MexT modulates virulence determinants in Pseudomonas aeruginosa independent of the MexEF-OprN efflux pump

In the human pathogen Pseudomonas aeruginosa, the LysR-family regulator MexT modulates the induction of the tripartite MexEF-OprN resistance nodulation-division multi-drug efflux system resulting in increased resistance to diverse antibiotics. The MexEF-OprN system is normally quiescent in wild-type cells, but is highly induced in nfxC-type phenotypic mutants in a MexT dependent manner.In addition to antibiotic resistance, induction of mexEF-oprN in nfxC-type mutants has been linked to reduced levels of homoserine lactone-dependent virulence traits, including pyocyanin, elastase, rhamnolipids and PQS and to reduced expression of type three secretion effector proteins. In this study, MexT is overexpressed in wild-type PAO1 and an isogenic mexEF deletion mutant to determine if MexT regulates diverse virulence phenotypes dependent or independent of MexEF-OprN. It is shown that MexT regulates type three secretion, pyocyanin production and early surface attachment independent of MexEF-OprN. In contrast, MexT modulation of the expression of the virulence genes rhlA, lasB and hcnB is dependent on MexEF-OprN, which apparently mediates these effects via efflux of cell-signaling intermediates. The data presented demonstrates that MexT may play a more global role in modulating P. aeruginosa virulence than previously reported and suggests that MexT regulates diverse targets that mediate phenotypic alterations independent of MexEF-OprN.