D’Auria et al. BMC Genomics 2010, 11:181 http://www.biomedcentral.com/1471-2164/11/181 R E S E A R C H A R T I C L E Open Access Legionella pneumophila pangenome reveals strain-specific virulence factors Giuseppe D’Auria1,2*, Nuria Jiménez-Hernández1,2, Francesc Peris-Bondia3, Andrés Moya1,2,3, Amparo Latorre1,2,3 Abstract Background: Legionella pneumophila subsp. pneumophila is a gram-negative g-Proteobacterium and the causative agent of Legionnaires’ disease, a form of epidemic pneumonia. It has a water-related life cycle. In industrialized cities L. pneumophila is commonly encountered in refrigeration towers and water pipes. Infection is always via infected aerosols to humans. Although many efforts have been made to eradicate Legionella from buildings, it still contaminates the water systems. The town of Alcoy (Valencian Region, Spain) has had recurrent outbreaks since 1999. The strain “Alcoy 2300/99” is a particularly persistent and recurrent strain that was isolated during one of the most significant outbreaks between the years 1999-2000. Results: We have sequenced the genome of the particularly persistent L. pneumophila strain Alcoy 2300/99 and have compared it with four previously sequenced strains known as Philadelphia (USA), Lens (France), Paris (France) and Corby (England). Pangenome analysis facilitated the identification of strain-specific features, as well as some that are shared by two or more strains. We identified: (1) three islands related to anti-drug resistance systems; (2) a system for transport and secretion of heavy metals; (3) three systems related to DNA transfer; (4) two CRISPR (Clustered Regularly Inter- spaced Short Palindromic Repeats) systems, known to provide resistance against phage infections, one similar in the Lens and Alcoy strains, and another specific to the Paris strain; and (5) seven islands of phage-related proteins, five of which seem to be strain-specific and two shared. Conclusions: The dispensable genome disclosed by the pangenomic analysis seems to be a reservoir of new traits that have mainly been acquired by horizontal gene transfer and could confer evolutionary advantages over strains lacking them. Background Legionella pneumophila is a gram-negative facultative intracellular pathogen, identified as the infectious agent of the Legionnaire’s disease (LD) or Legionellosis in 1977 [1]. It is found in aquatic environments parasitiz- ing its natural hosts, amoebae and protozoa. From this environment, Legionella can colonize water treatment plants, such as refrigeration towers, potable water pipes, etc., and can cause infections in humans, when infected aerosols are inhaled [2,3]. Despite efforts to keep water systems free of Legionella, this pathogen is still causing infection throughout the world, including Spain, where it is endemic in some areas. From 1989 to 2005, around 310 outbreaks with 2,974 cases were recorded world- wide. In 2002 and 2005 there were two important * Correspondence: dauria_giu@gva.es 1CIBER en Epidemiología y Salud Pública (CIBERESP), Barcelona, Spain epidemic events with 1,461 and 1,292 cases respectively. In Alcoy, an industrial town in the Valencian Region (Spain), a large outbreak occurred during 1999-2000. A strain that had caused several outbreaks and many cases, named “Alcoy 2300/99”, was isolated from a patient in that outbreak [4]. Since then, recurrent epi- demics in Alcoy have harbored Alcoy 2300/99. Currently, the genomes of five L. pneumophila strains are available: Philadelphia (Lpg, USA) [5], Lens (Lpl, France) and Paris (Lpp, France) [6], Corby (Lpc, England) [7] and Alcoy (Lpa, Spain) (reported in this work). As with the majority of other pathogenic Legio- nella strains, immunoassay analysis defined them as belonging to the serogroup 1 [8]. A phylogeny based on Multi Locus Sequence Typing (MLST) showed that all strains are closely related, Alcoy and Corby being the closest [9]. © 2010 D’Auria et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.