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Journal of Bacteriology, April 2009, p. 2153-2162, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01641-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Transcriptional Regulation of the Cellobiose Operon of Streptococcus mutans{triangledown} ,§

Lin Zeng and Robert A. Burne*

Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida 32610

Received 18 November 2008/ Accepted 13 January 2009

The ability of Streptococcus mutans to catabolize cellobiose, a β-linked glucoside generated during the hydrolysis of cellulose, is shown to be regulated by a transcriptional regulator, CelR, which is encoded by an operon with a phospho-β-glucosidase (CelA) and a cellobiose-specific sugar phosphotransferase system (PTS) permease (EIICel). The roles of CelR, EIICel components, and certain fructose/mannose-PTS permeases in the transcriptional regulation of the cel locus were analyzed. The results revealed that (i) the celA and celB (EIIBCel) gene promoters require CelR for transcriptional activation in response to cellobiose, but read-through from the celA promoter contributes to expression of the EIICel genes; (ii) the EIICel subunits were required for growth on cellobiose and for transcriptional activation of the cel genes; (iii) CcpA plays little direct role in catabolite repression of the cel regulon, but loss of specific PTS permeases alleviated repression of cel genes in the presence of preferred carbohydrates; and (iv) glucose could induce transcription of the cel regulon when transported by EIICel. CelR derivatives containing amino acid substitutions for five conserved histidine residues in two PTS regulatory domains and an EIIA-like domain also provided important insights regarding the function of this regulator. Based on these data, a model for the involvement of PTS permeases and the general PTS proteins enzyme I and HPr was developed that reveals a critical role for the PTS in CcpA-independent catabolite repression and induction of cel gene expression in S. mutans.

* Corresponding author. Mailing address: Department of Oral Biology, University of Florida, College of Dentistry, P.O. Box 100424, Gainesville, FL 32610. Phone: (352) 392-4370. Fax: (352) 392-7357. E-mail: rburne{at}dental.ufl.edu

{triangledown} Published ahead of print on 23 January 2009.

§ Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, April 2009, p. 2153-2162, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01641-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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