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Microbiology 155 (2009), 2856-2865; DOI  10.1099/mic.0.028456-0
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Microbiology 155 (2009), 2856-2865; DOI  10.1099/mic.0.028456-0
© 2009 Society for General Microbiology

Expression of the Streptococcus mutans essential two-component regulatory system VicRK is pH and growth-phase dependent and controlled by the LiaFSR three-component regulatory system

Yannick D. N. Tremblay1,2, Henry Lo1, Yung-Hua Li1,3, Scott A. Halperin1,2,4 and Song F. Lee1,2,3,4

1 Department of Microbiology and Immunology, Faculty of Medicine, Dalhousie University, Halifax, NS, Canada
2 Canadian Center for Vaccinology, Dalhousie University and the IWK Health Center, Halifax, NS, Canada
3 Department of Applied Oral Sciences, Faculty of Dentistry, Dalhousie University, Halifax, NS, Canada
4 Department of Pediatrics, Dalhousie University, Halifax, NS, Canada

As an inhabitant of the human oral cavity, Streptococcus mutans faces frequent environmental changes. Two-component regulatory systems (TCSs) play a critical role in responding to these changes. Recently, an essential TCS, VicRKX, has been identified. The objective of this study was to identify the environmental signal and bacterial factors regulating the expression of the vicRKX operon. The promoter of the vicRKX operon was fused to a promoterless lacZ reporter gene and introduced into S. mutans UA159. LacZ plate assay identified pH, vancomycin, ampicillin, penicillin G and polymyxin B, but not carbohydrates, as factors affecting expression. Using RNA dot-blotting, high levels of vicR transcript were observed in cells at the mid- and late-exponential phase of growth and in cells grown in media buffered at pH 7.8. Given that vicR expression was pH-dependent, the genes encoding a putative pH-sensing three-component regulatory system (LiaFSR) were deleted. The liaS mutant exhibited upregulation of vicR regardless of the growth condition. The role of VicK, VicX, and the competence-signal peptide (CSP) was also investigated; the results showed that vicR expression was not autoregulated and was downregulated by the CSP in a ComX-independent manner. In conclusion, the expression of vicRKX is influenced by culture pH, growth phase and antibiotic stress, and is regulated by LiaFRS.

Correspondence
Song F. LeeSong.Lee@Dal.Ca

Abbreviations: CSP, competence-stimulating peptide; TCS, two-component system






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