The Staphylococcus aureus ArlRS two‐component system regulates virulence factor expression through MgrA

Summary The Gram‐positive bacterium, Staphylococcus aureus, is a versatile pathogen that can sense and adapt to a wide variety of environments within the human host, in part through its 16 two‐component regulatory systems. The ArlRS two‐component system has been shown to affect many cellular processes in S. aureus, including autolysis, biofilm formation, capsule synthesis and virulence. Yet the molecular details of this regulation remained largely unknown. We used RNA sequencing to identify the ArlRS regulon, and found 70% overlap with that of the global regulator MgrA. These genes included cell wall‐anchored adhesins (ebh, sdrD), polysaccharide and capsule synthesis genes, cell wall remodeling genes (lytN, ddh), the urease operon, genes involved in metal transport (feoA, mntH, sirA), anaerobic metabolism genes (adhE, pflA, nrdDG) and a large number of virulence factors (lukSF, lukAB, nuc, gehB, norB, chs, scn and esxA). We show that ArlR directly activates expression of mgrA and identify a probable ArlR‐binding site (TTTTCTCAT‐N4‐TTTTAATAA). A highly similar sequence is also found in the spx P2 promoter, which was recently shown to be regulated by ArlRS. We also demonstrate that ArlS has kinase activity toward ArlR in vitro, although it has slower kinetics than other similar histidine kinases. Methicillin‐resistant Staphylococcus aureus (MRSA) is a leading cause of bloodstream infections, pneumonia and surgical site infections. One of the hallmarks of S. aureus is its diverse array of virulence factors, such as secreted toxins, cell wall‐anchored adhesins and immune evasion factors. We demonstrate that the ArlRS two‐component system regulates more than 200 genes, including many virulence factors, primarily through controlling expression of the global regulators MgrA and Spx.