Pseudomonas aeruginosa is an important opportunistic pathogen, and one of the major factors contributing to its virulence is the capacity to produce a high-affinity iron-scavenging siderophore, pyoverdine (10, 11, 21). Pyover-dines form a family of peptidic siderophores comprising a variable peptide chain and a chromophore conferring the characteristic fluorescence of the apo-pyoverdine (11, 15, 21). Pyoverdines not only are siderophores but also can be considered to be authentic signal molecules, since the interaction of ferripyoverdine with the FpvA receptor triggers a signaling cascade for the production of virulence factors such as exotoxin A and the protease PrpL (9, 20, 21). Furthermore, the pyoverdine-mediated iron uptake system is importantfor the formation of biofilms by P. aeruginosa (1, 8). The FpvA receptor has been copurified with pyoverdine and its three-dimensional structure determined, confirming its association with what was then thought to be apo-pyoverdine because of its strongfluorescence (3, 1). In this issue, Greenwald et al. show that this molecule associated with FpvA is not apo-pyoverdine but Al-pyoverdine (6). As we will see, this discovery changes the way ferripyoverdine uptake is considered to occur (Fig. 1).
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Microbial Interactions, Department of Molecular and Cellular Interactions, Flanders Institute for Biotechnology (VIE) and Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium;
