Transcriptome of Legionella pneumophila rpoS mutant in water

Legionella pneumophila is a water-borne pathogen, and thus survival in the aquatic environment is central to its transmission to humans. Hence, identifying genes required for its survival in water could help prevent Legionnaires’ disease outbreaks. In the present study, we investigate for the first time the role of the sigma factor RpoS in promoting the survival in water, where L. pneumophila experiences total nutrient deprivation. The rpoS mutant showed a significant survival defect compared to the wild-type strain in defined water medium (DFM). Then, we analyzed the transcriptome of the rpoS mutant during exposure to water using whole genome microarray analysis. We found that RpoS negatively affects the expression of several genes, including genes required for replication, cell division, translation and transcription, suggesting that the mutant fails to shutdown major metabolic programs. The WT and rpoS mutant were grown to exponential phase in rich AYE broth, washed three times in DFM (NaCl 0.5 g/L, KH2PO40.2 g/L, KCl 0.5 g/L, pH=6.9) and resuspended in DFM at an OD600 of 0.1, After 24h exposure, RNA was extracted.