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Staphylococcus aureus svrA: a gene required for virulence and expression of the agr locus^c

Centre for Molecular Microbiology and Infection, Imperial College of Science Technology and Medicine, The Flowers Building, Armstrong Road, London SW7 2AZ, UK¹

Author for correspondence: David W. Holden. Tel: +44 207 594 3073. Fax: +44 207 594 3076. e-mail: d.holden{at}ic.ac.uk

A Staphylococcus aureus gene originally identified by signature-tagged mutagenesis as being required for virulence was cloned, sequenced and named svrA. Hydropathy profiles revealed that SvrA is likely to be membrane associated, having two regions with six membrane-spanning domains, the regions separated by an extended hydrophilic loop. When compared with the wild-type strain, an svrA mutant expressed greatly reduced amounts of -, ß- and -toxins and an increased amount of protein A. Toxin production by the mutant strain was restored to wild-type levels when complemented with a plasmid expressing the svrA gene. Northern hybridization with probes specific for hla (encoding -toxin) and spa (encoding protein A) showed that the svrA mutant strain was affected in the transcription of these genes. svrA mRNA was present in wild-type and agr strains, but agr mRNA and RNAIII were absent in the svrA mutant strain. Virulence studies suggested that the attenuation of the svrA mutant was probably due to its direct or indirect effect on the agr regulon. These results indicate that svrA is required for the expression of agr and RNAIII transcripts and is therefore a new component of the agr regulatory network controlling virulence gene expression in S. aureus.

Keywords: Gram-positive, pathogenesis, gene regulation

Abbreviations: Amp, ampicillin; Cm, chloramphenicol; Erm, erythromycin; GFP, green fluorescent protein; STM, signature-tagged mutagenesis

^c The GenBank accession numbers for the svrA gene are SAV0334 (S. aureus subsp. aureus Mu50) and SA0323 (S. aureus subsp. aureus N315).

^a These authors contributed equally to this work.

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