Healthcare-associated infections (HAIs) pose a tremendous threat to the personal and financial wellbeing of the American people. Over the last decade, there has been a surge in mortality due to HAIs as a result of several compounding factors (e.g., increased levels of drug resistance among microbes, escalating numbers of immunocompromised patients, and a sharp decline in the production of new antimicrobials). Consequently, there is a critical need for the development of new antifungal and antibacterial therapeutics to stem the loss of human life caused by HAIs. Unfortunately, many modern drug screening programs rely on chemically impoverished libraries that severely compromise their respective lead discovery potentials. A major shortcoming for many of these chemical libraries is the significant degree of compound homogeneity and a lack of structural novelty among their component compounds. The objective of this application is to use a chemical-epigenetics methodology to critically examine the unique secondary metabolites that are encoded by silent biosynthetic pathways in fungi as a source of novel antimicrobials. We will test the central hypothesis that the activation of silent natural-product gene clusters in fungi will provide unparalleled access to chemically diverse secondary metabolites, which we will use for procuring new antibacterial and antifungal leads. The rationale for investigating silent biosynthetic pathways for the production of antimicrobials is that secondary metabolites emerging from this source are expected to be structurally and functionally novel; thus these compounds are anticipated to have significant drug development value. Based on our research group's strong preliminary data, three specific aims have been designed to test the central hypothesis: 1) investigate the range of antimicrobial activities emerging from fungi following chemical-epigenetic modification, 2) use bioassay-guided microplate fractionation in tandem with electrospray-ionization time-of-flight mass spectrometry to dereplicate and purify bioactive natural products for testing against a panel of microbial pathogens, and 3) apply a combination of biosystematic and semisynthetic techniques to probe the structure- activity features of two unique groups of antimicrobial leads previously discovered in the PI's laboratory. This research is significant because it capitalizes on an innovative methodology, chemical epigenetics, to access cryptic natural products from fungi. These compounds represent an untapped source of bioactive organic molecules with outstanding therapeutic applications. It is anticipated that these studies will provide an array of chemically unprecedented natural products that will have superb lead development potential as part of future NIH-sponsored studies.