PROJECT SUMMARY Persistent colonization is a key facet of microbe-host interactions. Little is knownabout the mechanisms that allow a bacterium to persistently colonize its host. We havedeveloped a mouse model for dissecting bacterial and host determinants of persistentcolonization. It pairs a commensal of wild mice Neisseria musculi with the lab mousewhich is not naturally colonized with Neisseria. N. musculi is closely related tocommensal and pathogenic species of Neisseria and encode many host interactionfactors and vaccine candidates of these pathogens. A single oral dose of N. musculiresults in persistent asymptomatic colonization of the oral cavity and gut of the mousefor at least 1 year. Colonization requires not only the Type IV pilus (Tfp) fiber but alsoretraction of the fiber. pilE which does not express the pilus fiber subunit and pilTwhich does not express the pilus retraction motor both fail to colonize mice. Here wewill use our newly developed model to examine the role of Tfp retraction on N. musculicolonization and persistence. We will also use spectral imaging Fluorescence In SituHybridization (FISH) to locate and characterize the biofilms formed by N. musculi and itsTfp retraction mutant in the mouse alimentary tract.