Legionella pneumophila prevents proliferation of its natural host Acanthamoeba castellanii.

Luce Mengue,Yann Héchard,Willy Aucher,Matthieu Régnacq,Ascel Samba-Louaka,Emilie Portier

doi:10.1038/srep36448

Luce Mengue, Yann Héchard + Show 4 more

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https://doi.org/10.1038/srep36448

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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.

Highlights

Legionella pneumophila is a pathogenic Gram-negative bacterium found in natural and artificial aqueous environments[1]
The eukaryotic cell cycle is driven by a class of serine/ threonine kinases named Cyclin-Dependent Kinases (CDKs) that act in concert with protein regulatory subunits called Cyclins[9]
The genetic complementation of CDC2b cDNA from Acanthamoeba in CDC28-deficient S. cerevisiae demonstrates that CDC2b is a functional CDK and suggests that the cell cycle inhibition of Acanthamoeba upon infection could be related to down-regulation of CDC2b mRNA

Summary

Introduction

Legionella pneumophila is a pathogenic Gram-negative bacterium found in natural and artificial aqueous environments[1]. L. pneumophila has evolved a number of mechanisms to modulate amoebal signal-transduction pathways to its advantage to support its replication This successful strategy lies in the ability of L. pneumophila to perturb essential functions such as transcription, translation, cytoskeleton machineries, organelle function, vesicular trafficking, autophagy and host survival processes[5]. During infection of amoebae or alveolar macrophages, L. pneumophila injects more than three hundred effectors through a type IV secretion system (T4SS) called Dot/Icm (Defect in organelle trafficking; Intracellular multiplication) which is critical for resistance to host digestion, replication and exit of the bacterium from the cell[6,7]. We show that L. pneumophila is able to prevent the proliferation of its natural host Acanthamoeba This effect depends on the number of bacteria per amoebae and required the Dot/Icm secretion system. The genetic complementation of CDC2b cDNA from Acanthamoeba in CDC28-deficient S. cerevisiae demonstrates that CDC2b is a functional CDK and suggests that the cell cycle inhibition of Acanthamoeba upon infection could be related to down-regulation of CDC2b mRNA

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