Characterization of RelA inAcinetobacter baumannii

Abstract

ABSTRACTIn response to nutrient depletion, the RelA and SpoT proteins generate the signaling molecule (p)ppGpp, which then controls a number of downstream effectors to modulate cell physiology. InAcinetobacter baumanniistrain AB5075, arelAortholog (ABUW_3302) was identified by a transposon insertion that conferred an unusual colony phenotype. An in-frame deletion inrelA(ΔrelA) failed to produce detectable levels of ppGpp when amino acid starvation was induced with serine hydroxamate. The ΔrelAmutant was blocked from switching from the virulent opaque colony variant (VIR-O) to the avirulent translucent colony variant (AV-T), but the rate of AV-T to VIR-O switching was unchanged. In addition, the ΔrelAmutation resulted in a pronounced hypermotile phenotype on 0.35% agar plates. This hypermotility was dependent on the activation of a LysR regulator ABUW_1132, which was required for expression of AbaR, a LuxR family quorum-sensing regulator. In the ΔrelAmutant, ABUW_1132 was also required for the increased expression of an operon composed of theABUW_3766-ABUW_3773genes required for production of the surfactant-like lipopeptide acinetin 505. Additional phenotypes identified in the ΔrelAmutant included (i) cell elongation at high density, (ii) reduced formation of persister cells tolerant to colistin and rifampin, and (iii) decreased virulence in aGalleria mellonellamodel.IMPORTANCEAcinetobacter baumanniiis a pathogen of worldwide importance. Due to the increasing prevalence of antibiotic resistance, these infections are becoming increasingly difficult to treat. New therapies are required to combat multidrug-resistant isolates. The role of RelA inA. baumanniiis largely unknown. This study demonstrates that like in other bacteria, RelA controls a variety of functions, including virulence. Strategies to inhibit the activity of RelA and the resulting production of ppGpp could inhibit virulence and may represent a new therapeutic approach.