Updated project metadata. Metabolic adaptation has recently been recognized as a key component of the intracellular life cycle of pathogenic microorganisms. Upon entry into mammalian host cells, Francisella tularensis, a pathogenic bacterium responsible for the zoonotic disease tularemia, rapidly escapes from the phagosome to multiply actively in the cytosolic compartment. Francisella is auxotroph for several amino acids, including arginine, and thus relies exclusively on their import from the host to survive in infected cells. We identified an arginine transporter (hereafter designated ArgP) whose inactivation considerably delayed bacterial phagosomal escape and intracellular multiplication. Remarkably, this defect could be totally suppressed in macrophages and dendritic cells from IRAP-KO mice. Wild-type cytosolic multiplication of the mutant bacteria was restored in these cells, indicating that the ArgP transporter is mainly required for arginine uptake in the phagosomal compartment. Proteomic analyses showed that arginine deprivation in the ∆argP mutant rapidly affected the expression of a numerous proteins, and in particular reduced expression of most of the ribosomal proteins. We propose that regulation of ribosomal protein biogenesis may contribute to the sensing of the intracellular stage of the pathogen and to phagosomal membrane disruption.