NEW METHODS FOR MICROBIAL NATURAL PRODUCT DISCOVERY AND STRUCTURE ELUCIDATION

Abstract

Natural product discovery is a vital area of research, providing invaluable insights into the development of new therapeutics and the understanding of complex ecological interactions. This thesis presents the integration of traditional and modern approaches in natural product discovery, demonstrating their successful application in uncovering novel compounds with potential therapeutic and ecological significance across three distinct studies. Each chapter uniquely addresses common challenges in the natural product discovery field using a variety of methods. Chapter 2 explores the use of phenotype-guided transposon mutagenesis in Burkholderia thailandensis to activate a silent biosynthetic gene cluster. By employing random transposon mutagenesis and phenotypic inspection, several mutants with enhanced expression of an iterative type I polyketide synthase cluster, termed org, were identified. The resulting metabolites, thailandene A-C, displayed potent antibiotic activity against Staphylococcus aureus and Saccharomyces cerevisiae, highlighting the potential of this approach in identifying bioactive compounds. Chapter 3 reports the discovery of novel cryptic polyamides from Thermosporothrix hazakensis using MS-guided High-throughput Elicitor Screening (HiTES). Exposure to an elicitor library and monitoring natural product biosynthesis via HPLC-MS led to the identification of a group of novel compounds, called hazakemides. These polyamides, derived in part from aliphatic amino acids, exhibited antimicrobial and anticancer activities. The synthesis of hazakemides is also reported to verify their absolute configurational assignments. In Chapter 4, eight architecturally unusual secondary metabolites synthesized by the bacterial symbiont Phaeobacter inhibens, using precursors provided by algal hosts, were uncovered. These metabolites, identified via microcrystal electron diffraction, exhibited potent algaecidal activity, suggesting that bacterial symbionts can convert algal precursors, such as tryptophan and sinapic acid, into complex cytotoxins. This finding has crucial implications for understanding the parasitic phase of algal-bacterial symbiotic interactions. Together, this thesis presents a diverse array of methods and novel compounds in natural product discovery and demonstrates their successful application in characterizing new compounds with therapeutic and ecological relevance. The discoveries presented here contribute to our understanding of natural product biosynthesis, microbial interactions, and their potentials for developing new therapeutics.