A Francisella tularensis pathogenicity island protein essential for bacterial proliferation within the host cell cytosol

Abstract

SummaryFrancisella tularensis is an intracellular bacterial pathogen, and is a category A bioterrorism agent. Within quiescent human macrophages, the F. tularensis pathogenicity island (FPI) is essential for bacterial growth within quiescent macrophages. The F. tularensis-containing phagosome matures to a late endosome-like stage that does not fuse to lysosomes for 1-8 h, followed by gradual bacterial escape into the macrophage cytosol. Here we show that the FPI protein IglD is essential for intracellular replication in primary human monocyte-derived macrophages (hMDMs). While the parental strain replicates robustly in pulmonary, hepatic and splenic tissues of BALB/c mice associated with severe immunopathologies, the isogenic iglD mutant is severely defective. Within hMDMs, the iglD mutant-containing phagosomes mature to either a late endosome-like phagosome, similar to the parental strain, or to a phagolysosome, similar to phagosomes harbouring the iglC mutant control. Despite heterogeneity and alterations in phagosome biogenesis, the iglD mutant bacteria escape into the cytosol faster than the parental strain within hMDMs and pulmonary cells of BALB/c mice. Co-infections of hMDMs with the wild-type strain and the iglD mutant, or super-infection of iglD mutantinfected hMDMs with the wild-type strain show that the mutant strain replicates robustly within the cytosol of hMDMs coinhabited by the wild strain. However, when the wild-type strain-infected hMDMs are super-infected by the iglD mutant, the mutant fails to replicate in the cytosol of communal macrophages. This is the first demonstration of a F. tularensis novel protein essential for proliferation in the macrophage cytosol. Our data indicate that F. tularensis transduces signals to the macrophage cytosol to remodel it into a proliferative niche, and IglD is essential for transduction of these signals.

MglA and Igl Proteins Contribute to the Modulation ofFrancisella tularensisLive Vaccine Strain-Containing Phagosomes in Murine Macrophages

“…Thus, the igl mutants were capable of intracellular replication, albeit at a rate lower than that of F. tularensis LVS. These results are in agreement with our previous findings concerning (16,21,28,29). Macrophages activated with IFN-␥ were capable of restricting the replication of all strains; the number of LVS bacteria decreased by 0.7 log 10 , the numbers of ⌬iglC and ⌬iglD bacteria decreased by 2.3 and 2.0 log 10 , respectively, and the ⌬mglA strain was completely eliminated during the 72 h of incubation (Fig.…”

The bacterial type VI secretion machine: yet another player for protein transport across membranes

“…The iglD gene encodes a protein with some similarities to ImpJ, particularly in the N-terminal domain. The iglD gene is essential for intracellular replication in primary human monocyte-derived macrophages (Santic et al, 2007). Other genes, iglC, pigC and pigG, seem to be unique to Francisella.…”

Nooks and Crannies in Type VI Secretion Regulation

“…Several phenotypes have been correlated with T6SS function: virulence of Burkholderia cenocepacia toward mice, survival of Burkholderia mallei and Aeromonas hydrophila in macrophages, resistance of Vibrio cholerae to amoeba predation, Rhizobium leguminosarum symbiosis, biofilm formation by enteroaggregative Escherichia coli, intracellular growth of Francisella tularensis and Salmonella enterica in macrophages, and stress sensing in Vibrio anguillarum (3,11,53,62,82,87,94,95,101,111). In most cases for Gram-negative pathogens, T6SS are not critical determinants of pathogenesis but rather improve the efficiency of several stages during colonization and/or infection.…”