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Infection and Immunity, June 2004, p. 3489-3494, Vol. 72, No. 6
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.6.3489-3494.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Identification of a Novel Two-Component System in Streptococcus gordonii V288 Involved in Biofilm Formation

Yongshu Zhang,1 Yu Lei,1 Ali Khammanivong,1 and Mark C. Herzberg1,2*

Department of Oral Sciences, School of Dentistry,1 Mucosal and Vaccine Research Center, University of Minnesota, Minneapolis, Minnesota 554552

Received 30 September 2003/ Returned for modification 31 October 2003/ Accepted 13 February 2004

Streptococcus gordonii is a pioneer colonizer of the teeth, contributing to the initiation of the oral biofilm called dental plaque. To identify genes that may be important in biofilm formation, a plasmid integration library of S. gordonii V288 was used. After screening for in vitro biofilm formation on polystyrene, a putative biofilm-defective mutant was isolated. In this mutant, pAK36 was inserted into a locus encoding a novel two-component system (bfr [biofilm formation related]) with two cotranscribed genes that form an operon. bfrA encodes a putative response regulator, while bfrB encodes a receptor histidine kinase. The bfr mutant and wild-type strain V288 showed similar growth rates in Todd-Hewitt broth (THB). A bfr-cat fusion strain was constructed. During growth in THB, the reporter activity (chloramphenicol acetyltransferase) was first detected in mid-log phase and reached a maximum in stationary phase, suggesting that transcription of bfr was growth stage dependent. After being harvested from THB, the bfr mutant adhered less effectively than did wild-type strain V288 to saliva-coated hydroxyapatite (sHA). To simulate pioneer colonization of teeth, S. gordonii V288 was incubated with sHA for 4 h in THB with 10% saliva to develop biofilms. RNA was isolated, and expression of bfrAB was estimated. In comparison to that of cells grown in suspension (free-growing cells), bfr mRNA expression by sessile cells on sHA was 1.8-fold greater and that by surrounding planktonic cells was 3.5-fold greater. Therefore, bfrAB is a novel two-component system regulated in association with S. gordonii biofilm formation in vitro.


* Corresponding author. Mailing address: Department of Oral Sciences and Mucosal and Vaccine Research Center, University of Minnesota, 17-164 Moos Tower, 515 Delaware St., SE, Minneapolis, MN 55455. Phone: (612) 625-8404. Fax: (612) 626-2651. E-mail: mcherzb{at}umn.edu.

Editor: J. B. Bliska


Infection and Immunity, June 2004, p. 3489-3494, Vol. 72, No. 6
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.6.3489-3494.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.




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