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Journal of Bacteriology, May 2006, p. 3365-3370, Vol. 188, No. 9
0021-9193/06/$08.00+0     doi:10.1128/JB.188.9.3365-3370.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

A Distinct QscR Regulon in the Pseudomonas aeruginosa Quorum-Sensing Circuit{dagger}

Yannick Lequette,1 Joon-Hee Lee,1 Fouzia Ledgham,2 Andrée Lazdunski,2 and E. Peter Greenberg1*

Department of Microbiology, University of Washington, Seattle, Washington 98195,1 Laboratoire d'Ingénierie des Systèmes Macromoléculaires, IBSM/CNRS, Marseille 13402, Cedex 20, France2

Received 12 October 2005/ Accepted 1 February 2006

The opportunistic pathogen Pseudomonas aeruginosa possesses two complete acyl-homoserine lactone (acyl-HSL) signaling systems. One system consists of LasI and LasR, which generate a 3-oxododecanoyl-homoserine lactone signal and respond to that signal, respectively. The other system is RhlI and RhlR, which generate butanoyl-homoserine lactone and respond to butanoyl-homoserine lactone, respectively. These quorum-sensing systems control hundreds of genes. There is also an orphan LasR-RhlR homolog, QscR, for which there is no cognate acyl-HSL synthetic enzyme. We previously reported that a qscR mutant is hypervirulent and showed that QscR transiently represses a few quorum-sensing-controlled genes. To better understand the role of QscR in P. aeruginosa gene regulation and to better understand the relationship between QscR, LasR, and RhlR control of gene expression, we used transcription profiling to identify a QscR-dependent regulon. Our analysis revealed that QscR activates some genes and represses others. Some of the repressed genes are not regulated by the LasR-I or RhlR-I systems, while others are. The LasI-generated 3-oxododecanoyl-homoserine lactone serves as a signal molecule for QscR. Thus, QscR appears to be an integral component of the P. aeruginosa quorum-sensing circuitry. QscR uses the LasI-generated acyl-homoserine lactone signal and controls a specific regulon that overlaps with the already overlapping LasR- and RhlR-dependent regulons.

* Corresponding author. Mailing address: Department of Microbiology, HSB Room G-328, 1959 NE Pacific Street, Seattle, WA 98195-7242. Phone: (206) 616-2881. Fax: (206) 616-2938. E-mail: epgreen{at}u.washington.edu.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, May 2006, p. 3365-3370, Vol. 188, No. 9
0021-9193/06/$08.00+0     doi:10.1128/JB.188.9.3365-3370.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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