title: Autoinducer 2 is required for biofilm growth of Aggregatibacter (Actinobacillus) actinomycetemcomitans.
abstract: 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.
authors.affiliation: Department of Periodontics, Endodontics, and Dental Hygiene, University of Louisville School of Dentistry, 501 South Preston Street, Room 209, Louisville, KY 40292, USA.
authors.forename: Hanjuan
authors.initials: H
authors.lastname: Shao
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lamont
authors.forename: Donald R
authors.initials: DR
authors.lastname: Demuth
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D001422:Bacterial Adhesion / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D018441:Biofilms / Q000254:growth & development*; D013437:Carbon-Sulfur Lyases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D006714:Homoserine / Q000031:analogs & derivatives* / Q000502:physiology; D006801:Humans; D007783:Lactones; D009154:Mutation; D012463:Saliva / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D007783:Lactones; C091088:N-octanoylhomoserine lactone; D006714:Homoserine; D013437:Carbon-Sulfur Lyases; C117753:LuxS protein, Bacteria