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

Abstract

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 α-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.