Growth-related changes in intracellular spermidine and its effect on efflux pump expression and quorum sensing in Burkholderia pseudomallei

Abstract

TheBurkholderia pseudomalleiBpeAB-OprB resistance-nodulation-division (RND) family pump effluxes aminoglycoside and macrolide antibiotics as well as acylhomoserine lactones (AHLs) involved in quorum sensing. Expression ofbpeA–lacZwas cell density-dependent and was inducible in the presence of these compounds. Intracellular levels of spermidine andN-acetylspermidine increased with cell density in wild-typeB. pseudomalleiKHW, but were always lower in thebpeABpump mutant at all growth phases. The significance of changes in intracellular spermidine on efflux pump expression was demonstrated by the disruption of the binding of the BpeR repressor protein to thebpeABoprBregulatory regionin vitroin the presence of increasing spermidine concentrations. This was supported by dose-dependent activation ofbpeA–lacZtranscriptionin vivoin the presence of exogenous spermidine andN-acetylspermidine, thus implicating the involvement of the BpeAB-OprB pump in spermidine homeostasis inB. pseudomallei. Consequently, inhibition of intracellular spermidine synthesis reduced the efflux of AHLs by BpeAB-OprB. Other potential therapeutic applications of spermidine synthase inhibitors include the reduction of swimming motility and biofilm formation byB. pseudomallei.