RND type efflux pump system MexAB-OprM of pseudomonas aeruginosa selects bacterial languages, 3-oxo-acyl-homoserine lactones, for cell-to-cell communication

<jats:title>Abstract</jats:title> <jats:sec> <jats:title>Background</jats:title> <jats:p>Bacteria release a wide variety of small molecules including cell<jats:bold>-</jats:bold> to<jats:bold>-</jats:bold> cell signaling compounds. Gram-negative bacteria use a variety of self-produced autoinducers such as acylated homoserine lactones (acyl<jats:bold>-</jats:bold> HSLs) as signal compounds for quorum sensing (QS) within and between bacterial species. QS plays a significant role in the pathogenesis of infectious diseases and in beneficial symbiosis by responding to acyl<jats:bold>-</jats:bold> HSLs in <jats:italic>Pseudomonas aeruginosa</jats:italic>. It is considered that the selection of bacterial languages is necessary to regulate gene expression and thus it leads to the regulation of virulence and provides a growth advantage in several environments. In this study, we hypothesized that RND-type efflux pump system MexAB<jats:bold>-</jats:bold> OprM of <jats:italic>P. aeruginosa</jats:italic> might function in the selection of acyl<jats:bold>-</jats:bold> HSLs, and we provide evidence to support this hypothesis.</jats:p> </jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Loss of MexAB<jats:bold>-</jats:bold> OprM due to deletion of <jats:italic>mexB</jats:italic> caused increases in QS responses, as shown by the expression of <jats:italic>gfp</jats:italic> located downstream of the <jats:italic>lasB</jats:italic> promoter and LasB elastase activity, which is regulated by a LasR<jats:bold>-</jats:bold> 3<jats:bold>-</jats:bold> oxo<jats:bold>-</jats:bold> C12<jats:bold>-</jats:bold> HSL complex. Either complementation with a plasmid containing wild<jats:bold>-</jats:bold> type <jats:italic>mexB</jats:italic> or the addition of a LasR<jats:bold>-</jats:bold> specific inhibitor, patulin, repressed these high responses to 3<jats:bold>-</jats:bold> oxo<jats:bold>-</jats:bold> acyl<jats:bold>-</jats:bold> HSLs. Furthermore, it was shown that the acyl<jats:bold>-</jats:bold> HSLs<jats:bold>-</jats:bold> dependent response of <jats:italic>P. aeruginosa</jats:italic> was affected by the inhibition of MexB transport activity and the <jats:italic>mexB</jats:italic> mutant. The <jats:italic>P. aeruginosa</jats:italic> MexAB<jats:bold>-</jats:bold> OprM deletion mutant showed a strong QS response to 3<jats:bold>-</jats:bold> oxo<jats:bold>-</jats:bold> C10<jats:bold>-</jats:bold> HSL produced by <jats:italic>Vibrio anguillarum</jats:italic> in a bacterial cross<jats:bold>-</jats:bold> talk experiment.</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusion</jats:title> <jats:p>This work demonstrated that MexAB<jats:bold>-</jats:bold> OprM does not control the binding of LasR to 3-oxo-Cn-HSLs but rather accessibility of non-cognate acyl-HSLs to LasR in <jats:italic>P. aeruginosa</jats:italic>. MexAB<jats:bold>-</jats:bold> OprM not only influences multidrug resistance, but also selects acyl<jats:bold>-</jats:bold> HSLs and regulates QS in <jats:italic>P. aeruginosa</jats:italic>. The results demonstrate a new QS regulation mechanism via the efflux system MexAB<jats:bold>-</jats:bold> OprM in <jats:italic>P. aeruginosa</jats:italic>.</jats:p> </jats:sec>