Cross-regulatory sRNA networks shape adaptive stress responses in Staphylococcus aureus: RsaC and RsaOI regulate galactose metabolism and cell wall homeostasis

Abstract

Staphylococcus aureus is a major human pathogen whose adaptability relies on network of regulators, including two-component systems, transcription factors and small regulatory RNAs. Yet most of these regulators are dispensable for growth, suggesting cooperation or redundancy between them. To explore this hypothesis, we performed a yeast one-hybrid screen of 43 TFs against the promoters of seven sRNAs, which identified 27 novel TF-sRNA promoter interactions. We then focused on three sRNAs. We showed that srn_9342 is repressed by VraR and MntR, which also control rsaOI and rsaC, respectively. We found that rsaC, like rsaOI, is induced by acidic pH and vancomycin exposure, whereas srn_9342 expression remained unchanged. We also demonstrated in vitro that Srn_9342 interacts with both RsaOI and RsaC. Its role toward these two sRNAs remains unknown, but this interaction raises the possibility that it modulates their availability or activity. RsaOI and RsaC both act on the tagatose pathway for galactose utilization, through different genes: lacD for RsaOI, as previously reported, and lacC for RsaC, newly identified here. We showed that both sRNAs are required for surface charge remodeling and for growth under subinhibitory vancomycin. They also modulate the virulence factors PSM and protein A. Both sRNAs reduce PSM production, whereas protein A is decreased by RsaOI, likely through Rot, and increased by RsaC through an unknown, probably indirect mechanism. Together, our results suggest that a single cell wall stress can engage several regulators that could cooperate on shared targets or pathways, which may explain why individual regulators are dispensable.