ABSTRACTFrancisella tularensisis a facultative intracellular bacterial pathogen and the causative agent of tularemia. After infection of macrophages, the organism escapes from its phagosome and replicates to high density in the cytosol, but the bacterial factors required for these aspects of virulence are incompletely defined. Here, we describe the isolation and characterization ofFrancisella tularensissubsp.tularensisstrain Schu S4 mutants that lack functionaliglI,iglJ, orpdpC, three genes of theFrancisellapathogenicity island. Our data demonstrate that these mutants were defective for replication in primary human monocyte-derived macrophages and murine J774 cells yet exhibited two distinct phenotypes. TheiglIandiglJmutants were similar to one another, exhibited profound defects in phagosome escape and intracellular growth, and appeared to be trapped in cathepsin D-positive phagolysosomes. Conversely, thepdpCmutant avoided trafficking to lysosomes, phagosome escape was diminished but not ablated, and these organisms replicated in a small subset of infected macrophages. The phenotype of each mutant strain was reversed bytranscomplementation.In vivovirulence was assessed by intranasal infection of BALB/c mice. The mutants appeared avirulent, as all mice survived infection with 108CFUiglJ-orpdpC-deficient bacteria. Nevertheless, thepdpCmutant disseminated to the liver and spleen before being eliminated, whereas theiglJmutant did not. Taken together, our data demonstrate that the pathogenicity island genes tested are essential forF. tularensisSchu S4 virulence and further suggest thatpdpCmay play a unique role in this process, as indicated by its distinct intermediate phenotype.
Whole genome transcriptomics reveals global effects including up-regulation of Francisella pathogenicity island gene expression during active stringent response in the highly virulent Francisella tularensis subsp. tularensis SCHU S4