The Rhl quorum sensing system is at the top of the regulatory hierarchy under phosphate limiting conditions in Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is a major nosocomial pathogen that presents high-level resistance to antibiotics. Its ability to cause infections relies on the production of multiple virulence factors. Quorum sensing (QS) regulates the expression of many of these virulence factors through three QS systems: Las, Rhl and PQS. The Las system positively regulates the other two systems, so it is the top of a hierarchized regulation. Nevertheless, clinical and environmental strains that lack a functional Las system have been isolated and surprisingly, some of them still have the ability to produce virulence factors and infect animal models, so it has been suggested that the hierarchy could be flexible under some conditions or atypical strains. Here we analyze the PAO1 type strain and its Delta lasR-derived mutant and report for the first time a growth condition (phosphate limitation) where LasR absence has no effect either on virulence factors production nor on the gene expression profile, in contrast to a condition of phosphate repletion where the LasR hierarchy is maintained This work provides evidence on how the QS hierarchy can change from being strictly LasR-dependent to a LasR-independent Rh1R-based hierarchy under phosphate limitation even in the PAO1 type strain.

Automated summary

This study reveals that under phosphate limitation, even in the PAO1 type strain, the absence of LasR has no effect on the production of virulence factors and gene expression profile, whereas in a condition of phosphate repletion, the LasR hierarchy is maintained.