Analysis of secondary metabolites from Streptomyces venezuelae VS1099

Jadomycin and jadomycin B are antibiotic and cytotoxic secondary metabolites produced by Streptomyces venezuelae cultures exposed to nutritional stress and ethanol toxicity. These pigmented compounds are composed of an angucycline framework and a unique oxazolone ring originating from Ile, the sole nitrogen source in the culture medium. The aims of the project were to improve the yields of jadomycin and jadomycin B, to isolate potential jadomycin analogues and other secondary metabolites of interest by substituting Ile with equimolar concentrations of alternative amino acids, and to investigate the structures of the isolated secondary metabolites. By using the regulatory mutant strain VS1099, a nutrient medium containing 10 mM MOPS buffer and 66 mM Ile, as well as using ethanol shock when the culture growth reached OD 600 ≈ 0.5, product yields were increased. From small-scale growth experiments in which cultures were separately fed D-Ile, D-Val or one of the 20 protein amino acids, jadomycin B analogues were identified in the crude extracts by electrospray tandem mass spectrometry. From large-scale growth experiments using DL-Ile, DL -Val or D-Val as the sole nitrogen source, modified jadomycins bearing an oxazolone ring originating from the specific amino acid fed were isolated and partially characterized using nuclear magnetic resonance spectroscopy, whereas pigmented secondary metabolites with structures different from jadomycins were isolated from cultures fed Trp, Lys or Ala, and also partially-characterized by nuclear magnetic resonance spectroscopy.