Strain-Dependent Differences in the Regulatory Roles of sarA and agr in Staphylococcus aureus

Abstract

The accessory gene regulator (agr) and the staphylococcal accessory regulator (sar) are central regulatory elements that control the production of Staphylococcus aureus virulence factors. To date, the functions of these loci have been defined almost exclusively using RN6390, which is representative of the laboratory strain 8325-4. However, RN6390 was recently shown to have a mutation in rsbU that results in a phenotype resembling that of a sigB mutant (I. Kullik et al., J. Bacteriol. 180:4814-4820, 1998). For that reason, it remains unclear whether the regulatory events defined in RN6390 are representative of the events that take place in clinical isolates of S. aureus. To address this issue, we generated mutations in the sarA and agr loci of three laboratory strains (RN6390, Newman, and S6C) and four clinical isolates (UAMS-1, UAMS-601, DB, and SC-1). Mutation of sarA in the cna-positive strains UAMS-1 and UAMS-601 resulted in an increased capacity to bind collagen, while mutation of agr had little impact. Northern blot analysis confirmed that the increase in collagen binding was due to increased cna transcription. Without exception, mutation of sarA resulted in increased production of proteases and a decreased capacity to bind fibronectin. Mutation of agr had the opposite effect. Although mutation of sarA resulted in a slight reduction in fnbA transcription, changes in the ability to bind fibronectin appeared to be more directly correlated with changes in protease activity. Lipase production was reduced in both sarA and agr mutants. While mutation of sarA in RN6390 resulted in reduced hemolytic activity, it had the opposite effect in all other strains. There appeared to be reduced levels of the sarC transcript in RN6390, but there was no difference in the overall pattern of sar transcription or the production of SarA. Although mutation of sarA resulted in decreased RNAIII transcription, this effect was not evident under all growth conditions. Taken together, these results suggest that studies defining the regulatory roles of sarA and agr by using RN6390 are not always representative of the events that occur in clinical isolates of S. aureus.Staphylococcus aureus is an opportunistic pathogen capable of causing a wide variety of infections. Its pathogenic diversity is due to its ability to produce a diverse array of virulence factors. These factors fall into two groups based on whether they remain associated with the cell surface or are exported into the extracellular milieu. In vitro, these two groups are globally and inversely regulated, with the surface proteins being produced during the exponential growth phase and the exoproteins being produced as cultures enter postexponential growth (33). This is consistent with the fact that the production of S. aureus virulence factors is responsive to a quorum-sensing signal (27). This signal exerts its regulatory effects through a two-component signal transduction system encoded by the accessory gene regulator (agr). Induction of agr results in increased expression of...

Transcriptional profiling of a Staphylococcus aureus clinical isolate and its isogenic agr and sarA mutants reveals global differences in comparison to the laboratory strain RN6390

“…We have previously demonstrated that RN6390 expresses RNAIII at elevated levels in comparison to UAMS-1 , and our microarray analysis confirmed that RN6390 expressed an increased level of the hld, agrA and agrB transcripts in the exponential growth phase in comparison to UAMS-1 (Table 3) (the agrC and agrD genes were not identified as upregulated in RN6390 versus UAMS-1 because the two strains possess different agr subtypes; Blevins et al, 2002). The hld transcript, which is included within the RNAIII effector molecule of the agr system (Janzon et al, 1989), was upregulated 9?4-fold within RN6390 relative to UAMS-1, in the exponential growth phase.…”

SarA Positively Controls Bap-Dependent Biofilm Formation in Staphylococcus aureus

“…In this study, we evaluated the regulation of the factor Bap by the global regulators agr and sarA. Examination of bap mRNA production by different strains at various growth phases showed that sarA was ences in the regulatory roles of sarA and agr in S. aureus (6). Another plausible explanation may be that spontaneous mutations in global regulator genes may occur in some isolates of S. aureus as has been found in S. epidermidis (42,43, and our unpublished results).…”

VfrB Is a Key Activator of the Staphylococcus aureus SaeRS Two-Component System

“…Similar to saeRS mutants (28), vfrB mutants show a marked reduction in Hla-dependent hemolytic activity when grown on rabbit blood agar, demonstrating decreased ability to produce Hla, and have enhanced production of V8 protease (26). Hla is under the control of multiple transcriptional and posttranscriptional factors (29)(30)(31)(32)(33)(34). Since Sae is known to be a major contributor to hla expression, we sought to determine whether changes in Hla activity in response to VfrB are in the same pathway as SaeRS or in independent pathways.…”

“…An additional explanation for this discrepancy in the necessity of VfrB for class I and class II promoters is that class I promoters have two SaeR-binding sites, whereas class II promoters have a single SaeR-binding site (14); therefore, higher levels of phosphorylated SaeR are required to activate class I promoters. Finally, in addition to the regulation of hla by SaeRS, several other master regulatory factors (e.g., Agr, RNAIII, Rot, SarA, and SarT) influence transcription of the hemolysin (29)(30)(31)(32)(33)(34), adding additional levels of regulation that affect expression. Thus, it is plausible that the complex regulatory mechanisms that control hla expression also contribute to VfrB having less effect on this class II gene than on coa.…”