This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Faustoferri, R. C. Articles by Quivey, R. G. Search for Related Content PubMed PubMed Citation Articles by Faustoferri, R. C. Articles by Quivey, R. G., Jr.

 Previous Article  |  Next Article 

Journal of Bacteriology, April 2005, p. 2705-2714, Vol. 187, No. 8
0021-9193/05/$08.00+0     doi:10.1128/JB.187.8.2705-2714.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Smx Nuclease Is the Major, Low-pH-Inducible Apurinic/Apyrimidinic Endonuclease in Streptococcus mutans

Roberta C. Faustoferri,¹ Kristina Hahn,^2, Kellie Weiss,^1, and Robert G. Quivey Jr.^1,2*

Center for Oral Biology, Aab Institute for Biomedical Sciences,¹ Department of Microbiology and Immunology, University of Rochester, Rochester, New York²

Received 11 November 2004/ Accepted 5 January 2005

The causative agent of dental caries in humans, Streptococcus mutans, outcompetes other bacterial species in the oral cavity and causes disease by surviving acidic conditions in dental plaque. We have previously reported that the low-pH survival strategy of S. mutans includes the ability to induce a DNA repair system that appears to involve an enzyme with exonuclease functions (K. Hahn, R. C. Faustoferri, and R. G. Quivey, Jr., Mol. Microbiol 31:1489-1498, 1999). Here, we report overexpression of the S. mutans apurinic/apyrimidinic (AP) endonuclease, Smx, in Escherichia coli; initial characterization of its enzymatic activity; and analysis of an smx mutant strain of S. mutans. Insertional inactivation of the smx gene eliminates the low-pH-inducible exonuclease activity previously reported. In addition, loss of Smx activity renders the mutant strain sensitive to hydrogen peroxide treatment but relatively unaffected by acid-mediated damage or near-UV irradiation. The smx strain of S. mutans was highly sensitive to the combination of iron and hydrogen peroxide, indicating the likely production of hydroxyl radical by Fenton chemistry with concomitant formation of AP sites that are normally processed by the wild-type allele. Smx activity was sufficiently expressed in E. coli to protect an xth mutant strain from the effects of hydrogen peroxide treatment. The data indicate that S. mutans expresses an inducible, class II-like AP endonuclease, encoded by the smx gene, that exhibits exonucleolytic activity and is regulated as part of the acid-adaptive response of the organism. Smx is likely the primary, if not the sole, AP endonuclease induced during growth at low pH values.

---

* Corresponding author. Mailing address: Center for Oral Biology, Box 611, 601 Elmwood Ave., Rochester, NY 14642. Phone: (585) 275-0382. Fax: (585) 276-0190. E-mail: Robert_Quivey{at}urmc.rochester.edu.

Present address: Roche Molecular Systems, Inc., Branchburg, NJ 08876-1760.

Present address: NIH Clinical Center, Dept. of Laboratory Medicine/Hematology Research, Bethesda, MD 20892.

---

Journal of Bacteriology, April 2005, p. 2705-2714, Vol. 187, No. 8
0021-9193/05/$08.00+0     doi:10.1128/JB.187.8.2705-2714.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Lemos, J. A., Burne, R. A. (2008). A model of efficiency: stress tolerance by Streptococcus mutans. Microbiology 154: 3247-3255 [Abstract] [Full Text]