The SaeRS Two-Component System Is a Direct and Dominant Transcriptional Activator of Toxic Shock Syndrome Toxin 1 in Staphylococcus aureus

Abstract

Toxic shock syndrome toxin 1 (TSST-1) is a Staphylococcus aureus superantigen that has been implicated in both menstrual and nonmenstrual toxic shock syndrome (TSS). Despite the important role of TSST-1 in severe human disease, a comprehensive understanding of staphylococcal regulatory factors that control TSST-1 expression remains incomplete. The S. aureus exotoxin expression (Sae) operon contains a well-characterized two-component system that regulates a number of important exotoxins in S. aureus, although regulation of TSST-1 by the Sae system has not been investigated. We generated a defined deletion mutant of the Sae histidine kinase sensor (saeS) in the prototypic menstrual TSS strain S. aureus MN8. Mutation of saeS resulted in a complete loss of TSST-1 expression. Using both luciferase reporter experiments and quantitative real-time PCR, we demonstrate that the Sae system is an important transcriptional activator of TSST-1 expression. Recombinant SaeR was able to bind directly to the tst promoter to a region containing two SaeR consensus binding sites. Although the stand-alone SarA transcriptional regulator has been shown to be both a positive and a negative regulator of TSST-1, deletion of sarA in S. aureus MN8 resulted in a dramatic overexpression of TSST-1. As expected, mutation of agr also reduced TSST-1 expression, but this phenotype appeared to be independent of Sae. A double mutation of saeS and sarA resulted in the loss of TSST-1 expression. This work indicates that the Sae system is a dominant and direct transcriptional activator that is required for expression of TSST-1. IMPORTANCEThe TSST-1 superantigen is an exotoxin, produced by some strains of S. aureus, that has a clear role in both menstrual and nonmenstrual TSS. Although the well-characterized agr quorum sensing system is a known positive regulator of TSST-1, the molecular mechanisms that directly control TSST-1 expression are only partially understood. Our studies demonstrate that the Sae two-component regulatory system is a positive transcriptional regulator that binds directly to the TSST-1 promoter, and furthermore, our data suggest that Sae is required for expression of TSST-1. This work highlights how major regulatory circuits can converge to fine-tune exotoxin expression and suggests that the Sae regulatory system may be an important target for antivirulence strategies. Staphylococcus aureus is both a common commensal of humans and a prominent bacterial pathogen that is responsible for an assortment of illnesses ranging from self-limiting superficial infections to life-threatening invasive diseases (1). While most infections caused by S. aureus involve the coordinated expression of numerous virulence factors, a few select diseases, including staphylococcal scalded skin syndrome, food poisoning, and toxic shock syndrome (TSS), require the expression of specific staphylococcal exotoxins (2).Staphylococcal TSS is a rare but devastating disease that is caused by S. aureus strains that secrete high levels of superantigens. Super...

SaeRS Is Responsive to Cellular Respiratory Status and Regulates Fermentative Biofilm Formation in Staphylococcus aureus

“…The binding site sequence differed from the consensus sequence by one guanine and one adenine (36). SaeR binding site sequences in the promoter regions of alternate SaeR regulon members, such as tst and nuc, also differ from the consensus sequence by 2 bp (37,38). Consistent with the in silico prediction, atlA transcript levels were decreased in the ΔsaePQRS strain during fermentative growth ( Fig.…”

The SaeRS Two‐Component System of Staphylococcus aureus

“…The cap gene is activated by Agr but repressed by Sae [19,83,84]. In the case of TSST-1, the toxin responsible for toxic shock syndrome [85], both Agr and Sae are positive regulators [73]. However, the deletion of agr did not abolish the production of TSST-1 whereas sae -deletion did [73].…”

“…In the case of TSST-1, the toxin responsible for toxic shock syndrome [85], both Agr and Sae are positive regulators [73]. However, the deletion of agr did not abolish the production of TSST-1 whereas sae -deletion did [73]. Third, several in vivo model experiments showed that Sae is critical for toxin production whereas Agr is dispensable.…”

“…Moreover, in most studies, the effect of agr mutation on the sae expression was not confirmed by a complementation test [13,14,79]. Recently, Baroja et al showed that, in the strain MN8, the deletion of agr did not affect the transcription of saeR [73], further confirming the independence of Agr and Sae.…”

Regulation of toxic shock syndrome toxin‐1 by the accessory gene regulator in Staphylococcus aureus is mediated by the repressor of toxins

“…However, how Agr regulates TSST‐1 is not known. We recently demonstrated that the S. aureus exotoxin expression (Sae) regulatory operon was a direct and dominant positive regulator of tst transcription, where the SaeR response regulator bound directly to the tst promoter (P tst ) (Baroja et al , ). Conversely, the SarA stand‐alone regulator, which also binds directly to P tst (Andrey et al , ), is a potent repressor of tst expression in the prototype menstrual‐associated TSS strain S. aureus MN8 (Baroja et al , ).…”