Isolation, identification and optimization of fermentation parameters for improved production of antimicrobial compounds from indigenous Streptomyces isolates

Abstract

In order to find out new antimicrobial compounds producing Stretomycetes from indigneous soil, twenty five Streptomyces isolates were purified from hundred soil samples and screened for their antimicrobial potential. Among these isolates, four (SK-1, SK-3, SK-4 and SK-5) were selected for further studies on the basis of antimicrobial compounds produced by them. Morphological, cultural, physiological and biochemical characterization revealed that these isolates belonged to the Streptomyces species. Moreover, 16S ribosomal RNA gene analysis confirmed that these isolates showed 99% identity to Streptomyces variabilis, Streptomyces flavomacrosporus, Streptomyces levis and Streptomyces griseostramineus, respectively. The antimicrobial compounds produced by SK-1, SK-3 and SK-4 isolates exhibited strong antibacterial activities against Bacillus subtilis, Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa and Rhodococcus facians. While, isolate SK-5 showed strong antifungal activities against Trichoderma and Aspergillus species. The optimum inoculum size (v/v %), temperature and pH for antimicrobial metabolite production by Streptomyces isolates (SK-1, SK-3, SK-4 and SK-5) were found to be 10%, 28-34°C and 8.0-9.0, respectively. Casein starch medium supplemented with 1% starch and 0.2% sodium glutamate proved to be the best carbon and nitrogen sources for the production of antibacterial compounds by isolates SK-1, SK-3 and SK-4. While isolate SK-5 gave maximum antifungal activities when 1% glycerol was used in the fermentation medium along with 0.2% tryptone as nitrogen source.