The small RNA ReaL: a novel regulatory element embedded in the Pseudomonas aeruginosa quorum sensing networks.

The small RNA ReaL of the opportunistic pathogen Pseudomonas aeruginosa has been characterized. Our results indicate that ReaL contributes to P. aeruginosa virulence. In the Galleria mellonella infection model, reaL gene deletion resulted in decreased virulence, while ReaL overexpression resulted in a hyper-virulent phenotype. We also demonstrate that ReaL is embedded in the P. aeruginosa quorum sensing (QS) with the role of linking las to pqs systems. We show that ReaL is negatively regulated by the las regulator LasR and impacts positively the synthesis of the pqs quinolone signal PQS by a positive post-transcriptional effect on the pqsC gene. Perturbations of ReaL levels affect pyocyanin synthesis, biofilm formation and swarming motility, processes that are known to be influenced by PQS synthesis. In addition to being regulated by LasR, ReaL is also responding to infection relevant cues that P. aeruginosa can experience in mammalian hosts such as temperature and oxygen availability. Furthermore, ReaL shows a growth phase-dependent pattern of expression, being up-regulated in stationary phase, due to the activity of the alternative σ factor RpoS. Together, these regulations of ReaL expression are expected to contribute to the fine co-modulation of PQS synthesis and, ultimately, virulence.