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Regulation of type 1 fimbriae synthesis and biofilm formation by the transcriptional regulator LrhA of Escherichia coli

Caroline Blumer^1,

¹ Institut für Mikrobiologie und Weinforschung, Johannes Gutenberg Universität Mainz, Becherweg 15, 55099 Mainz, Germany
² Institut für Molekulare Infektionsbiologie der Universität Würzburg, 97070 Würzburg, Germany
³ Institute of Medical Microbiology and Immunology, University of Pécs, 7624 Pécs, Hungary
⁴ Forschungszentrum Jülich, Institut für Biotechnologie I, 52425 Jülich, Germany
⁵ Institut für Mikrobiologie, Universität Regensburg, 93040 Regensburg, Germany

Correspondence
Gottfried Unden
unden{at}uni-mainz.de

Type 1 fimbriae of Escherichia coli facilitate attachment to the host mucosa and promote biofilm formation on abiotic surfaces. The transcriptional regulator LrhA, which is known as a repressor of flagellar, motility and chemotaxis genes, regulates biofilm formation and expression of type 1 fimbriae. Whole-genome expression profiling revealed that inactivation of lrhA results in an increased expression of structural components of type 1 fimbriae. In vitro, LrhA bound to the promoter regions of the two fim recombinases (FimB and FimE) that catalyse the inversion of the fimA promoter, and to the invertible element itself. Translational lacZ fusions with these genes and quantification of fimE transcript levels by real-time PCR showed that LrhA influences type 1 fimbrial phase variation, primarily via activation of FimE, which is required for the ON-to-OFF transition of the fim switch. Enhanced type 1 fimbrial expression as a result of lrhA disruption was confirmed by mannose-sensitive agglutination of yeast cells. Biofilm formation was stimulated by lrhA inactivation and completely suppressed upon LrhA overproduction. The effects of LrhA on biofilm formation were exerted via the changed levels of surface molecules, most probably both flagella and type 1 fimbriae. Together, the data show a role for LrhA as a repressor of type 1 fimbrial expression, and thus as a regulator of the initial stages of biofilm development and, presumably, bacterial adherence to epithelial host cells also.

Present address: Miltenyi Biotec GmbH, 51429 Bergisch-Gladbach, Germany.

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