BIOSYNTHESIS OF DITHIOLOPYRROLONE NATURAL PRODUCTS AND DISCOVERY OF ANTIBIOTIC COMBINATIONS

Bacteria produce a wide variety of natural products with diverse structures and bioactivities. These compounds are valuable sources for pharmaceuticals, and their biosynthetic enzymes can be repurposed as biocatalysts for challenging syntheses. Chapter 1 provides an overview of how sulfur and selenium are incorporated into natural products. Chapter 2 describes the identification and characterization of a methyltransferase for dithiolopyrrolones, a class of sulfur-containing natural products with broad-spectrum antimicrobial activities. This methyltransferase accepts many dithiopyrrolone substrates and expands the limited examples of amide N-methyltransferases. In Chapter 3, inspired by the broad-spectrum antimicrobial activity of thiomarinol A, a hybrid of dithiolopyrrolone and a relatively narrow-spectrum antibiotic mupirocin, I synthesized a hybrid of dithiolopyrrolone and linezolid to test if conjugation with dithiolopyrrolone could expand the antimicrobial spectrum of linezolid. In Chapter 4, I turned to identify synergistic antimicrobial combinations, i.e., two natural products that are more effective when used together. Because many synergistic combinations are natural products encoded by co-localized biosynthetic gene clusters (BGCs), I searched for co-localized BGCs, predicted the combinations of natural products made by these BGCs, and investigated the mode of action of one combination. Finally, in Chapter 5, I investigated an unknown BGC in Pseudomonas aeruginosa, a pathogenic bacterium. Comparative metabolomics and in vitro enzymatic assays were performed to identify the natural product made by enzymes encoded by this BGC.