Legionella pneumophila (Lp) is the primary agent of Legionnaires'disease, a common and potentially fatal form of pneumonia. The bacterium is ubiquitous in natural and man-made water systems and infects the lungs after the inhalation of contaminated aerosols. In water and the lungs, Lp grows as an intracellular parasite, infecting either aquatic protozoa, macrophages, or epithelia. Previously, we determined that Lp possesses a type II secretion (T2S) system and hypothesized that proteins secreted by T2S are mediators of environmental persistence, intracellular infection, and virulence. During the last grant period, we documented that T2S is required for intracellular infection of amoebae, alveolar macrophages, and lung epithelia as well as bacterial persistence in the lungs of experimentally-infected mice. Proteomic analysis of Lp supernatants and in silico analysis of the Lp genome were then combined to reveal the extensive nature of the T2S output. In addition to predicted activities, which we confirmed, """"""""novel"""""""" exoproteins were identified that had no similarity to known proteins. Using mutants lacking one or more T2S-dependent exoproteins (effectors), we determined that a metalloprotease (ProA) and ribonuclease (SrnA) promote amoeba infection, phospholipases C (PlcA/B) and a chitinase (ChiA) facilitate infection of mammalian cells, and a novel protein (Lpg0264) promotes both amoebal and macrophage infection. In vivo competition assays then identified four T2S effectors that appear to promote Lp survival in lungs;i.e., ChiA, PlcA/B, Lpg0264, and an astacin-like protease (LegP). Additionally, we discovered that Lp exhibits a swarming phenotype on agar surfaces that is dependent upon T2S. In sum, Lp T2S is uniquely critical for intracellular infection, swarming, virulence, as well as low-temperature survival in water, elaborating more effectors and encoding a wider variety of activities than is appreciated for any other T2S system. In the current proposal, we will use genetics and various infection models and cell biological tools to i) determine the importance of a select number of new """"""""novel"""""""" effectors for intracellular infection, ii) determine the importance of T2S-dependent swarming for intracellular infection, iii) determine the intracellular location of and trafficking patterns influenced by ProA, SrnA, PlcA/B, and Lpg0264, and iv) confirm the importance of PlcA/B, Lpg0264, and LegP, the new novel effectors, and swarming in a murine model of pneumonia. The proposed studies will i) increase significantly our understanding of the pathogenesis of Lp, which is an important public health concern within the US and throughout the world, ii) expand our molecular understanding of the both bacterial protein secretion and intracellular infection, iii) have implications for other important, environmental pathogens that utilize or are predicted to use T2S, and iv) offer potential new targets for disease diagnosis, treatment, or prevention.

Public Health Relevance

We have discovered that the so-called type II secretion system of Legionella pneumophila promotes bacterial growth in mammalian host cells (e.g., macrophages and epithelial cells) and in the lungs of experimentally infected mice. We therefore hypothesize that the proteins (effectors) secreted by the bacterium through this system are virulence factors and therefore are potential targets for disease diagnosis or prevention. To test this hypothesis, we will i) characterize bacterial mutants that are lacking specific effectors using in vitro models of intracellular infection and an animal model of pneumonia in order to identify those effectors that promote infection, and ii) monitor the intracellular expression patterns of those proteins that are shown to be important for infection.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Special Emphasis Panel (ZRG1-IDM-H (02))
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Korpela, Jukka K
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Northwestern University at Chicago
Schools of Medicine
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White, Richard C; Gunderson, Felizza F; Tyson, Jessica Y et al. (2018) Type II Secretion-Dependent Aminopeptidase LapA and Acyltransferase PlaC Are Redundant for Nutrient Acquisition during Legionella pneumophila Intracellular Infection of Amoebas. MBio 9:
Mallama, Celeste A; McCoy-Simandle, Kessler; Cianciotto, Nicholas P (2017) The Type II Secretion System of Legionella pneumophila Dampens the MyD88 and Toll-Like Receptor 2 Signaling Pathway in Infected Human Macrophages. Infect Immun 85:
Cianciotto, Nicholas P; White, Richard C (2017) Expanding Role of Type II Secretion in Bacterial Pathogenesis and Beyond. Infect Immun 85:
Truchan, Hilary K; Christman, Harry D; White, Richard C et al. (2017) Type II Secretion Substrates of Legionella pneumophila Translocate Out of the Pathogen-Occupied Vacuole via a Semipermeable Membrane. MBio 8:
White, Richard C; Cianciotto, Nicholas P (2016) Type II Secretion Is Necessary for Optimal Association of the Legionella-Containing Vacuole with Macrophage Rab1B but Enhances Intracellular Replication Mainly by Rab1B-Independent Mechanisms. Infect Immun 84:3313-3327
DuMont, Ashley L; Karaba, Sara M; Cianciotto, Nicholas P (2015) Type II Secretion-Dependent Degradative and Cytotoxic Activities Mediated by Stenotrophomonas maltophilia Serine Proteases StmPr1 and StmPr2. Infect Immun 83:3825-37
Tyson, Jessica Y; Vargas, Paloma; Cianciotto, Nicholas P (2014) The novel Legionella pneumophila type II secretion substrate NttC contributes to infection of amoebae Hartmannella vermiformis and Willaertia magna. Microbiology 160:2732-44
Gunderson, Felizza F; Cianciotto, Nicholas P (2013) The CRISPR-associated gene cas2 of Legionella pneumophila is required for intracellular infection of amoebae. MBio 4:e00074-13
Cianciotto, Nicholas P (2013) Type II secretion and Legionella virulence. Curr Top Microbiol Immunol 376:81-102
Tyson, Jessica Y; Pearce, Meghan M; Vargas, Paloma et al. (2013) Multiple Legionella pneumophila Type II secretion substrates, including a novel protein, contribute to differential infection of the amoebae Acanthamoeba castellanii, Hartmannella vermiformis, and Naegleria lovaniensis. Infect Immun 81:1399-410

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