AmgRS‐mediated envelope stress‐inducible expression of the mexXY multidrug efflux operon of Pseudomonas aeruginosa

Amg RS is an envelope stress‐responsive two‐component system and aminoglycoside resistance determinant in Pseudomonas aeruginosa that is proposed to protect cells from membrane damage caused by aminoglycoside‐generated mistranslated polypeptides. Consistent with this, a Δ amgR strain showed increased aminoglycoside‐promoted membrane damage, damage that was largely absent in Amg RS ‐activated amgS‐ mutant strains. Intriguingly, one such mutation, V121G, while providing for enhanced resistance to aminoglycosides, rendered P. aeruginosa susceptible to several ribosome‐targeting nonaminoglycoside antimicrobials that are inducers and presumed substrates of the Mex XY ‐OprM multidrug efflux system. Surprisingly, the amg S V 121G mutation increased mex XY expression threefold, suggesting that export of these nonaminoglycosides was compromised in the amg S V 121G mutant. Nonetheless, a link was established between Amg RS activation and mex XY expression and this was confirmed in studies showing that aminoglycoside‐promoted mex XY expression is dependent on Amg RS . While nonaminoglycosides also induced mex XY expression, this was not Amg RS ‐dependent, consistent with these agents not generating mistranslated polypeptides and not activating Amg RS . The aminoglycoside inducibility of mex XY was abrogated in a mutant lacking the Amg RS target genes htpX and PA5528, encoding a presumed cytoplasmic membrane‐associated protease and a membrane protein of unknown function, respectively. Thus, aminoglycoside induction of mex XY is a response to membrane damage and activation of the Amg RS two‐component system.