title: An efflux pump is required for siderophore recycling by Pseudomonas aeruginosa.
abstract: Pyoverdine (PVDI) is a siderophore produced by Pseudomonas aeruginosa in order to obtain iron. This molecule is composed of a fluorescent chromophore linked to an octapeptide. Following secretion from the bacteria, PVDI chelates iron ions and the resulting Fe-PVDI complexes are taken up by the bacteria through a cell surface receptor protein. The iron is released in the periplasm and the resulting PVDI is recycled, being secreted out of the bacteria by a previously unknown mechanism. Three genes with the potential to encode an efflux system are adjacent to, and coregulated with, genes required for PVDI-mediated iron transport. Mutation of genes encoding this efflux pump (named PvdRT-OpmQ) prevented recycling of PVDI from the periplasm into the extracellular medium. Fluorescence microscopy showed that in the mutant bacteria PVDI accumulated in the periplasm. Gallium (Ga(3+) ), a metal that cannot be removed from PVDI by reduction, is taken up by P. aeruginosa when chelated by PVDI. Recycling did not occur after transport of PVDI-Ga(3+) and fluorescence accumulated in the periplasm even when the PvdRT-OpmQ efflux pump was functional. Cellular fractionation showed that PVDI-synthesizing bacteria lacking PvdRT-OpmQ secreted PVDI but had an approximately 20-fold increase in the amount of PVD present in the periplasm, consistent with an inability to recycle PVDI. Collectively, these data show that PvdRT-OpmQ is involved in recycling of PVDI from the periplasm to the extracellular medium and recycling requires release of the metal ion from PVDI.
authors.affiliation: Metaux et microorganismes: Chimie, Biologie et Applications. FRE 3211, CNRS-Université de Strasbourg, ESBS, Blvd Sébastien Brant, F-67413 Illkirch, Strasbourg, France. Department of Biochemistry, University of Otago, PO Box 56, Dunedin, New Zealand.
authors.forename: Emilie
authors.initials: E
authors.lastname: Yeterian
authors.forename: Lois W
authors.initials: LW
authors.lastname: Martin
authors.forename: Iain L
authors.initials: IL
authors.lastname: Lamont
authors.forename: Isabelle J
authors.initials: IJ
authors.lastname: Schalk