The LetA/S two-component system regulates transcriptomic changes that are essential for the culturability of Legionella pneumophila in water

Abstract

Surviving the nutrient-poor aquatic environment for extended periods of time is important for the transmission of various water-borne pathogens, including Legionella pneumophila (Lp). Previous work concluded that the stringent response and the sigma factor RpoS are essential for the survival of Lp in water. In the present study, we investigated the role of the LetA/S two-component signal transduction system in the successful survival of Lp in water. In addition to cell size reduction in the post-exponential phase, LetS also contributes to cell size reduction when Lp is exposed to water. Importantly, absence of the sensor kinase results in a significantly lower survival as measured by CFUs in water at various temperatures and an increased sensitivity to heat shock. According to the transcriptomic analysis, LetA/S orchestrates a general transcriptomic downshift of major metabolic pathways upon exposure to water leading to better culturability, and likely survival, suggesting a potential link with the stringent response. However, the expression of the LetA/S regulated small regulatory RNAs, RsmY and RsmZ, is not changed in a relAspoT mutant, which indicates that the stringent response and the LetA/S response are two distinct regulatory systems contributing to the survival of Lp in water.

Transcriptomic Changes of Piscirickettsia salmonis During Intracellular Growth in a Salmon Macrophage-Like Cell Line

“…The N-terminus of P. salmonis LetS contains two conserved signal sensing domains: DUF2222 (residues 36-168) and HAMP (residues 191-243), and two transmembrane domains located between residues 10 to 32 and residues 165 to 187. C-terminal to these domains are found the transmitter, receiver, and histidine phosphotransfer domains, which is a characteristic structure of tripartite sensor kinases (Mendis et al, 2018). In L. pneumophila, LetS acts by shutting down a number of genes related to growth when the bacterium is exposed to water, improving its culturability and survival in a low-nutrient environment (Mendis et al, 2018).…”

A Clinical Overview of Hospital-Acquired Legionella Pneumonia: Prevention Is the Key?

“…In order to survive against harsh environmental conditions, legionella enters a "reversible dormant state", known as the viable but not culturable state (VBNCS) [24] When environmental conditions improve, like in the case of phagocytosis by Acanthamoeba castellanii, the bacterium represses its virulent traits and goes into its exponential phase, in which it replicates within the protozoa [6]. This process of replication takes round 15 hours to complete [25]. Once lack of nutrients and environmental stress strikes, L. pneumophila coordinates its differentiation to the mature intracellular form (MIF) and the stationary phase form (SPFs), both with virulent traits characterized by high motility and cytotoxicity and proceeds to lyse the cell and infect cells in proximity.…”

“…Once lack of nutrients and environmental stress strikes, L. pneumophila coordinates its differentiation to the mature intracellular form (MIF) and the stationary phase form (SPFs), both with virulent traits characterized by high motility and cytotoxicity and proceeds to lyse the cell and infect cells in proximity. Although studies are lacking on the mechanisms by which the host cell is lysed by the bacterium [24,25]. SPFs present flagella, loose outer membrane, and a well-defined inner membrane, while MIFs typically appear as stubby rods with complex envelope, both being able to colonize alveolar macrophages [24].…”

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

“…This response results in the production of chaperones and proteases to refold or destroy misfolded proteins and aggregates (14). In Lp, the two-component system LetA/S is the only regulatory system known to be important for surviving thermal stress (15).…”

“…A transcriptomic analysis of a letS mutant in water revealed that tsp is downregulated in the mutant (15). In addition, the expression of tsp was downregulated in a cpxR mutant grown to PE phase, suggesting CpxR is also required for expression of tsp in PE phase (41).…”