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Infection and Immunity, June 2000, p. 3193-3199, Vol. 68, No. 6
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Intercellular Communication in Helicobacter pylori: luxS Is Essential for the Production of an Extracellular Signaling Molecule

Mark H. Forsyth1 and Timothy L. Cover1,2,*

Departments of Medicine and Microbiology and Immunology, Vanderbilt University School of Medicine,1 and Veterans Affairs Medical Center,2 Nashville, Tennessee

Received 13 December 1999/Returned for modification 10 February 2000/Accepted 24 February 2000

Individual bacteria of numerous species can communicate and coordinate their actions via the production, release, and detection of extracellular signaling molecules. In this study, we used the Vibrio harveyi luminescence bioassay to determine whether Helicobacter pylori produces such a factor. Cell-free conditioned media from H. pylori strains 60190 and 26695 each induced >100-fold-greater luminescence in V. harveyi than did sterile culture medium. The H. pylori signaling molecule had a molecular mass of <10 kDa, and its activity was unaffected by heating to 80°C for 5 min or protease treatment. The genome sequence of H. pylori 26695 does not contain any gene predicted to encode an acyl homoserine lactone synthase but does contain an orthologue of luxS, which is required for production of autoinducer-2 (AI-2) in V. harveyi. To evaluate the role of luxS in H. pylori, we constructed luxS null mutants derived from H. pylori 60190 and 26695. Conditioned media from the wild-type H. pylori strains induced >100-fold-greater luminescence in the V. harveyi bioassay than did conditioned medium from either mutant strain. Production of the signaling molecule was restored in an H. pylori luxS null mutant strain by complementation with a single intact copy of luxS placed in a heterologous site on the chromosome. In addition, Escherichia coli DH5alpha produced autoinducer activity following the introduction of an intact copy of luxS from H. pylori. Production of the signaling molecule by H. pylori was growth phase dependent, with maximal production occurring in the mid-exponential phase of growth. Transcription of H. pylori vacA also was growth phase dependent, but this phenomenon was not dependent on luxS activity. These data indicate that H. pylori produces an extracellular signaling molecule related to AI-2 from V. harveyi. We speculate that this signaling molecule may play a role in regulating H. pylori gene expression.

* Corresponding author. Mailing address: Division of Infectious Diseases, Medical Center North A3310, Vanderbilt University School of Medicine, Nashville, TN 37232-2605. Phone: (615) 322-2035. Fax: (615) 343-6160. E-mail: covertl{at}ctrvax.vanderbilt.edu.

Infection and Immunity, June 2000, p. 3193-3199, Vol. 68, No. 6
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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