FarRRegulates thefarAB-Encoded Efflux Pump ofNeisseriagonorrhoeaevia an MtrR RegulatoryMechanism

Abstract

The farAB operon of Neisseria gonorrhoeae encodes an efflux pump which mediates gonococcal resistance to antibacterial fatty acids. It was previously observed that expression of the farAB operon was positively regulated by MtrR, which is a repressor of the mtrCDE-encoded efflux pump system (E.-H. Lee and W. M. Shafer, Mol. Microbiol. 33:839-845, 1999). This regulation was believed to be indirect since MtrR did not bind to the farAB promoter. In this study, computer analysis of the gonococcal genome sequence database, lacZ reporter fusions, and gel mobility shift assays were used to elucidate the regulatory mechanism by which expression of the farAB operon is modulated by MtrR in gonococci. We identified a regulatory protein belonging to the MarR family of transcriptional repressors and found that it negatively controls expression of farAB by directly binding to the farAB promoter. We designated this regulator FarR to signify its role in regulating the farAB operon. We found that MtrR binds to the farR promoter, thereby repressing farR expression. Hence, MtrR regulates farAB in a positive fashion by modulating farR expression. This MtrR regulatory cascade seems to play an important role in adjusting levels of the FarAB and MtrCDE efflux pumps to prevent their excess expression in gonococci.

MtrR Modulates rpoH Expression and Levels of Antimicrobial Resistance in Neisseria gonorrhoeae

“…Electrophoretic mobility shift assays (EMSAs) using purified MBP fused to MtrR were performed as previously described (5,6,15). In brief, the 184-bp promoter region of rpoH lacking the leader sequence was amplified by PCR using 5ЈPrpoH and 3ЈPrpoHB from strain JF14 ( Table 1).…”

“…DNA-binding proteins such as MtrR that negatively regulate bacterial efflux pump genes have been considered to be "local" gene regulators, although there is increasing evidence that they can directly or indirectly influence the expression of other genes (6,15). In order to define the genes in gonococci regulated by MtrR, we employed a microarray analysis of total RNA extracted from mid-logarithmic-phase broth cultures of isogenic MtrR-positive and MtrR-negative gonococci.…”

Towards an Understanding of Chromosomally Mediated Penicillin Resistance in Neisseria gonorrhoeae : Evidence for a Porin-Efflux Pump Collaboration

“…It is now clear that MtrR can regulate genes other than mtrCDE (4,9), and a complete understanding of the mtrR regulon should help in testing the model described above. This is particularly true if MtrR-regulated genes are important in determining levels of antibiotic resistance through a penBdependent process; there is no evidence, however, that expression of mtrR influences levels of PorB (or the allelic PorA).…”

The Role of the Transcription Factors MtrR and MtrA in the Fitness of the Pathogen Neisseria gonorrhoeae

“…The simplest explanation for the incomplete restoration of these in vitro phenotypes is the possibility that mtrR expression from a site distant from the mtrCDE locus may not be the same as that which occurs in its native site. However, considering the fact that MtrR acts on other loci besides mtrCDE (47,48,96), these results also raised the possibility that targets of MtrR other than the MtrC-MtrD-MtrE pump may contribute to the fitness advantage demonstrated by the mtrR mutant in vivo.…”

“…This hypothesis must be carefully tested because MtrR directly or indirectly regulates other genes that may playa role in pathogenesis, including mtrF (48), the farAB operon (48,96), pilM, and ponA (47). Additionally, the importance of the activator protein MtrA, which belongs to the AraC-type family of activators, must be considered.…”