Some actinomycete strains isolated from Egyptian soil were screened for their antimicrobial activities using starch casein medium. Two of the actinomycete isolates designated as DN.37 and DN.7 were found to produce a broad spectrum antimicrobial activity. The cultural, physiological, biochemical characteristics and the nucleotide sequence of the 16S rRNA gene of the two isolates strain evidenced a 98 and 99% similarity with Streptomyces cyaneus and Streptomyces lavendulae respectively. The optimum antimicrobial activity occurred upon using medium No. 4 for both isolates. The optimized conditions for antimicrobial productivity were achieved at pH (7.0-7.5); temperature (30oC), agitation speed (200 rpm), working volume (50 ml medium/ 250 ml conical flask) and the best incubation period was 4 and 6 days for both St. cyaneus DN. 37 and St. lavendulae DN. 7 respectively. The optimum inoculums size was 3ml/50ml vegetative cells of 3 days old slant and spore suspension for both St. cyaneus DN. 37 and St. lavendulae DN.7. Both sugar cane molasses and corn steep liquor found to be the best carbon and nitrogen by-product sources for Streptomyces cyaneus DN. 37 while, sugar cane molasses and soybean meal for St. lavendulae DN.7. The suggest optimized medium for the highest antimicrobial productivity in case of St. cyaneus DN. 37 was sugar cane molasses, 70.0; corn steep liquor, 40.0 ml and CaCO3, 2.0, while, for St. lavendulae DN.7 the optimized medium was sugar cane molasses, 60.0; soybean meal, 48.0, and CaCO3, 2.0.
Key words: Streptomyces cyaneus, Streptomyces lavendulae, fermentation, optimization, secondary metabolites
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