Isolation and Characterization of Streptomyces sp. ANBS-15 and Antimicrobial Activities of its Secondary Metabolites

A total of 15 actinomycetes were isolated and purified from soil samples collected from agricultural fields of Rajshahi University, Bangladesh. The isolates were morphologically distinct on the basis of spore mass color, reverse slide color, aerial and substrate mycelia formation and production of diffusible pigment. The strain ANBS- 15 was selected for further investigation due to its strong antibacterial and antifungal activity and was identified as a member of Streptomyces genus based on its morphological, cultural, physiological, utilization of carbon sources and biochemical characteristics. From Czapek-dox broth fermentation medium of this strain, two active compounds, namely as MB-1a and MB-1b, were separated and purified. The compounds showed moderate to high antibacterial and antifungal activities. The antibacterial activity was in the range of 9-22 mm against 8 gram- positive and 2 gram-negative bacteria. The activity of MB-1a was higher than MB-1b against gram-positive bacteria. The antifungal activities of MB-1a and MB-1b against Candida albicans, Aspergillus niger, Aspergillus ocherus and Aspergillus ustus were in the range of 10-17 mm using 50 µg/disc. The results indicate that the soil of Bangladesh is rich source of actinomycetes having antibacterial and antifungal activities. Thus, there is potential of discovery of novel bioactive metabolites.