title: Rapid escape of the dot/icm mutants of Legionella pneumophila into the cytosol of mammalian and protozoan cells.
abstract: The Legionella pneumophila-containing phagosome evades endocytic fusion and intercepts endoplasmic reticulum (ER)-to-Golgi vesicle traffic, which is believed to be mediated by the Dot/Icm type IV secretion system. Although phagosomes harboring dot/icm mutants are thought to mature through the endosomal-lysosomal pathway, colocalization studies with lysosomal markers have reported contradictory results. In addition, phagosomes harboring the dot/icm mutants do not interact with endocytosed materials, which is inconsistent with maturation of the phagosomes in the endosomal-lysosomal pathway. Using multiple strategies, we show that the dot/icm mutants defective in the Dot/Icm structural apparatus are unable to maintain the integrity of their phagosomes and escape into the cytoplasm within minutes of entry into various mammalian and protozoan cells in a process independent of the type II secretion system. In contrast, mutants defective in cytoplasmic chaperones of Dot/Icm effectors and rpoS, letA/S, and letE regulatory mutants are all localized within intact phagosomes. Importantly, non-dot/icm L. pneumophila mutants whose phagosomes acquire late endosomal-lysosomal markers are all located within intact phagosomes. Using high-resolution electron microscopy, we show that phagosomes harboring the dot/icm transporter mutants do not fuse to lysosomes but are free in the cytoplasm. Inhibition of ER-to-Golgi vesicle traffic by brefeldin A does not affect the integrity of the phagosomes harboring the parental strain of L. pneumophila. We conclude that the Dot/Icm transporter is involved in maintaining the integrity of the L. pneumophila phagosome, independent of interception of ER-to-Golgi vesicle traffic, which is a novel function of type IV secretion systems.
authors: Department of Microbiology and Immunology, University of Louisville College of Medicine, Louisville, KY 40292, USA.
authors: Maëlle
authors: M
authors: Molmeret
authors: Marina
authors: M
authors: Santic'
authors: Rexford
authors: R
authors: Asare
authors: Reynold A
authors: RA
authors: Carabeo
authors: Yousef
authors: Y
authors: Abu Kwaik
mesh_terms: D000048:Acanthamoeba / Q000254:growth & development / Q000382:microbiology* / Q000648:ultrastructure; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003600:Cytosol / Q000382:microbiology*; D004847:Epithelial Cells / Q000382:microbiology / Q000648:ultrastructure; D006801:Humans; D016952:Legionella pneumophila / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity* / Q000502:physiology; D008264:Macrophages / Q000382:microbiology* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D009154:Mutation; D010588:Phagosomes / Q000382:microbiology / Q000648:ultrastructure*; D013997:Time Factors; D020298:U937 Cells
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C440002:DotA protein, Legionella pneumophila; D008565:Membrane Proteins; C443480:icmT protein, Legionella pneumophila