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Applied and Environmental Microbiology, April 2001, p. 1865-1873, Vol. 67, No. 4
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.4.1865-1873.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Quorum-Sensing Genes in Pseudomonas aeruginosa Biofilms: Their Role and Expression Patterns

Teresa R. De Kievit,1 Richard Gillis,1 Steve Marx,2 Chris Brown,2 and Barbara H. Iglewski1,*

Department of Microbiology and Immunology1 and Department of Computer Science,2 University of Rochester Medical Center, Rochester, New York 14642

Received 2 October 2000/Accepted 12 January 2001

Acylated homoserine lactone molecules are used by a number of gram-negative bacteria to regulate cell density-dependent gene expression by a mechanism known as quorum sensing (QS). In Pseudomonas aeruginosa, QS or cell-to-cell signaling controls expression of a number of virulence factors, as well as biofilm differentiation. In this study, we investigated the role played by the las and rhl QS systems during the early stages of static biofilm formation when cells are adhering to a surface and forming microcolonies. These studies revealed a marked difference in biofilm formation between the PAO1 parent and the QS mutants when glucose, but not citrate, was used as the sole carbon source. To further elucidate the contribution of lasI and rhlI to biofilm maturation, we utilized fusions to unstable green fluorescent protein in concert with confocal microscopy to perform real-time temporal and spatial studies of these genes in a flowing environment. During the course of 8-day biofilm development, lasI expression was found to progressively decrease over time. Conversely, rhlI expression remained steady throughout biofilm development but occurred in a lower percentage of cells. Spatial analysis revealed that lasI and rhlI were maximally expressed in cells located at the substratum and that expression decreased with increasing biofilm height. Because QS was shown previously to be involved in biofilm differentiation, these findings have important implications for the design of biofilm prevention and eradication strategies.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, University of Rochester, 601 Elmwood Ave., Box 672, Rochester, NY 14642. Phone: (716) 275-3402. Fax: (716) 473-9573. E-mail: bigl{at}uhura.cc.rochester.edu.

Applied and Environmental Microbiology, April 2001, p. 1865-1873, Vol. 67, No. 4
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.4.1865-1873.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.