Legionella pneumophila - Host Interactions: Insights Gained from Comparative Genomics and Cell Biology

Legionella pneumophila is the etiological agent of Legionnaires' disease and of the less acute disease Pontiac fever. It is a Gram-negative bacterium present in fresh and artificial water environments that replicates in protozoan hosts and is also found in biofilms. Replication within protozoa is essential for the survival of the bacterium. The last years have seen a giant step forward in the genomics of L. pneumophila. The establishment and publication of the complete genome sequences of three clinical L. pneumophila isolates in 2004 and a fourth in 2007 has paved the way for major breakthroughs in understanding the biology of L. pneumophila in particular and Legionella in general. Sequence analysis identified several specific features of Legionella: (i) an extraordinary genetic diversity among the different isolates and (ii) the presence of an unexpected high number and variety of eukaryotic-like proteins, predicted to be involved in the exploitation of the host cellular processes by mimicking specific eukaryotic functions. In this chapter, we will first discuss the insights gained from genomics by highlighting the characteristic features and common traits of the four L. pneumophila genomes obtained through genome analysis and comparison and then we will focus on the newest results obtained by functional analysis of different eukaryotic-like proteins and describe their involvementin the pathogenicity of L. pneumophila.