Discovery and biosynthesis of novel natural products from Streptomyces venezuelae

Doctoral thesis English OPEN
Sidda, John David
  • Subject: QD | QR

Streptomyces bacteria are prolific producers of secondary metabolites. These natural products find uses ranging from antibiotics and antifungals to immunomodulatory agents and pesticides. Biosynthesis of secondary metabolites is often tightly controlled; therefore novel strategies for activation of cryptic secondary metabolites are required.\ud \ud The metabolites of the Streptomyces venezuelae wild type and a mutant strain lacking the ArpA-like transcriptional repressor GbnR have been compared, leading to the identification of the gaburedins – novel, ureido-linked dipeptides – in the gbnR mutant. A combination of in vivo precursor-directed studies has led to a proposed biosynthetic route to gaburedins. Metabolic profiling of a range of other mutant strains has identified gbnB as an essential gene in the gbnABC gene cluster that is responsible for gaburedin biosynthesis. Synthesis of an authentic standard of gaburedin A combined with chiral HPLC analysis of culture extracts has allowed the proposed structure of gaburedins to be confirmed. Bioinformatic analyses of the gbnABC cluster responsible for gaburedin biosynthesis have revealed orthologous systems in a range of other bacterial genera and efforts to reconstitute the S. venezuelae gbnABC pathway in E. coli have begun.\ud \ud The regulatory mechanism controlling gaburedin biosynthesis in S. venezuelae has also been investigated, leading to the discovery of new AHFCA signalling molecules which have been shown to induce gaburedin biosynthesis in a mutant strain unable to produce AHFCAs. This work demonstrates for the first time that AHFCA signalling is involved in regulation of other natural products as well as the methylenomycin cluster from which AHFCAs were first identified.\ud \ud Gaburedins represent the first example by which deletion of an arpA-like regulatory gene has been used as a strategy for de-repression of a biosynthetic pathway for cryptic natural product biosynthesis. The current project demonstrates that rational deletion of proposed regulatory genes is a powerful approach to natural product discovery.\ud
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