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Journal of Bacteriology, May 2005, p. 3028-3038, Vol. 187, No. 9
0021-9193/05/$08.00+0     doi:10.1128/JB.187.9.3028-3038.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Role of HtrA in Growth and Competence of Streptococcus mutans UA159

Sang-Joon Ahn, José A. C. Lemos, and Robert A. Burne*

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

Received 21 September 2004/ Accepted 27 January 2005

We report here that HtrA plays a role in controlling growth and competence development for genetic transformation in Streptococcus mutans. Disruption of the gene for HtrA resulted in slow growth at 37°C, reduced thermal tolerance at 42°C, and altered sucrose-dependent biofilm formation on polystyrene surfaces. The htrA mutant also displayed a significantly reduced ability to undergo genetic transformation. A direct association between HtrA and genetic competence was demonstrated by the increased expression of the htrA gene upon exposure to competence-stimulating peptide. The induction of htrA gradually reached a maximum at around 20 min, suggesting that HtrA may be involved in a late competence response. Complementation of the htrA mutation in a single copy on the chromosome of the mutant could rescue the defective growth phenotypes but not transformability, apparently because a second gene, spo0J, immediately downstream of htrA, also affects transformation. The htrA and spo0J genes were shown to be both individually transcribed and cotranscribed and probably have a functional connection in competence development. HtrA regulation appears to be finely tuned in S. mutans, since strains containing multiple copies of htrA exhibited abnormal growth phenotypes. Collectively, the results reveal HtrA to be an integral component of the regulatory network connecting cellular growth, stress tolerance, biofilm formation, and competence development and reveal a novel role for the spo0J gene in genetic transformation.

* Corresponding author. Mailing address: Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL 32610. Phone: (352) 846-2520. Fax: (352) 392-7357. E-mail: rburne{at}ufl.edu.

Journal of Bacteriology, May 2005, p. 3028-3038, Vol. 187, No. 9
0021-9193/05/$08.00+0     doi:10.1128/JB.187.9.3028-3038.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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