Legionella pneumophila replicates within a membrane-bounded compartment that is studded with ribosomes. In this study we investigated whether these ribosomes originate from the cytoplasmic pool or are associated host endoplasmic reticulum (ER). Immunofluorescence and electron microscopic localization studies of ER proteins in macrophages infected L. indicated bacteria reside surrounded by ER. An mutant grows slowly was slow to associate ER, providing genetic evidence support hypothesis...

To restrict infection by Legionella pneumophila, mouse macrophages require Naip5, a member of the nucleotide-binding oligomerization domain leucine-rich repeat family pattern recognition receptors, which detect cytoplasmic microbial products. We report that restricted L. pneumophila replication and initiated proinflammatory program cell death when flagellin contaminated their cytosol. Nuclear condensation, membrane permeability, interleukin-1β secretion were triggered type IV...

ABSTRACT In nature, Legionella pneumophila replicates exclusively as an intracellular parasite of amoebae, but it also persists in the environment a free-living microbe. Studies how this opportunistic pathogen recognizes and responds to distinct extracellular environments identified link between growth phase expression traits previously correlated with virulence. When cultured broth, only post-exponential-phase L. was sodium sensitive, cytotoxic, osmotically resistant, competent evade...

After ingestion by macrophages, Legionella pneumophila enter spacious vacuoles that are quickly enveloped endoplasmic reticulum (ER), then slowly transferred to lysosomes. Here we demonstrate the macrophage autophagy machinery recognizes pathogen phagosome as cargo for lysosome delivery. The conjugation enzyme Atg7 immediately translocated phagosomes harbouring virulent Legionella. Subsequently, Atg8, a second enzyme, and monodansyl-cadaverine (MDC), dye accumulates in acidic autophagosomes,...

Legionella pneumophila survives in aquatic environments, but replicates within amoebae or the alveolar macrophages of immunocompromised individuals. Here, signal transduction pathway that co-ordinates L. virulence expression response to amino acid depletion was investigated. To facilitate kinetic and genetic studies, a phenotypic reporter engineered by fusing flaA promoter sequences gene encoding green fluorescent protein. When subjected depletion, accumulated ppGpp converted from...

Pathogenic Legionella pneumophila evolved as a parasite of aquatic amoebae. To persist in the environment, microbe must be proficient at both replication and transmission. In laboratory cultures, nutrients become scarce stringent response-like pathway coordinates exit from exponential growth phase with induction traits correlated virulence, including motility. A screen for mutants that express flagellin gene poorly identified five activators virulence: LetA/LetS, two-component regulator...

After ingestion by macrophages, Legionella pneumophila inhibits acidification and maturation of its phagosome. a 6–10-h lag period, the bacteria replicate for 10–14 h until macrophage lysis releases dozens progeny. To examine whether growth phase intracellular L. determines fate phagosome, interactions between endosomal network pathogen vacuoles were analyzed throughout primary infection period. Surprisingly, as replicated exponentially, significant proportion acquired lysosomal...

Legionella pneumophila is an intracellular pathogen responsible for Legionnaires' disease. This bacterium uses the Dot/Icm type IV secretion system to inject a large number of bacterial proteins into host cells facilitate biogenesis phagosome permissive its growth. Like many highly adapted intravacuolar pathogens, L. able maintain neutral pH in lumen phagosome, particularly early phase infection. However, all cases, molecular mechanisms underlying this observation remain unknown. In report,...

Abstract The contribution of neutrophils to lethal sensitivity and cytokine balance governing T1 T2 host responses was assessed in a murine model Legionella pneumophila pneumonia. Neutrophil depletion by administration granulocyte-specific mAb RB6-8C5 at 1 day before infection rendered mice ∼100-fold more susceptible pneumonia induced L. pneumophila. However, this treatment did not alter early bacterial clearance, despite substantial decrease neutrophil influx time point. Cytokine profiles...

Summary Legionella pneumophila can replicate inside amoebae and also alveolar macrophages to cause Legionnaires’ Disease in susceptible hosts. When nutrients become limiting, a stringent‐like response coordinates the differentiation of L. transmissive form, process mediated by two‐component system LetA/S sigma factors RpoS FliA. Here we demonstrate that broadly conserved RNA binding protein CsrA is global repressor transmission phenotypes an essential activator intracellular replication. By...

Mutations in the SPT5 gene of Saccharomyces cerevisiae were isolated previously as suppressors delta insertion mutations at HIS4 and LYS2. In this study we have shown that spt5 suppress his4-912 lys2-128 alleles by altering transcription. We cloned found either an increase or a decrease copy number wild-type caused Spt- phenotype. Construction analysis null mutation demonstrated is essential for growth, suggesting may be required normal transcription large genes. The DNA sequence was...

Abstract The SPT4, SPT5 and SPT6 genes of Saccharomyces cerevisiae were identified originally by mutations that suppress delta insertion at HIS4 LYS2. Subsequent analysis has demonstrated spt4, spt5 spt6 confer similar pleiotropic phenotypes. They altering transcription are believed to be required for normal several other loci. We have now analyzed interactions between SPT6. First, the combination in any two these three causes lethality haploids. Second, some recessive different members this...

During phagocytosis, the phosphoinositide content of activated membrane decreases sharply, as does associated surface charge, which attracts polycationic proteins. The cytosolic leaflet plasma is enriched in phosphatidylserine (PS); however, a lack suitable probes has precluded investigation fate this phospholipid during phagocytosis. We used recently developed fluorescent biosensor to monitor distribution and dynamics PS phagosome formation maturation. Unlike polyphosphoinositides, persists...

When microbes contaminate the macrophage cytoplasm, leukocytes undergo a proinflammatory death that is initiated by nucleotide-binding-domain-, leucine-rich-repeat-containing proteins (NLR proteins) bind and activate caspase-1. We report these inflammasome components also regulate autophagy, vesicular pathway to eliminate cytosolic debris. In response infection with flagellate Legionella pneumophila, C57BL/6J mouse macrophages equipped caspase-1 NLR NAIP5 NLRC4 stimulated autophagosome...

Legionella pneumophila replicates within amoebae and macrophages causes the severe pneumonia Legionnaires' disease. When broth cultures enter post‐exponential growth (PE) phase or experience amino acid limitation, L. accumulates stringent response signal (p)ppGpp expresses traits likely to promote transmission a new phagocyte. The hypothesis that mechanism regulates virulence was bolstered by our finding avirulent mutant Lp120 contains an internal deletion in gene encoding stationary sigma...

Differentiation in response to environmental cues is integral the success of many intracellular pathogens. By characterizing a Legionella pneumophila mutant defective for differentiation broth and replication macrophages, we identified subfamily major facilitator superfamily transporters, here named Pht (phagosomal transporter), that also conserved two other vacuolar pathogens, Coxiella burnetii Francisella tularensis. Biolog phenotype microarray analysis indicated PhtA transports threonine,...

When cultured in broth to the transmissive phase, Legionella pneumophila infects macrophages by inhibiting phagosome maturation, whereas replicative-phase cells are transported lysosomes. Here we report that ability of L. inhibit phagosome-lysosome fusion correlated with developmentally regulated modifications pathogen's surface, as judged its lipopolysaccharide profile and binding a sialic acid-specific lectin hydrocarbon hexadecane. Likewise, composition membrane vesicles shed was...

During its life cycle, Legionella pneumophila alternates between a replicative and transmissive state. To determine their contributions to L. differentiation, the two ppGpp synthetases, RelA SpoT, were disrupted. Synthesis of was required for transmission, as relA spoT mutants killed during entry exit from macrophages. RelA, which senses amino acid starvation induced by serine hydroxamate, is dispensable in macrophages, spread efficiently. SpoT monitors fatty biosynthesis (FAB), since...

Background Recent studies have suggested that autophagy is utilized by cells as a protective mechanism against Listeria monocytogenes infection. Methodology/Principal Findings However we find has no measurable role in vacuolar escape and intracellular growth primary cultured bone marrow derived macrophages (BMDMs) deficient for (atg5−/−). Nevertheless, provide evidence the pore forming activity of cholesterol-dependent cytolysin listeriolysin O (LLO) can induce subsequent to infection L....

The regulation of innate immune responses during viral infection is a crucial step to promote antiviral reactions. Recent studies have drawn attention strong relationship pathogen-associated molecular pattern recognition with autophagy for activation APC function. Our initial observations indicated that autophagosomes formed in response respiratory syncytial virus (RSV) dendritic cells (DC). To further investigate whether RSV-induced DC and cytokine production were associated autophagy, we...