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Infection and Immunity, April 2003, p. 1972-1979, Vol. 71, No. 4
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.4.1972-1979.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Mutation of luxS Affects Biofilm Formation in Streptococcus mutans

Justin Merritt,1 Fengxia Qi,1 Steven D. Goodman,2 Maxwell H. Anderson,3 and Wenyuan Shi1*

UCLA Molecular Biology Institute and School of Dentistry, Los Angeles, California 90095,1 Department of Diagnostic Sciences, University of Southern California, Los Angeles, California 90089,2 and Washington Dental Service, Seattle, Washington 981253

Received 20 August 2002/ Returned for modification 30 October 2002/ Accepted 18 December 2002

Quorum sensing is a bacterial mechanism for regulating gene expression in response to changes in population density. Many bacteria are capable of acyl-homoserine lactone-based or peptide-based intraspecies quorum sensing and luxS-dependent interspecies quorum sensing. While there is good evidence about the involvement of intraspecies quorum sensing in bacterial biofilm, little is known about the role of luxS in biofilm formation. In this study, we report for the first time that luxS-dependent quorum sensing is involved in biofilm formation of Streptococcus mutans. S. mutans is a major cariogenic bacterium in the multispecies bacterial biofilm commonly known as dental plaque. An ortholog of luxS for S. mutans was identified using the data available in the S. mutans genome project (http://www.genome.ou.edu/smutans.html). Using an assay developed for the detection of the LuxS-associated quorum sensing signal autoinducer 2 (AI-2), it was demonstrated that this ortholog was able to complement the luxS negative phenotype of Escherichia coli DH5{alpha}. It was also shown that AI-2 is indeed produced by S. mutans. AI-2 production is maximal during mid- to late-log growth in batch culture. Mutant strains devoid of the luxS gene were constructed and found to be defective in producing the AI-2 signal. There are also marked phenotypic differences between the wild type and the luxS mutants. Microscopic analysis of in vitro-grown biofilm structure revealed that the luxS mutant biofilms adopted a much more granular appearance, rather than the relatively smooth, confluent layer normally seen in the wild type. These results suggest that LuxS-dependent signal may play an important role in biofilm formation of S. mutans.

* Corresponding author. Mailing address: UCLA School of Dentistry, 10833 Le Conte Ave., Los Angeles, CA 90095-1668. Phone: (310) 825-8356. Fax: (310) 794-7109. E-mail: wenyuan{at}ucla.edu.

Editor: A. D. O'Brien

Infection and Immunity, April 2003, p. 1972-1979, Vol. 71, No. 4
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.4.1972-1979.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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