Open Access Highly Accessed Research article

Extensive recombination events and horizontal gene transfer shaped the Legionella pneumophila genomes

Laura Gomez-Valero12, Christophe Rusniok12, Sophie Jarraud345, Benoit Vacherie6, Zoé Rouy67, Valerie Barbe6, Claudine Medigue67, Jerome Etienne345 and Carmen Buchrieser12*

Author Affiliations

1 Institut Pasteur, Biologie des Bactéries Intracellulaires, 75724, Paris, France

2 CNRS URA 2171, 75724, Paris, France

3 Université de Lyon, Lyon, France, Centre National de Référence des Legionella, Lyon, France

4 INSERM, U851, 69007 Lyon, France

5 Hospices Civils de Lyon, Lyon, France

6 CEA/DSV/FAR/IG/Genoscope Laboratoire de Génomique Comparative, Evry Cedex, France

7 CNRS UMR8030 Laboratoire d'Analyses Bioinformatiques en Métabolisme et Génomique, Evry, France

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BMC Genomics 2011, 12:536  doi:10.1186/1471-2164-12-536

Published: 1 November 2011

Abstract

Background

Legionella pneumophila is an intracellular pathogen of environmental protozoa. When humans inhale contaminated aerosols this bacterium may cause a severe pneumonia called Legionnaires' disease. Despite the abundance of dozens of Legionella species in aquatic reservoirs, the vast majority of human disease is caused by a single serogroup (Sg) of a single species, namely L. pneumophila Sg1. To get further insights into genome dynamics and evolution of Sg1 strains, we sequenced strains Lorraine and HL 0604 1035 (Sg1) and compared them to the available sequences of Sg1 strains Paris, Lens, Corby and Philadelphia, resulting in a comprehensive multigenome analysis.

Results

We show that L. pneumophila Sg1 has a highly conserved and syntenic core genome that comprises the many eukaryotic like proteins and a conserved repertoire of over 200 Dot/Icm type IV secreted substrates. However, recombination events and horizontal gene transfer are frequent. In particular the analyses of the distribution of nucleotide polymorphisms suggests that large chromosomal fragments of over 200 kbs are exchanged between L. pneumophila strains and contribute to the genome dynamics in the natural population. The many secretion systems present might be implicated in exchange of these fragments by conjugal transfer. Plasmids also play a role in genome diversification and are exchanged among strains and circulate between different Legionella species.

Conclusion

Horizontal gene transfer among bacteria and from eukaryotes to L. pneumophila as well as recombination between strains allows different clones to evolve into predominant disease clones and others to replace them subsequently within relatively short periods of time.