Role of the LytSR Two-Component Regulatory System in Adaptation to Cationic Antimicrobial Peptides in Staphylococcus aureus

Abstract

ABSTRACTMany host defense cationic antimicrobial peptides (HDPs) perturb the staphylococcal cell membrane (CM) and alter transmembrane potential (ΔΨ) as key parts of their lethal mechanism. Thus, a sense-response system for detecting and mediating adaptive responses to such stresses could impact organism survival; theStaphylococcus aureusLytSR two-component regulatory system (TCRS) may serve as such a ΔΨ sensor. One well-known target of this system is thelrgABoperon, which, along with the relatedcidABCoperon, has been shown to be a regulator in the control of programmed cell death and lysis. We used an isogenic set ofS. aureusstrains: (i) UAMS-1, (ii) its isogenic ΔlytSand ΔlrgABmutants, and (iii) plasmid-complemented ΔlytSRand ΔlrgABmutants. The ΔlytSstrain displayed significantly increasedin vitrosusceptibilities to all HDPs tested (neutrophil-derived human neutrophil peptide 1 [hNP-1], platelet-derived thrombin-induced platelet microbicidal proteins [tPMPs], and the tPMP-mimetic peptide RP-1), as well as to calcium-daptomycin (DAP), a cationic antimicrobial peptide (CAP). In contrast, the ΔlrgABstrain exhibited no significant changes in susceptibilities to these cationic peptides, indicating that althoughlytSRpositively regulates transcription oflrgAB, increased HDP/CAP susceptibilities in the ΔlytSmutant werelrgABindependent. Further, parental UAMS-1 (but not the ΔlytSmutant) became more resistant to hNP-1 and DAP following pretreatment with carbonyl cyanidem-chlorophenylhydrazone (CCCP) (a CM-depolarizing agent). Of note,lytSR-dependent survival against CAP/HDP killing was not associated with changes in either surface positive charge, expression ofmprFanddlt, or CM fluidity. The ΔlytSstrain (but not the ΔlrgABmutant) displayed a significant reduction in target tissue survival in an endocarditis model during DAP treatment. Collectively, these results suggest that thelytSRTCRS plays an important role in adaptive responses ofS. aureusto CM-perturbing HDPs/CAPs, likely by functioning as a sense-response system for detecting subtle changes in ΔΨ.