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J Bacteriol, May 1998, p. 2442-2449, Vol. 180, No. 9
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Isolation of an Escherichia coli K-12 Mutant Strain Able To Form Biofilms on Inert Surfaces: Involvement of a New ompR Allele That Increases Curli Expression

Olivier Vidal,1 Robert Longin,2 Claire Prigent-Combaret,1 Corinne Dorel,1 Michel Hooreman,3 and Philippe Lejeune1,*

Laboratoire de Génétique Moléculaire des Microorganismes et des Interactions Cellulaires, CNRS UMR 5577, Institut National des Sciences Appliquées de Lyon, 69621 Villeurbanne,1 Laboratoire des Fermentations, Unité de Physiologie Cellulaire, Département des Biotechnologies, Institut Pasteur, 75724 Paris Cedex 15,2 and Panstimase SARL, 75009 Paris,3 France

Received 9 October 1997/Accepted 27 February 1998

Classical laboratory strains of Escherichia coli do not spontaneously colonize inert surfaces. However, when maintained in continuous culture for evolution studies or industrial processes, these strains usually generate adherent mutants which form a thick biofilm, visible with the naked eye, on the wall of the culture apparatus. Such a mutant was isolated to identify the genes and morphological structures involved in biofilm formation in the very well characterized E. coli K-12 context. This mutant acquired the ability to colonize hydrophilic (glass) and hydrophobic (polystyrene) surfaces and to form aggregation clumps. A single point mutation, resulting in the replacement of a leucine by an arginine residue at position 43 in the regulatory protein OmpR, was responsible for this phenotype. Observations by electron microscopy revealed the presence at the surfaces of the mutant bacteria of fibrillar structures looking like the particular fimbriae described by the Olsén group and designated curli (A. Olsén, A. Jonsson, and S. Normark, Nature 338:652-655, 1989). The production of curli (visualized by Congo red binding) and the expression of the csgA gene encoding curlin synthesis (monitored by coupling a reporter gene to its promoter) were significantly increased in the presence of the ompR allele described in this work. Transduction of knockout mutations in either csgA or ompR caused the loss of the adherence properties of several biofilm-forming E. coli strains, including all those which were isolated in this work from the wall of a continuous culture apparatus and two clinical strains isolated from patients with catheter-related infections. These results indicate that curli are morphological structures of major importance for inert surface colonization and biofilm formation and demonstrate that their synthesis is under the control of the EnvZ-OmpR two-component regulatory system.

* Corresponding author. Mailing address: Laboratoire de Génétique Moléculaire des Microorganismes, INSA de Lyon, 20 avenue Albert Einstein, 69621 Villeurbanne, France. Phone: (33) 4 72 43 87 06. Fax: (33) 4 72 43 87 14. E-mail: lejeune{at}insa.insa-lyon.fr.

J Bacteriol, May 1998, p. 2442-2449, Vol. 180, No. 9
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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Copyright © 1998 by the American Society for Microbiology. All rights reserved.