Biosynthesis in Streptomyces sp. NRRL S-1813 and regulation between oxazolomycin A and A2

A novel actinomycete strain, Streptomyces sp. NRRL S-1813 was employed to study its secondary metabolites under different mediums to activate its cryptic gene clusters and produce antimicrobial secondary metabolites. During fermentation optimization, and purification, oxazolomycin A and oxazolomycin A2 were isolated from one strain simultaneously. Their structure was elucidated using a series of characterization techniques, including full wavelength scanning, mass spectrometry (MS), and nuclear magnetic resonance (NMR) spectroscopy. Oxazolomycin A2 was found not to be a typical enzymatic product of fermentation process. Instead, a spontaneous, non-enzymatic ring cleavage reaction was identified as mechanism for conversion of oxazolomycin A to oxazolomycin A2. Basing on these results, if the target product is oxazolomycin A2, the best fermentation condition of Streptomyces sp. NRRL S-1813 should be the Medium B under the alkalescence condition. For the biosynthesis of oxazolomycin A, the medium pH and reaction time were both important. A slightly acidic environment suppresses the side reactions such as hydrolysis of product, while reasonable reaction time minimizes accumulation of byproducts.