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Journal of Bacteriology, October 2003, p. 5967-5975, Vol. 185, No. 20
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.20.5967-5975.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

The sloABCR Operon of Streptococcus mutans Encodes an Mn and Fe Transport System Required for Endocarditis Virulence and Its Mn-Dependent Repressor

Sehmi Paik,1,2 Arunsri Brown,1 Cindy L. Munro,3 Cynthia Nau Cornelissen,2 and Todd Kitten1,2*

The Philips Institute of Oral and Craniofacial Molecular Biology,1 Department of Microbiology and Immunology,2 Department of Adult Health Nursing, Virginia Commonwealth University, Richmond, Virginia 232983

Received 14 July 2003/ Accepted 29 July 2003

Streptococcus mutans belongs to the viridans group of oral streptococci, which is the leading cause of endocarditis in humans. The LraI family of lipoproteins in viridans group streptococci and other bacteria have been shown to function as virulence factors, adhesins, or ABC-type metal transporters. We previously reported the identification of the S. mutans LraI operon, sloABCR, which encodes components of a putative metal uptake system composed of SloA, an ATP-binding protein, SloB, an integral membrane protein, and SloC, a solute-binding lipoprotein, as well as a metal-dependent regulator, SloR. We report here the functional analysis of this operon. By Western blotting, addition of Mn to the growth medium repressed SloC expression in a wild-type strain but not in a sloR mutant. Other metals tested had little effect. Cells were also tested for aerobic growth in media stripped of metals then reconstituted with Mg and either Mn or Fe. Fe at 10 µM supported growth of the wild-type strain but not of a sloA or sloC mutant. Mn at 0.1 µM supported growth of the wild-type strain and sloR mutant but not of sloA or sloC mutants. The combined results suggest that the SloABC proteins transport both metals, although the SloR protein represses this system only in response to Mn. These conclusions are supported by 55Fe uptake studies with Mn as a competitor. Finally, a sloA mutant demonstrated loss of virulence in a rat model of endocarditis, suggesting that metal transport is required for endocarditis pathogenesis.

* Corresponding author. Mailing address: The Philips Institute of Oral and Craniofacial Molecular Biology, 521 North 11th St., Box 980566, Virginia Commonwealth University, Richmond, VA 23298-0566. Phone: (804) 628-7010. Fax: (804) 828-0150. E-mail: tkitten{at}vcu.edu.

Journal of Bacteriology, October 2003, p. 5967-5975, Vol. 185, No. 20
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.20.5967-5975.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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