title: Transcriptomic changes of Legionella pneumophila in water.
abstract: BACKGROUND
  Legionella pneumophila (Lp) is a water-borne opportunistic pathogen. In water, Lp can survive for an extended period of time until it encounters a permissive host. Therefore, identifying genes that are required for survival in water may help develop strategies to prevent Legionella outbreaks.
  
  
  RESULTS
  We compared the global transcriptomic response of Lp grown in a rich medium to that of Lp exposed to an artificial freshwater medium (Fraquil) for 2, 6 and 24 hours. We uncovered successive changes in gene expression required for the successful adaptation to a nutrient-limited water environment. The repression of major pathways involved in cell division, transcription and translation, suggests that Lp enters a quiescent state in water. The induction of flagella associated genes (flg, fli and mot), enhanced-entry genes (enh) and some Icm/Dot effector genes suggests that Lp is primed to invade a suitable host in response to water exposure. Moreover, many genes involved in resistance to antibiotic and oxidative stress were induced, suggesting that Lp may be more tolerant to these stresses in water. Indeed, Lp exposed to water is more resistant to erythromycin, gentamycin and kanamycin than Lp cultured in rich medium. In addition, the bdhA gene, involved in the degradation pathway of the intracellular energy storage compound polyhydroxybutyrate, is also highly expressed in water. Further characterization show that expression of bdhA during short-term water exposure is dependent upon RpoS, which is required for the survival of Lp in water. Deletion of bdhA reduces the survival of Lp in water at 37 °C.
  
  
  CONCLUSIONS
  The increase of antibiotic resistance and the importance of bdhA to the survival of Lp in water seem consistent with the observed induction of these genes when Lp is exposed to water. Other genes that are highly induced upon exposure to water could also be necessary for Lp to maintain viability in the water environment.
authors: Department of Natural Resource Sciences, Faculty of Agricultural and Environmental Sciences, McGill University, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, Montreal, QC, H9X 3V9, Canada. laam.li@mail.mcgill.ca.
authors: Laam
authors: L
authors: Li
authors: Department of Natural Resource Sciences, Faculty of Agricultural and Environmental Sciences, McGill University, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, Montreal, QC, H9X 3V9, Canada. nissanka.mendis@mail.mcgill.ca.
authors: Nilmini
authors: N
authors: Mendis
authors: Department of Natural Resource Sciences, Faculty of Agricultural and Environmental Sciences, McGill University, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, Montreal, QC, H9X 3V9, Canada. hana.trigui@mcgill.ca.
authors: Hana
authors: H
authors: Trigui
authors: Department of Natural Resource Sciences, Faculty of Agricultural and Environmental Sciences, McGill University, 21,111 Lakeshore Road, Ste-Anne-de-Bellevue, Montreal, QC, H9X 3V9, Canada. sebastien.faucher2@mcgill.ca.
authors: Sébastien P
authors: SP
authors: Faucher
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D016000:Cluster Analysis; D024881:Drug Resistance, Bacterial; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D016952:Legionella pneumophila / Q000187:drug effects / Q000235:genetics*; D050296:Microbial Viability / Q000235:genetics; D009154:Mutation; D015203:Reproducibility of Results; D059467:Transcriptome; D014871:Water Microbiology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins