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The autoinducer synthase LqsA and putative sensor kinase LqsS regulate phagocyte interactions, extracellular filaments and a genomic island of Legionella pneumophila

Authors

  • André Tiaden,

    1. Institute of Molecular Life Sciences, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
    2. Institute of Microbiology, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
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    • These authors contributed equally to this work.

  • Thomas Spirig,

    1. Institute of Microbiology, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
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    • Present address: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1570, USA.

    • These authors contributed equally to this work.

  • Tobias Sahr,

    1. Institut Pasteur, Unité de Biologie des Bactéries Intracellulaires and CNRS URA 2171, 28 Rue du Dr Roux, 75724 Paris, France.
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  • Martin A. Wälti,

    1. Institute of Molecular Life Sciences, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
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  • Karin Boucke,

    1. Institute of Molecular Life Sciences, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
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  • Carmen Buchrieser,

    1. Institut Pasteur, Unité de Biologie des Bactéries Intracellulaires and CNRS URA 2171, 28 Rue du Dr Roux, 75724 Paris, France.
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  • Hubert Hilbi

    Corresponding author
    1. Institute of Molecular Life Sciences, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
    2. Institute of Microbiology, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland.
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E-mail hubert.hilbi@imls.uzh.ch; Tel. (+41) 44 635 4848; Fax (+41) 44 635 6822.

Summary

The amoebae-resistant opportunistic pathogen Legionella pneumophila employs a biphasic life cycle to replicate in host cells and spread to new niches. Upon entering the stationary growth phase, the bacteria switch to a transmissive (virulent) state, which involves a complex regulatory network including the lqs gene cluster (lqsA-lqsR-hdeD-lqsS). LqsR is a putative response regulator that promotes host–pathogen interactions and represses replication. The autoinducer synthase LqsA catalyses the production of the diffusible signalling molecule 3-hydroxypentadecan-4-one (LAI-1) that is presumably recognized by the sensor kinase LqsS. Here, we analysed L. pneumophila strains lacking lqsA or lqsS. Compared with wild-type L. pneumophila, the ΔlqsS strain was more salt-resistant and impaired for the Icm/Dot type IV secretion system-dependent uptake by phagocytes. Legionella pneumophila strains lacking lqsS, lqsR or the alternative sigma factor rpoS sedimented more slowly and produced extracellular filaments. Deletion of lqsA moderately reduced the uptake of L. pneumophila by phagocytes, and the defect was complemented by expressing lqsA in trans. Unexpectedly, the overexpression of lqsA also restored the virulence defect and reduced filament production of L. pneumophila mutant strains lacking lqsS or lqsR, but not the phenotypes of strains lacking rpoS or icmT. These results suggest that LqsA products also signal through sensors not encoded by the lqs gene cluster. A transcriptome analysis of the ΔlqsA and ΔlqsS mutant strains revealed that under the conditions tested, lqsA regulated only few genes, whereas lqsS upregulated the expression of 93 genes at least twofold. These include 52 genes clustered in a 133 kb high plasticity genomic island, which is flanked by putative DNA-mobilizing genes and encodes multiple metal ion efflux pumps. Upon overexpression of lqsA, a cluster of 19 genes in the genomic island was also upregulated, suggesting that LqsA and LqsS participate in the same regulatory circuit.

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