Legionella pneumophila adaptation to intracellular life and the host response: Clues from genomics and transcriptomics

Legionella pneumophila is the causative agent of the pneumonia-like Legionnaires' disease. The bacterium's survival and spread depend on the ability to replicate inside eukaryotic phagocytic cells. A particular feature of Legionella is its dual host system allowing the intracellular growth in protozoa like Acanthamoeba castellanii, and during infection in human alveolar macrophages. Genome analysis and comparisons as well as expression profiling of the pathogen and the host helped to identify regulatory circuits mediating adaptation of the L. pneumophila transcriptome to the intracellular environment and gave clues for the metabolic needs of intracellular Legionella. This review will summarize what is currently known about intracellular gene expression of L. pneumophila, the transcriptional host response of the model host Dictyostelium discoideum and will present hypotheses drawn from these data with respect to subversion of host cell functions and virulence of L. pneumophila.