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Microbiology 154 (2008), 431-439; DOI  10.1099/mic.0.2007/011577-0
© 2008 Society for General Microbiology

Regulation of Pseudomonas aeruginosa ptxR by Vfr

Evan Ferrell1, Nancy L. Carty2, Jane A. Colmer-Hamood2, Abdul N. Hamood2 and Susan E. H. West1

1 Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI 53706, USA
2 Department of Microbiology and Immunology, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA

Correspondence
Susan E. H. West
wests{at}vetmed.wisc.edu

Pseudomonas aeruginosa PtxR enhances the expression of the exotoxin A gene toxA. The expression of ptxR itself, which occurs from two promoters (P1 and P2), is not completely understood. We have recently demonstrated that the ptxR upstream region contains potential binding sites for multiple regulators, including the virulence factor regulator Vfr. In this study, we identified within the ptxR upstream region, a 25 bp sequence to which Vfr specifically binds. The sequence is located 20–44 (32.5) bp 5' of the ptxR P2 promoter, and overlaps a potential binding site for the iron-starvation sigma factor PvdS. We also show that, throughout the growth cycle, deletion of vfr reduces ptxR expression from the P2 promoter in the P. aeruginosa strain PAO1 by four- to eightfold, but does not affect ptxR expression from P1. Further, loss of Vfr eliminates the PtxR-induced enhancement in the synthesis of exotoxin A and the metalloproteinase LasB. Our results suggest that Vfr modulates toxA and lasB expression in PAO1 through PtxR. A model defining the relationships between these different genes is presented.

Abbreviations: CRP, cAMP receptor protein; EMSA, electrophoretic mobility shift assay; ETA, exotoxin A; PQS, Pseudomonas quinolone signal; r-Vfr, recombinant Vfr; QS, quorum sensing; Vfr-BS, Vfr-binding sequence






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