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

Abstract

TheFrancisella tularensislive vaccine strain (LVS), in contrast to itsiglCmutant, replicates in the cytoplasm of macrophages. We studied the outcome of infection of the murine macrophagelike cell line J774A.1 with LVS and withiglC,iglD, andmglAmutants, the latter of which is deficient in a global regulator. Compared to LVS, all of the mutants showed impaired intracellular replication up to 72 h, and the number of themglAmutant bacteria even decreased. Colocalization with LAMP-1 was significantly increased for all mutants compared to LVS, indicating an impaired ability to escape into the cytoplasm. A lysosomal acidity-dependent dye accumulated in approximately 40% of the vacuoles containing mutant bacteria but not at all in vacuoles containing LVS. Preactivation of the macrophages with gamma interferon inhibited the intracellular growth of all strains and significantly increased acidification of phagosomes containing the mutants, but it only slightly increased the LAMP-1 colocalization. The intracellular replication and phagosomal escape of theiglCandiglDmutants were restored by complementation intrans. In conclusion, the IglC, IglD, and MglA proteins each directly or indirectly critically contribute to the virulence ofF. tularensisLVS, including its intracellular replication, cytoplasmic escape, and inhibition of acidification of the phagosomes.