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Infection and Immunity, October 2007, p. 5011-5017, Vol. 75, No. 10
0019-9567/07/$08.00+0     doi:10.1128/IAI.01824-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Role for sagA and siaA in Quorum Sensing and Iron Regulation in Streptococcus pyogenes{triangledown}

Kowthar Y. Salim,1 Joyce C. de Azavedo,2 Darrin J. Bast,2 and Dennis G. Cvitkovitch1*

Department of Microbiology, Dental Research Institute, University of Toronto, Ontario, Canada,1 Department of Laboratory Medicine and Pathobiology, University of Toronto, Ontario, Canada2

Received 16 November 2006/ Returned for modification 3 April 2007/ Accepted 10 July 2007

Streptococcus pyogenes is a ubiquitous and versatile pathogen that causes 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 and siaA (also referred to as pel and htsA, respectively), in response to conditions of varying cell densities and iron concentrations. The sagA gene was up-regulated in conditioned medium from a wild-type strain but not from sagA-deficient mutants, and the gene was also up-regulated in the presence of streptolysin S (SLS), the gene product of sagA, thus indicating that this gene or its product is involved in density-dependent regulation of S. pyogenes. By comparison, siaA responded in a manner consistent with a role in iron acquisition since it was up-regulated under iron-restricted conditions. Although siaA expression was also up-regulated in the presence of SLS and in conditioned media from both wild-type and sagA-deficient mutants, this up-regulation was not growth phase dependent. We conclude that sagA encodes a quorum-sensing signaling molecule, likely SLS, and further support the notion that siaA is likely involved in iron acquisition.

* Corresponding author. Mailing address: University of Toronto, Dental Research Institute, Department of Microbiology, Rm. 449A, 124 Edward Street, Toronto, Ontario, Canada M5G 1G6. Phone: (416) 979-4917. Fax: (416) 979-4936. E-mail: d.cvitkovitch{at}dentistry.utoronto.ca

{triangledown} Published ahead of print on 16 July 2007.

Editor: V. J. DiRita

Infection and Immunity, October 2007, p. 5011-5017, Vol. 75, No. 10
0019-9567/07/$08.00+0     doi:10.1128/IAI.01824-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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