Bioactive Secondary Metabolites from Terrestrial Streptomyces baarnensis MH4

Aims: Isolation, screening and identification of potent bioactive compounds producing Streptomyces sp. from the terrestrial soil of Egypt. Fermentation study, product recovery, purification and its characterization was also taken into consideration.
Study Design: Cultivation in lab fermenter, solvent extraction and purification of the compounds by column chromatography, identification of the compounds by mass spectrometry and NMR spectroscopy, determination of the antimicrobial activity.
Place and Duration of Study: Institute of Organic and Biomolecular Chemistry, University of Göttingen, Germany; Department of Microbial Chemistry, National Research Centre, Egypt and Chemistry of Natural Compounds Department, National Research Centre, Egypt, between January, 2009 and December, 2010.
Methodology: The strain was cultivated at 25-liter shaker culture and the fermented broth was filtered and the filtrate was extracted by XAD-16 resin and then by methanol-water, and the concentrated water residue was extracted by ethyl acetate followed by evaporation till dryness. The resultant crude extract was fractionated on silica gel and the components were purified by column chromatography (silica gel, Sephadex column and preparative TLC). The pure component was identified by mass spectrometry (ESI and HRESI-MS), NMR analysis (1H,13C NMR, and 2D NMR) and by comparison with reference data. The antimicrobial activity was determined by disc diffusion assay.
Results: The morphological, biochemical and physiological characterization suggested that isolate MH4 belongs to the genus Streptomyces. Comparison the obtained data with literature data and showed 99% identity coverage towards Streptomyces baarnensis. The scale up fermentation of the isolate MH4 yielded eight known metabolites, nonactic acid (2), homononactic acid (3), 3-(3,3-Di-indolyl)propane-1,2-diol (4), turbomycin A (5), indolyl-3-acetic acid, indolyl-3-carbaldehyde, indolyl-3-carboxylic acid and 2'–deoxyadenosine. Structures of the isolated compounds were assigned by intensive studies of nuclear magnetic resonance (NMR) and mass spectrometry and comparison with corresponding literatures. The taxonomical characterization, fermentation, and biological activity of the Streptomyces baarnensis MH4 were investigated.
Conclusion: The isolate Streptomyces baarnensis MH4 is a potent producer of several antibiotic compounds which can be exploited for their commercial production.