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Tractable Mammalian Cell Infections with Protozoan-primed Bacteria
Published on: April 2, 2013
Legionella pneumophila prevents proliferation of its natural host Acanthamoeba castellanii
Luce Mengue1, Matthieu Régnacq2, Willy Aucher1
1Laboratoire Ecologie et Biologie des Interactions, Microbiologie de l'Eau, Université de Poitiers, UMR CNRS 7267, Poitiers, France.
Abstract:
Legionella pneumophila is a ubiquitous, pathogenic, Gram-negative bacterium responsible for legionellosis. Like many other amoeba-resistant microorganisms, L. pneumophila resists host clearance and multiplies inside the cell. Through its Dot/Icm type IV secretion system, the bacterium injects more than three hundred effectors that modulate host cell physiology in order to promote its own intracellular replication. Here we report that L. pneumophila prevents proliferation of its natural host Acanthamoeba castellanii. Infected amoebae could not undergo DNA replication and no cell division was observed. The Dot/Icm secretion system was necessary for L. pneumophila to prevent the eukaryotic proliferation. The absence of proliferation was associated with altered amoebal morphology and with a decrease of mRNA transcript levels of CDC2b, a putative regulator of the A. castellanii cell cycle. Complementation of CDC28-deficient Saccharomyces cerevisiae by the CDC2b cDNA was sufficient to restore proliferation of CDC28-deficient S. cerevisiae and suggests for the first time that CDC2b from A. castellanii could be functional and a bona fide cyclin-dependent kinase. Hence, our results reveal that L. pneumophila impairs proliferation of A. castellanii and this effect could involve the cell cycle protein CDC2b.
Insights
Legionella pneumophila infection stops Acanthamoeba castellanii cell division and DNA replication. This bacterial effect, mediated by the Dot/Icm system, involves the host cell cycle regulator CDC2b.
Area of Science:
- Microbiology
- Cell Biology
- Molecular Biology
Background:
- Legionella pneumophila is a Gram-negative bacterium causing legionellosis.
- It resists host defenses and replicates intracellularly using the Dot/Icm type IV secretion system.
- L. pneumophila injects numerous effectors to manipulate host cell functions.
Purpose of the Study:
- To investigate the effect of L. pneumophila infection on the proliferation of its natural host, Acanthamoeba castellanii.
- To determine the role of the Dot/Icm secretion system in this interaction.
- To identify host cell factors involved in the inhibition of proliferation.
Main Methods:
- Infection of Acanthamoeba castellanii with L. pneumophila.
- Analysis of amoebal DNA replication and cell division.
- Assessment of the necessity of the Dot/Icm secretion system.
- Measurement of mRNA transcript levels of CDC2b.
- Functional complementation assay in Saccharomyces cerevisiae.
Main Results:
- L. pneumophila prevented DNA replication and cell division in A. castellanii.
- The Dot/Icm secretion system was essential for inhibiting eukaryotic proliferation.
- Infected amoebae showed altered morphology and decreased CDC2b mRNA levels.
- CDC2b from A. castellanii restored proliferation in CDC28-deficient yeast, indicating it's a functional cyclin-dependent kinase.
Conclusions:
- L. pneumophila actively impairs the proliferation of A. castellanii.
- This inhibition mechanism likely involves the manipulation of the host cell cycle, potentially through the CDC2b protein.
- The findings reveal a novel aspect of L. pneumophila's host-pathogen interactions.
