Bringing the Genome of Legionella pneumophila to Life: the Transcriptional Program during Infection of Acanthamoeba castellanii

Abstract

A whole-genome microarray was constructed which contained 3,823 gene-specific oligonucleotides representing every gene predicted in the Legionella pneumophila strain Paris genome plus each loci specific to strains Lens (302 genes) and Philadelphia. In this short article, some results of the in vivo transcriptional program of the three L. pneumophila strains during their life cycles in the natural eukaryotic host Acanthamoeba castellanii will be presented. A biphasic life cycle is clearly evident from the transcriptional data, with sets of replicative phase (RP) genes upregulated at the earlier time point and transmissive phase (TP) genes upregulated at the later time points. The global transcriptional programs of all three L. pneumophila strains were very similar, indicating that common regulatory mechanisms govern their life cycles. When switching from a fast-growing bacterium to a motile, highly infectious microbe, the pathogen fundamentally alters its transcriptional program. Among the most significantly upregulated genes in the TP, the authors identified four two-component systems, six LysR-family members, four additional transcriptional regulators [CpxR, PaiA-, MoxR and TetR-like], and two integration host factors. The findings provide a valuable resource and conceptual framework to increase knowledge of the Legionella life cycle and the host functions exploited during infection of amoebae and macrophages.