sixth day at pH 6 and temperature of 35℃ with mannitol and JBM. Isolate Y8, identified as Streptomyces lavendofoliae, was found to produce high levels of bioactive metabolites in the medium supplemented with starch and peptone on the 10th day at pH 7 and at an incubation temperature of 30℃. The four strains tested here behaved differently, each one requiring specific conditions for maximum growth as well as bioactive metabolite production.