ABSTRACT
Staphylococcus aureus
is a formidable human pathogen that uses secreted cytolytic factors to injure immune cells and promote infection of its host. Of these proteins, the bicomponent family of pore-forming leukocidins play critical roles in
S. aureus
pathogenesis. The regulatory mechanisms governing the expression of these toxins are incompletely defined. In this work, we performed a screen to identify transcriptional regulators involved in leukocidin expression in
S. aureus
strain USA300. We discovered that a metabolic sensor-regulator, RpiRc, is a potent and selective repressor of two leukocidins, LukED and LukSF-PV. Whole-genome transcriptomics,
S. aureus
exoprotein proteomics, and metabolomic analyses revealed that RpiRc influences the expression and production of disparate virulence factors. Additionally, RpiRc altered metabolic fluxes in the trichloroacetic acid cycle, glycolysis, and amino acid metabolism. Using mutational analyses, we confirmed and extended the observation that RpiRc signals through the accessory gene regulatory (Agr) quorum-sensing system in USA300. Specifically, RpiRc represses the
rnaIII
promoter, resulting in increased repressor of toxins (Rot) levels, which in turn negatively affect leukocidin expression. Inactivation of
rpiRc
phenocopied
rot
deletion and increased
S. aureus
killing of primary human polymorphonuclear leukocytes and the pathogenesis of bloodstream infection
in vivo.
Collectively, our results suggest that
S. aureus
senses metabolic shifts by RpiRc to differentially regulate the expression of leukocidins and to promote invasive disease.
IMPORTANCE
The bicomponent pore-forming leukocidins play pivotal roles in the ability of
S. aureus
to kill multiple host immune cells, thus enabling this pathogen to have diverse tissue- and species-tropic effects. While the mechanisms of leukocidin-host receptor interactions have been studied in detail, the regulatory aspects of leukocidin expression are less well characterized. Moreover, the expression of the leukocidins is highly modular
in vitro
, suggesting the presence of regulators other than the known Agr, Rot, and
S. aureus
exoprotein pathways. Here, we describe how RpiRc, a metabolite-sensing transcription factor, mediates the repression of two specific leukocidin genes,
lukED
and
pvl
, which in turn has complex effects on the pathogenesis of
S. aureus
. Our findings highlight the intricacies of leukocidin regulation by
S. aureus
and demonstrate the involvement of factors beyond traditional virulence factor regulators.
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