The Two-Component System GrvRS (EtaRS) Regulates ace Expression in Enterococcus faecalis OG1RF

Abstract

e Expression of ace (adhesin to collagen of Enterococcus faecalis), encoding a virulence factor in endocarditis and urinary tract infection models, has been shown to increase under certain conditions, such as in the presence of serum, bile salts, urine, and collagen and at 46°C. However, the mechanism of ace/Ace regulation under different conditions is still unknown. In this study, we identified a two-component regulatory system GrvRS as the main regulator of ace expression under these stress conditions. Using Northern hybridization and ␤-galactosidase assays of an ace promoter-lacZ fusion, we found transcription of ace to be virtually absent in a grvR deletion mutant under the conditions that increase ace expression in wild-type OG1RF and in the complemented strain. Moreover, a grvR mutant revealed decreased collagen binding and biofilm formation as well as attenuation in a murine urinary tract infection model. Here we show that GrvR plays a major role in control of ace expression and E. faecalis virulence. Enterococcus faecalis is a Gram-positive commensal bacterium of the gastrointestinal tract and also a common cause of hospital-acquired infections and endocarditis (1). During experimental infections, the adhesin to collagen of E. faecalis (Ace) plays an important role which has been attributed to mediating binding of E. faecalis to human extracellular matrix (ECM) proteins such as collagen (types I and IV), laminin, and dentin (2-4). Different infection models have shown attenuation of ace deletion mutants (5-7) and specific anti-recombinant Ace (rAce) antibodies were shown to confer protection against E. faecalis infection in an experimental endocarditis model (6). Therefore, Ace is considered a virulence factor in E. faecalis infection.In order to better understand the role of Ace, it is important to study the regulation mechanisms of ace expression and surface display. Previous works have identified several environmental factors regulating ace expression; e.g., transcription of ace was increased when E. faecalis was grown at 46°C and grown in the presence of 40% horse serum, urine, and bile salts (5,8,9). In addition, levels of Ace on the cell surface are dependent on the E. faecalis strain and growth phase (10-12). With E. faecalis OG1RF, Ace is increased in the early exponential phase but reduced in the stationary phase; however, with E. faecalis JH2-2, it is maintained in later growth phases (10-12). The decrease in stationary-phase Ace in strain OG1RF was shown to be dependent on a functional fsr quorum-sensing system controlling the expression of gelatinase (GelE), which cleaves Ace from the OG1RF cell surface in latephase cultures (11). Strains such as JH2-2 (lacking a complete fsr system operon) as well as fsr and gelE mutants of OG1RF do not cleave Ace from the surface (11), since they do not produce gelatinase. In other words, the amount of Ace on OG1RF strains is regulated in part at the posttranslational level. At the transcriptional level, the enterococcal regulator of survival (Ers) was prev...

Expression of Adhesive Pili and the Collagen-Binding Adhesin Ace Is Activated by ArgR Family Transcription Factors in Enterococcus faecalis

“…However, these studies were carried out in the unrelated strain JH2-2. A more recent study (38) indicated that the deletion of the ers gene did not affect ace expression in OG1RF; instead, these investigators found that GvrR, a response regulator protein encoded by the gvrRS two-component genes, activated ace transcription. They also found that GvrR activation of ace occurred in organisms grown at 46°C and in the presence of serum, whereas all our experiments employed cultures grown at 37°C in the absence of serum; since several previous studies focused on protein expression, the temperature effects could be posttranscriptional.…”

Gram-Positive Uropathogens, Polymicrobial Urinary Tract Infection, and the Emerging Microbiota of the Urinary Tract

“…Ace is regulated by the GrvRS two-component regulatory system and, accordingly, gvrR mutants are attenuated for biofilm formation in vitro and for virulence in a murine model of ascending UTI [140]. The ArgR family transcription factor AhrC is important for early biofilm formation in vitro, and ahrC mutans are significantly attenuated for biofilm growth on catheters as well as for bladder and kidney colonization during CAUTI [141].…”

Gram-Positive Uropathogens, Polymicrobial Urinary Tract Infection, and the Emerging Microbiota of the Urinary Tract

“…Additional E. faecalis surface proteins that contribute to urovirulence in animal models include the collagen adhesin Ace and the enterococcal fibronectin binding protein EfbA [ 28 , 138 , 139 ]. Ace is regulated by the GrvRS two-component regulatory system and, accordingly, gvrR mutants are attenuated for biofilm formation in vitro and for virulence in a murine model of ascending UTI [ 140 ]. The ArgR family transcription factor AhrC is important for early biofilm formation in vitro, and ahrC mutans are significantly attenuated for biofilm growth on catheters as well as for bladder and kidney colonization during CAUTI [ 141 ].…”