Role of SarA in Virulence Determinant Production and Environmental Signal Transduction in Staphylococcus aureus

Abstract

The staphylococcal accessory regulator (encoded by sarA) is an important global regulator of virulence factor biosynthesis in Staphylococcus aureus. To further characterize its role in virulence determinant production, an sarA knockout mutant was created by insertion of a kanamycin antibiotic resistance cassette into the sarA gene. N-terminal sequencing of exoproteins down-regulated by sarA identified several putative proteases, including a V8 serine protease and a novel metalloprotease, as the major extracellular proteins repressed by sarA. In kinetic studies, the sarA mutation delays the onset of ␣-hemolysin (encoded by hla) expression and reduces levels of hla to approximately 40% of the parent strain level. Furthermore, SarA plays a role in signal transduction in response to microaerobic growth since levels of hla were much lower in a microaerobic environment than after aerobic growth in the sarA mutant. An exoprotein exhibiting hemolysin activity on sheep blood, and up-regulated by sarA independently of the accessory gene regulator (encoded by agr), was specifically induced microaerobically. Transcriptional gene fusion and Western analysis revealed that sarA up-regulates both toxic shock syndrome toxin 1 gene (tst) expression and staphylococcal enterotoxin B production, respectively. This study demonstrates the role of sarA as a signal transduction regulatory component in response to aeration stimuli and suggests that sarA functions as a major repressor of protease activity. The possible role of proteases as regulators of virulence determinant stability is discussed.

Virulence regulation inStaphylococcus aureus: the need for in vivo analysis of virulence factor regulation

“…Expression of agr RNAIII was dramatically repressed in vivo, despite the expression of secreted virulence factors and clinical symptoms of TSS in the animals. Analysis of the transcription profiles showed no correlation between agr expression and the SarA agr P2, agr P3 [7,9,11,12], spa, hla [17] agr P2-P3 [11,12], spa, hla [17] " RNAII, RNAIII [9], # sarS [19], # sarT [22] " arlRS [32] # a-hemolysin, protease activity [8], V8 protease, metalloprotease [15], " glycerol ester hydrolase, lipase, immunodominant antigen A, bhemolysin, # aureolysins, staphylokinase, staphopain, format tetrahydrofolate lyase [16] SarS (SarH1) spa [20] " spa, # hla [19] " spa [20] " protein A [20] SarR sarA P1, P2, and P3 [21] sarA P1 and P2 [21] SarT " proteolytic activity, serine protease activity [30], # a-and b-hemolysin, lipase, coagulase serine protease, protein A [32] MgrA # hla, spa, " cap8, nuc [33] # a-hemolysin, protein A, protease, coagulase, " CP8, nuclease [33] SvrA " hla, spa, RNAII, RNAIII [4] expression of the virulence factors examined. Analysis of an agr mutant strain showed that disruption of the agr locus had only minimal effect on the expression of virulence factors in vivo.…”

“…SarA also regulates virulence factors in a manner that is independent of its effect on agr expression. SarA down-regulates several proteases and activates a-hemolysin (hla), TSST-1, and staphylococcal enterotoxin B (SEB) expression [15]. Two-dimensional gel electrophoresis and protein identification studies showed that SarA also regulated the exoproteins b-hemolysin (hlb), glycerolester hydrolase, autolysin, aureolysin, staphylokinase, staphopain and format tetrahydrofolate lyase [16].…”

Regulation of virulence determinants in vitro and in vivo inStaphylococcus aureus

“…The transition from exponential to postexponential protein expression has been shown to be coordinately controlled by global regulators such as sarA and agr [9] (Table 1) [8,10]. The sarA locus encodes a 372-bp open reading frame with three upstream promoters driving three overlapping transcripts, each coding for the 14.5-kDa SarA protein [11].…”

Genome-scale transcriptional profiling inStaphylococcus aureus : bringing order out of chaos

“…However, other studies have concluded that the impact of SarA on the ability to bind fibronectin is an indirect effect associated with the increased production of proteases in sarA mutants (Chien et al, 1998;Wolz et al, 2000;Karlsson et al, 2001;Blevins et al, 2002;Roberts et al, 2006;Cheung et al, 2008). In the case of hla, mutation of sarA results in decreased transcription in RN6390 but increased transcription in UAMS-1 (Chan & Foster, 1998;Chien et al, 1998;Wolz et al, 2000;Dunman et al, 2001;Karlsson et al, 2001;Blevins et al, 2002;Cassat et al, 2006;Roberts et al, 2006;Cheung et al, 2008), and it was recently proposed that this disparate effect may also revolve around the tcaR mutation in 8325-4 strains like RN6390 and its impact on expression of sarS (Oscarsson et al, 2006).…”