Francisella tularensis has been classified as a Category A biodefense agent by the Centers forDisease Control and Prevention because this bacterium is among the most virulent pathogens onthe planet and causes a lethal infection if inhaled. Many pivotal studies in the field havedemonstrated that replication within macrophages during infection is an important feature of thepathogenesis of F. tularensis. My laboratory has furthered the field by showing that interactionswith non-macrophages are also extremely important during infection as these cells provide aniche for immune protection, proliferation, sanctuary from antibiotics, disease transmission, andother unexplored roles. Although much of the work in the field of F. tularensis has focused on therole of macrophages during infection, pathogen interactions with other cell types have not beenthoroughly investigated. We have shown that F. tularensis invades and persists in erythrocytes.This invasion enhances resistance to antibiotics and enhances the ability of this bacterium tocolonize ticks, important disease vectors. Preliminary data suggest that either the erythrocytesurface protein, Band 3, or the cytoskeletal protein, spectrin, are required for invasion. Furtherdata show that a subset of bacterial genes induced in the presence of erythrocytes are importantfor invasion of these host cells. Moreover, structural proteins of the the bacterial type VI secretionsystem (T6SS) are required for invasion, suggesting that this apparatus secretes effectormolecules into erythroctyes to mediate invasion. In this application, we will investigate bacterialgenes induced in the presence of erythrocytes to provide further insight into the mechanism ofred blood cell invasion. We will also identify the T6SS effector molecules that mediate this proces.Finally, we will determine whether Band 3, spectrin, or both host molecules are required for redblood cell invasion by F. tularensis.