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Journal of Bacteriology, July 2000, p. 3740-3747, Vol. 182, No. 13
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Role of the dpr Product in Oxygen Tolerance in Streptococcus mutans

Yuji Yamamoto,1 Masako Higuchi,1 Leslie B. Poole,2 and Yoshiyuki Kamio1,*

Laboratory of Applied Microbiology, Department of Molecular and Cell Biology, Graduate School of Agricultural Science, Tohoku University, Amamiya-machi, Aoba-ku, Sendai 981-8555, Japan,1 and Department of Biochemistry, Wake Forest University Medical School, Winston-Salem, North Carolina 271572

Received 15 February 2000/Accepted 20 April 2000

We have previously identified and characterized the alkyl hydroperoxide reductase of Streptococcus mutans, which consists of two components, Nox-1 and AhpC. Deletion of both nox-1 and ahpC had no effect on the sensitivity of S. mutans to cumene hydroperoxide or H2O2, implying that the existence of another antioxidant system(s) independent of the Nox-1-AhpC system compensates for the deficiency. Here, a new antioxidant gene (dpr for Dps-like peroxide resistance gene) was isolated from the S. mutans chromosome by its ability to complement an ahpCF deletion mutant of Escherichia coli with a tert-butyl hydroperoxide-hypersensitive phenotype. The dpr gene complemented the defect in peroxidase activity caused by the deletion of nox-1 and ahpC in S. mutans. Under aerobic conditions, the dpr disruption mutant carrying a spectinomycin resistance gene (dpr::Spcr mutant) grew as well as wild-type S. mutans in liquid medium. However, the dpr::Spcr mutant could not form colonies on an agar plate under air. In addition, neither the dpr::Spcr ahpC::Emr::nox-1 triple mutant nor the dpr::Spcr sod::Emr double mutant was able to grow aerobically in liquid medium. The 20-kDa dpr gene product Dpr is an iron-binding protein. Synthesis of Dpr was induced by exposure of S. mutans cells to air. We propose a mechanism by which Dpr confers aerotolerance on S. mutans.

* Corresponding author. Mailing address: Laboratory of Applied Microbiology, Department of Molecular and Cell Biology, Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumi-dori, Amamiya-machi, Aoba-ku, Sendai 981-8555, Japan. Phone: 81-22-717-8779. Fax: 81-22-717-8780. E-mail: ykamio{at}biochem.tohoku.ac.jp.

Journal of Bacteriology, July 2000, p. 3740-3747, Vol. 182, No. 13
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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