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Journal of Bacteriology, November 2000, p. 6401-6411, Vol. 182, No. 22
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The Pseudomonas aeruginosa Lectins PA-IL and PA-IIL Are Controlled by Quorum Sensing and by RpoS

Klaus Winzer,1,2 Colin Falconer,1 Nachman C. Garber,3 Stephen P. Diggle,1 Miguel Camara,1 and Paul Williams1,2,*

School of Pharmaceutical Sciences1 and Institute of Infections and Immunity,2 University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom, and Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 52 900, Israel3

Received 15 May 2000/Accepted 5 September 2000

In Pseudomonas aeruginosa, many exoproduct virulence determinants are regulated via a hierarchical quorum-sensing cascade involving the transcriptional regulators LasR and RhlR and their cognate activators, N-(3-oxododecanoyl)-L-homoserine lactone (3O-C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL). In this paper, we demonstrate that the cytotoxic lectins PA-IL and PA-IIL are regulated via quorum sensing. Using immunoblot analysis, the production of both lectins was found to be directly dependent on the rhl locus while, in a lasR mutant, the onset of lectin synthesis was delayed but not abolished. The PA-IL structural gene, lecA, was cloned and sequenced. Transcript analysis indicated a monocistronic organization with a transcriptional start site 70 bp upstream of the lecA translational start codon. A lux box-type element together with RpoS (sigma S) consensus sequences was identified upstream of the putative promoter region. In Escherichia coli, expression of a lecA::lux reporter fusion was activated by RhlR/C4-HSL, but not by LasR/3O-C12-HSL, confirming direct regulation by RhlR/C4-HSL. Similarly, in P. aeruginosa PAO1, the expression of a chromosomal lecA::lux fusion was enhanced but not advanced by the addition of exogenous C4-HSL but not 3O-C12-HSL. Furthermore, mutation of rpoS abolished lectin synthesis in P. aeruginosa, demonstrating that both RpoS and RhlR/C4-HSL are required. Although the C4-HSL-dependent expression of the lecA::lux reporter in E. coli could be inhibited by the presence of 3O-C12-HSL, this did not occur in P. aeruginosa. This suggests that, in the homologous genetic background, 3O-C12-HSL does not function as a posttranslational regulator of the RhlR/C4-HSL-dependent activation of lecA expression.

* Corresponding author. Mailing address: School of Pharmaceutical Sciences, University Park, University of Nottingham, Nottingham NG7 2RD, United Kingdom. Phone: (44)115 9515047. Fax: (44)115 8466296. E-mail: paul.williams{at}nottingham.ac.uk.

Journal of Bacteriology, November 2000, p. 6401-6411, Vol. 182, No. 22
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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