Isolation of membrane-active fraction of Streptomyces spp. from soil
Purpose: To isolate and characterize the membrane-active antimicrobial fraction and isolate metabolite produced by Streptomyces in soil samples from Iran
Methods: More than 60 Actinomycete strains were isolated from soil samples in Iran. A total number of 16 strains were studied using antimicrobial assay against Escherichia coli, Candida albicans and Staphylococcus aureus. Among these, three strains produced membrane-active metabolites based on artificial vesicle assay. Extracts of Streptomyces culture were obtained using ethyl acetate fractionation.
Antimicrobial activity was evaluated by broth microdilution assay. Among these active extracts, one metabolite was isolated. Further fractionation and purification strategies were applied to finally identify the isolated metabolite using appropriate spectroscopic methods including thin layer chromatography (TLC), preparative thin-layer chromatography (PTLC), high performance liquid chromatography (HPLC),
nuclear magnetic resonance (NMR) and liquid chromatography–mass spectrometry (LC-MS).
Results: Three strains isolated from the soil samples, namely, strains 0811, 08346 and 08317 showed the highest antifungal and antimicrobial activity in Tryptic Soy Broth (TSB) and International Streptomyces Projects 2 (ISP2) medium in the range of 46.8 to 62.5 μg/ml. Strain 08346 was selected for further chemical profiling based on TLC pattern and membrane activity. It yielded a purified compound which was determined to be a novel aromatic amino alkyne, named Sourin.
Conclusion: Streptomyces-produced 08346 strain demonstrates good antimicrobial activities against bacteria and yeasts, suggesting its potential as an antimicrobial membrane-active agent.
Keywords: Actinomycetes, Secondary metabolites, Streptomycetes, Membrane-active agent