Legionella pneumophila's Tsp is important for surviving thermal stress in water and inside amoeba

Legionella pneumophila (Lp) is an inhabitant of natural and man-made water systems where it replicates within amoebae and ciliates and survives within biofilms. When Lp-contaminated aerosols are breathed in, Lp will enter the lungs and infect human alveolar macrophages, causing a severe pneumonia known as Legionnaires Disease. Lp is often found in hot water distribution systems (HWDS), which are linked to nosocomial outbreaks. Heat treatment is used to disinfect HWDS and reduce the concentration of Lp. However, Lp is often able to recolonize these water systems, indicating an efficient heat-shock response. Tail-specific proteases (Tsp) are typically periplasmic proteases implicated in degrading aberrant proteins in the periplasm and important for surviving thermal stress. In this paper, we show that Tsp, encoded by the lpg0499 gene in Lp Philadelphia-1, is important for surviving thermal stress in water and for optimal infection of amoeba when a shift in temperature occurs during intracellular growth. Tsp is expressed in the post-exponential phase but repressed in the exponential phase. The cis-encoded small regulatory RNA Lpr17 shows opposite expression, suggesting that it represses translation of tsp. In addition, tsp is regulated by CpxR, a major regulator in Lp, in a Lpr17-independent manner. Deletion of CpxR also reduced the ability of Lp to survive heat shock. In conclusion, this study shows that Tsp is an important factor for the survival and growth of Lp in water systems. IMPORTANCELegionella pneumophila (Lp) is a major cause of nosocomial and community-acquired pneumonia. Lp is found in water systems including hot water distribution systems. Heat treatment is a method of disinfection often used to limit Lps presence in such systems; however, the benefit is usually short term as Lp is able to quickly recolonize these systems. Presumably, Lp respond efficiently to thermal stress, but so far not much is known about the genes involved. In this paper, we show that the Tail-specific protease (Tsp) and the two-component system CpxRA are required for resistance to thermal stress, when Lp is free in water and when it is inside host cells. Our study identifies critical systems for the survival of Lp in its natural environment under thermal stress.