Antimicrobial secondary metabolite-producing potential of streptomyces sp. isolated from soil

A total of 150 strains of actinomycetes were isolated from different soil samples collected from various locations of Patna (Bihar). The actinomycetes strains were screened for their antimicrobial potential against test organisms such as Escherichia coli MTCC 739, Staphylococcus aureus MTCC 96, Streptomyces lividans TK 23 MTCC 4, and Candida albicans MTCC 227 by cross-streak method. The bioassay revealed that about 53.33% of actinomycetes isolates were active against test organisms. Characterization of these isolates has led to identification of unique strains of Streptomyces (MP 562 and NP 302) showing broad spectrum of antimicrobial properties. On the basis of λmax values of culture filtrates, it has been suggested that these strains might be producing LL-E19085 and lipopeptide LY146032 like antibacterial and a flavone glycoside like antifungal antibiotics.

According to Bergey's Manual of Determinative Bacteriology, the strains MP 562 and NP 302 have been identified as Streptomyces clavuligerus MTCC 8722 and Streptomyces anulatus US7 MTCC 8724, respectively. Starch casein broth was found to be the best medium for the growth as well as antibiotic production for both strains. Maximum antimicrobial secondary metabolites production was achieved in late log phase which remained constant during stationary phase. The pH and temperature optima of antibiotics production have been found to be in the range of 6.5 to 7.0 and 30° C to 35° C, respectively.