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Infect. Immun. doi:10.1128/IAI.01824-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Quorum sensing and iron regulation in Streptococcus pyogenes: A role for sagA/pel and siaA/htsA

Department of Microbiology, Dental Research Institute, University of Toronto, ON, Can., Department of Laboratory Medicine and Pathobiology, University of Toronto, ON, Can.

^* To whom correspondence should be addressed. Email: d.cvitkovitch{at}dentistry.utoronto.ca.

	Abstract

Streptococcus pyogenes is a ubiquitous and versatile pathogen causing a variety of infections with a wide range of severity. The versatility of this organism is due in part to its capacity to regulate virulence gene expression in response to the many environments that it encounters during an infection. We analyzed the expression of two potential virulence factors, sagA/pel and siaA/htsA, in response to conditions of varying cell density and iron concentration. The sagA/pel gene was up-regulated in conditioned medium from a wild-type strain but not from sagA/pel-deficient mutants, and was also up-regulated in the presence of streptolysin S (SLS), the gene product of sagA/pel, thus indicating that this gene or its product is involved in density-dependent regulation of S. pyogenes. By comparison, siaA/htsA responded in a manner consistent with a role in iron-acquisition since it was up-regulated under iron-restricted conditions. Although, siaA/htsA expression was also up-regulated in the presence of SLS, and conditioned media from both wild-type and sagA/pel-deficient mutants, this up-regulation was not growth-phase-dependent. We conclude that sagA/pel encodes a quorum sensing signaling molecule, likely SLS, and further support the notion that siaA/htsA is likely involved in iron acquisition.