title: Extensive recombination events and horizontal gene transfer shaped the Legionella pneumophila genomes.
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.
  
  
  CONCLUSIONS
  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.
authors: Institut Pasteur, Biologie des Bactéries Intracellulaires, 75724, Paris, France.
authors: Laura
authors: L
authors: Gomez-Valero
authors: Christophe
authors: C
authors: Rusniok
authors: Sophie
authors: S
authors: Jarraud
authors: Benoit
authors: B
authors: Vacherie
authors: Zoé
authors: Z
authors: Rouy
authors: Valerie
authors: V
authors: Barbe
authors: Claudine
authors: C
authors: Medigue
authors: Jerome
authors: J
authors: Etienne
authors: Carmen
authors: C
authors: Buchrieser
mesh_terms: D005075:Biological Evolution; D022761:Gene Transfer, Horizontal; D016680:Genome, Bacterial; D016952:Legionella pneumophila / Q000145:classification / Q000235:genetics*; D010802:Phylogeny; D011110:Polymorphism, Genetic; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA