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Journal of Bacteriology, March 2006, p. 1882-1891, Vol. 188, No. 5
0021-9193/06/$08.00+0 doi:10.1128/JB.188.5.1882-1891.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Department of Medical Microbiology, VU Medical Center, 1081 BT Amsterdam,1 Department of Molecular and Cellular Neurobiology and Proteomics Center VU (Medical Center), 1081 HV Amsterdam, The Netherlands2
Received 10 November 2005/ Accepted 12 December 2005
Pseudomonas aeruginosa secretes two siderophores, pyoverdine and pyochelin, under iron-limiting conditions. These siderophores are recognized at the cell surface by specific outer membrane receptors, also known as TonB-dependent receptors. In addition, this bacterium is also able to incorporate many heterologous siderophores of bacterial or fungal origin, which is reflected by the presence of 32 additional genes encoding putative TonB-dependent receptors. In this work, we have used a proteomic approach to identify the inducing conditions for P. aeruginosa TonB-dependent receptors. In total, 11 of these receptors could be discerned under various conditions. Two of them are only produced in the presence of the hydroxamate siderophores ferrioxamine B and ferrichrome. Regulation of their synthesis is affected by both iron and the presence of a cognate siderophore. Analysis of the P. aeruginosa genome showed that both receptor genes are located next to a regulatory locus encoding an extracytoplasmic function sigma factor and a transmembrane sensor. The involvement of this putative regulatory locus in the specific induction of the ferrioxamine B and ferrichrome receptors has been demonstrated. These results show that P. aeruginosa has evolved multiple specific regulatory systems to allow the regulation of TonB-dependent receptors.
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