Analysis of Gene Expression in Legionella during Axenic Growth and Infection

Abstract

To understand the genetic basis of the ability of Legionella to adapt to a wide variety of different environmental settings, the authors have initiated a long-term genome-wide gene expression profiling study of Legionella pneumophila wild-type strains Philadelphia 1 and JR32 and several Legionella mutants during their growth in rich axenic media as well as at different stages of Acanthamoeba infection using whole-genome microarrays. The gene expression measurements for key operons were independently confirmed by real-time PCR. Gene expression profiles of wild type and rpoS mutants were compared during growth in rich axenic media. About 30% of the bacterial genome was found to be expressed under any single condition tested in the axenic growth experiments. Infection was initiated by centrifugation of the bacteria onto the adherent amoebae. About 500 genes were found to be expressed during the internalization and early stages of infection; 78 of them were also expressed during growth in liquid culture. This chapter provides a comparison of expressed gene complements between axenic growth and infection and some gene ontology (GO) functional gene categories expressed during the Acanthamoeba infection. Further studies should provide a more detailed picture of coordinated gene expression during Legionella infection as well as the molecular events that accompany it.