PROJECT SUMMARYEnteric bacterial infections remain one of the greatest public health challenges worldwide and deciphering themechanisms that protect against infection will enable development of new treatments. Intestinal tissues are inconstant direct contact with diverse beneficial and pathogenic microbes, highlighting the need for orchestratingcomplex microbial signals to sustain protection against infection. Intestinal epithelial cells (IECs) reside at thedirect interface between intestinal pathogens, beneficial commensal bacteria, and intestinal immunecomponents. However, despite continuous exposure to diverse microbes, the mechanisms regulating howIECs integrate microbial-derived signals to mount protective host responses to pathogens are not wellunderstood. Epigenetic changes represent a powerful interface that enable cells to respond to environmentalsignals and modify gene expression. The goals of this proposal are to interrogate how specific commensalbacterial-derived metabolites that regulate the epigenetic-modifying enzyme histone deacetylase 3 (HDAC3)influence intestinal protection against infection and bacterial translocation. Employing Citrobacter rodentium, amurine model of human enteropathogenic Escherichia coli infection, our studies identified that HDAC3 protectsagainst enteric bacterial infection. New preliminary data suggest commensal bacterial-derived metabolites candirectly modulate HDAC3 function in IECs and that distinct types of commensal bacteria establish uniquehistone acetylation signatures in IECs. Collectively, these data suggest that HDAC3 senses distinct metabolitesignals derived from commensal bacteria to epigenetically prime host defense against pathogenic bacterialinfection. Employing an exciting array of transgenic animals, pathogenic and commensal bacterial strains, andhuman intestinal organoids, three specific aims are proposed that will (i) investigate metabolite-dependentregulation of enteric infection, (ii) decipher how the host calibrates intestinal barrier function by sensing distinctcommensal bacterial-derived metabolites, and (iii) interrogate whether distinct types of commensal bacteriaprime the epigenome to enhance host response to pathogenic bacteria. Defining pathways that integratecommensal and pathogenic signals will provide a framework to test the therapeutic potential of manipulatingcommensal bacterial-derived metabolites to promote antibacterial immunity.