Transcriptomic changes of Legionella pneumophila in water

Abstract

BackgroundLegionella 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.ResultsWe 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1869-6) contains supplementary material, which is available to authorized users.

Role of the LuxR family transcriptional regulator Lpg2524 in the survival ofLegionella pneumophilain water

“…Similar results were found for bdhA and lasM, which are required for survival in water only when the temperature is above 25°C (Li and Faucher 2016;Li et al 2015). Since ∆lpg2524 did not show a defect in water during short-term exposure at 55°C when compared to the WT (data not shown), it is unlikely that the defects we observed at 37°C and 42°C were due to a lower tolerance to high temperature.…”

“…CFU of each sample was monitored once per three weeks, once per two weeks and once per week, respectively. For the samples incubated at 42°C, Live/Dead staining and flow cytometry were used to determine the membrane integrity of Lp after 7 weeks as described previously (Li et al 2015). Freshly grown KS79 was used as the control for viable cells and KS79 boiled in a water bath for 10 minutes was used as the control for dead cells.…”

“…Since Lp induces expression of lpg2524 in water (Li et al 2015), we hypothesized that this gene could be important for survival in water and thus that the deletion of lpg2524 could D r a f t 12 result in a survival defect. Therefore, we exposed the WT strain, mutant strain ∆lpg2524 and complemented strain ∆lpg2524+plpg2524 to water at different temperatures and monitored their survival by CFU count.…”

“…Our previous transcriptomic studies have showed that RpoS positively regulates two genes significantly induced in water, bdhA and lpg1659 (lasM), that contribute to the long-term survival of Lp in water (Li and Faucher 2016;Li et al 2015).…”

Multiple major disease-associated clones ofLegionella pneumophilahave emerged recently and independently

“…S9). Among the 64 genes, some have been shown to play a role in intracellular infection such as the genes from the cytochrome c maturation (ccm) locus (Viswanathan et al 2002;Naylor and Cianciotto 2004), PilR (an important regulator for pilin and flagella synthesis), the phagosomal transporter family Pht (Sauer et al 2005), or the enhanced entry protein EnhA that was shown to be important for entry in phagocytic cells (Cirillo et al 2000) and during persistence in water environments (Li et al 2015).…”