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Infection and Immunity, September 2007, p. 4211-4218, Vol. 75, No. 9
0019-9567/07/$08.00+0     doi:10.1128/IAI.00402-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Autoinducer 2 Is Required for Biofilm Growth of Aggregatibacter (Actinobacillus) actinomycetemcomitans{triangledown}

Hanjuan Shao,1 Richard J. Lamont,2 and Donald R. Demuth1*

Department of Periodontics, Endodontics, and Dental Hygiene, University of Louisville School of Dentistry, Louisville, Kentucky,1 Department of Oral Biology, University of Florida School of Dentistry, Gainesville, Florida2

Received 16 March 2007/ Returned for modification 30 April 2007/ Accepted 11 June 2007

Autoinducer 2 (AI-2) is required for the growth of Aggregatibacter (Actinobacillus) actinomycetemcomitans in culture under conditions of iron limitation. However, in vivo this organism thrives in a complex multispecies biofilm that forms in the human oral cavity. In this report, we show that adherent growth of A. actinomycetemcomitans on a saliva-coated surface, but not planktonic growth under iron-replete conditions, is defective in a LuxS-deficient background. Biofilm growth of the luxS mutant exhibited lower total biomass and lower biofilm depth than those for the wild-type strain. Normal biofilm growth of the luxS mutant was restored genetically by introduction of a functional copy of luxS and biochemically by addition of partially purified AI-2. Furthermore, introduction of S-adenosylhomocysteine hydrolase, which restores the metabolism of S-adenosylmethionine in the absence of LuxS, into A. actinomycetemcomitans did not complement the luxS mutation unless AI-2 was added in trans. This suggests that AI-2 itself is required for biofilm growth by A. actinomycetemcomitans. A biofilm growth deficiency similar to that of the LuxS-deficient strain was also observed when a gene encoding the AI-2-interacting protein RbsB or LsrB was inactivated. Biofilm formation by A. actinomycetemcomitans was virtually eliminated upon inactivation of both rbsB and lsrB. In addition, biofilm growth by wild-type A. actinomycetemcomitans was reduced in the presence of ribose, which competes with AI-2 for binding to RbsB. These results suggest that RbsB and LsrB function as AI-2 receptors in A. actinomycetemcomitans and that the development of A. actinomycetemcomitans biofilms requires AI-2.

* Corresponding author. Mailing address: Department of Periodontics, Endodontics, and Dental Hygiene, University of Louisville School of Dentistry, 501 South Preston Street, Room 209, Louisville, KY 40292. Phone: (502) 852-3807. Fax: (502) 852-4052. E-mail: drdemu01{at}louisville.edu

{triangledown} Published ahead of print on 25 June 2007.

Editor: F. C. Fang

Infection and Immunity, September 2007, p. 4211-4218, Vol. 75, No. 9
0019-9567/07/$08.00+0     doi:10.1128/IAI.00402-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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