RpiRc Is a Pleiotropic Effector of Virulence Determinant Synthesis and Attenuates Pathogenicity in Staphylococcus aureus

Abstract

fIn Staphylococcus aureus, metabolism is intimately linked with virulence determinant biosynthesis, and several metabolite-responsive regulators have been reported to mediate this linkage. S. aureus possesses at least three members of the RpiR family of transcriptional regulators. Of the three RpiR homologs, RpiRc is a potential regulator of the pentose phosphate pathway, which also regulates RNAIII levels. RNAIII is the regulatory RNA of the agr quorum-sensing system that controls virulence determinant synthesis. The effect of RpiRc on RNAIII likely involves other regulators, as the regulators that bind the RNAIII promoter have been intensely studied. To determine which regulators might bridge the gap between RpiRc and RNAIII, sarA, sigB, mgrA, and acnA mutations were introduced into an rpiRc mutant background, and the effects on RNAIII were determined. Additionally, phenotypic and genotypic differences were examined in the single and double mutant strains, and the virulence of select strains was examined using two different murine infection models. The data suggest that RpiRc affects RNAIII transcription and the synthesis of virulence determinants in concert with B , SarA, and the bacterial metabolic status to negatively affect virulence. Staphylococcus aureus is a major human pathogen causing a diverse range of infections, from superficial skin and wound infections to life-threatening diseases such as bacteremia, endocarditis, osteomyelitis, deep tissue abscesses, or pneumonia (1). The pathogenicity of S. aureus is due in part to its ability to produce a large number of virulence determinants, including secreted proteins (e.g., toxins and proteases), cell wall-associated proteins (e.g., protein A and fibronectin binding proteins), and extracellular polysaccharides (i.e., capsule and polysaccharide intercellular adhesion). During colonization and infection of a host, S. aureus must adapt to rapidly changing environmental and nutritional conditions by coordinating the transcription and translation of physiologic and virulence genes (2). To coordinately control these cellular processes, S. aureus has evolved or acquired a network of regulators such as the recently identified family of proteins, RpiR, that affect pentose phosphate pathway activity and virulence determinant synthesis (3).Central to the regulatory network is the accessory gene regulator (Agr) system, a regulator of virulence determinant synthesis that responds to the bacterial population density (4). The agr locus consists of two divergent transcriptional units, RNAII and RNAIII, driven by the P2 and P3 promoters, respectively. RNAII comprises the agrBDCA operon, of which the agrBD gene products are involved in the synthesis, transport, and maturation of an autoinducing peptide (AIP). As the cell density increases, AIP accumulates in the extracellular milieu and when a threshold is achieved the two-component system AgrCA responds by activating transcription of both P2 and P3 promoters. The P3 promoter drives transcription of RNAIII, which is the re...

RpiRc regulates RsbU to modulate eDNA-dependent biofilm formation andin vivovirulence ofStaphylococcus aureusin a mouse model of catheter infection

“…Sbi is a pro-inflammatory staphylococcal antigen (94) and both forms contribute to S. aureus immune evasion (phagocytosis and Neutrophil killing) (93). In addition to the increased protease and hemolysins production observed, decreased production of Sbi in JE2 Δ rpiRc would suggest increased virulence for this mutant in vivo as previously observed in two in vivo mouse models of abscess and pneumonia using planktonic bacteria (75, 76).…”

“…They interact together and are all involved in the production or inhibition of extracellular proteins, regulating biofilm matrix stability. A previous publication showed that under planktonic growth conditions, RpiRc positively regulated all these factors (75). The laboratory strain SA113 contains a point mutation in rsbU , the regulator of SigB activity.…”

“…Using the recently available Nebraska Transposon Library, a new actor in the regulation of eDNA and biofilm formation of S. aureus could be identified. RpiRc is an enzyme involved in the pentose phosphate pathway (PPP), identified by homology from E. coli (75). It was first described in S. aureus as a regulator of RNAIII and virulence under planktonic conditions in vitro and in vivo respectively (75, 76).…”

“…RpiRc is an enzyme involved in the pentose phosphate pathway (PPP), identified by homology from E. coli (75). It was first described in S. aureus as a regulator of RNAIII and virulence under planktonic conditions in vitro and in vivo respectively (75, 76). PPP starts from G6P to produce ribose required for nucleic acid synthesis.…”

“…RsbU deletion in other strains than SA113 confirmed results observed in this laboratory strain, RpiRc is involved in RsbU regulation to control biofilm formation and eDNA production/turn over in mature biofilms. An interaction between RpiRc and RsbU was previously suggested without phenotypic information (75, 76). From a review of the literature, this is the first report on RsbU directly involved in the regulation of eDNA amounts in mature S. aureus biofilms.…”