The C‐terminus of IcmT is essential for pore formation and for intracellular trafficking of Legionella pneumophila within Acanthamoeba polyphaga

Abstract

The C-terminus of IcmT is essential for pore formation and for intracellular trafficking of Legionella pneumophila within Acanthamoeba polyphaga respectively, in intracellular growth in A. polyphaga, and the respective defects correlated with fusion of the bacterial phagosomes to lysosomes. Taken together, the data showed that the C-terminus domain of IcmT is essential for the pore-forming activity and is required for intracellular trafficking and replication within A. polyphaga, but not within mammalian cells. IntroductionLegionella pneumophila, the bacterium responsible for the acute pneumonia designated Legionnaire's disease, is able to grow within cells in the alveolar spaces . In the environment, this bacterium replicates within protozoa (Rowbotham, 1980;1986). Intracellular replication is culminated in pore formationmediated cytolysis of the protozoan host and subsequent bacterial egress (Gao and Abu Kwaik, 2000a). At least 15 species of protozoa support the intracellular growth of L. pneumophila, and bacterial replication within amoebae plays a major role in bacterial ecology and pathogenesis .Infection of both mammalian and protozoan cells by L. pneumophila shares similar mechanisms (Gao et al., 1997;. After entry into both host cells, L pneumophila modulates the biogenesis of the vacuole into a replicative niche, which does not fuse to lysosomal compartments and is subsequently surrounded by mitochondria and the rough endoplasmic reticulum Abu Kwaik et al., 1998a). The type IV Dot/Icm secretion system is essential for evasion of lysosomal fusion Vogel et al., 1998). After termination of intracellular replication, L. pneumophila induces expression of the pore-forming toxin, which is essential for cytolysis of the host cell and subsequent bacterial egress (Byrne and Swanson, 1998;Alli et al., 2000). Egress from host cells is a fundamental step in the life cycle of intracellular pathogens that allows the organism to spread to a new susceptible host cell and to search for a new replication niche.Mutants defective in egress from the host cell upon termination of intracellular replication have been isolated in our laboratory and designated rib (release of intracellular bacteria) (Alli et al., 2000;Gao and Abu Kwaik, 2000a SummaryWe have shown previously that the five rib (release of intracellular bacteria) mutants of Legionella pneumophila are competent for intracellular replication but defective in pore formation-mediated cytolysis and egress from protozoan and mammalian cells. The rib phenotype results from a point mutation (deletion) DG 544 in icmT that is predicted to result in the expression of a protein truncated by 32 amino acids from the C-terminus. In contrast to the rib mutants that are capable of intracellular replication, an icmT null mutant was completely defective in intracellular replication within mammalian and protozoan cells, in addition to its defect in pore formation-mediated cytolysis. The icmT wild-type allele complemented the icmT null mutant for both defects of intracellular replicati...

Identification ofMycobacterium aviumpathogenicity island important for macrophage and amoeba infection

“…Other pathogens, like Legionella pneumophila, also infect amoeba in the environment (17). Genes required for Legionella to survive within macrophages are quite similar to the ones required to live inside amoeba (18), indicating the ability to infect and survive in protozoa might have adapted Legionella to the mammalian cell environment.…”

IcmR-regulated Membrane Insertion and Efflux by the Legionella pneumophila IcmQ Protein

“…In contrast with this hypothesis, however, a partial loss of function mutation in icmT depresses high multiplicity of infection cytotoxicity but does not affect intracellular proliferation in U937 cells. This indicates that the pore formation promoted by L. pneumophila may not be involved in translocation of effector molecules into host cells (23,24).…”

Application of unstable Gfp variants to the kinetic study of Legionella pneumophila icm gene expression during infection

“…It is known that the IcmT protein is essential for pore formation and intracellular trafficking of L. pneumophila within Acanthomoeba polyphaga (Molmeret et al, 2002). The IcmQ protein is also involved in the pore-forming process (Feldman et al, 2005).…”