Inactivation of MexT in Pseudomonas aeruginosa destabilizes cooperation and favors the emergence of a unique quorum sensing variant

Quorum sensing governs cooperative activities and has been used as a model for studying cooperative behaviors in bacterial populations. Pseudomonas aeruginosa has two interlinked acyl-homoserine lactone quorum sensing circuits, LasR-I and RhlR-I; the relationship between these circuits is influenced by a regulator called MexT. Inactivation of MexT results in enhanced activity of the quorum sensing transcription factor, RhlR, and we found that it also destabilized cooperative behaviors in this bacterium. MexT-inactive strains also reproducibly support the emergence of a specific LasR variant, V226I, of P. aeruginosa, offering insight into evolutionary pressures that select for mutations in quorum sensing transcription factors and, by extension, a method for bacteria to alter the cohort of genes that are quorum-controlled.