An efflux pump is required for siderophore recycling by Pseudomonas aeruginosa

Authors

  • Emilie Yeterian,

    1. Metaux et microorganismes: Chimie, Biologie et Applications. FRE 3211, CNRS-Université de Strasbourg, ESBS, Blvd Sébastien Brant, F-67413 Illkirch, Strasbourg, France.
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  • Lois W. Martin,

    1. Department of Biochemistry, University of Otago, PO Box 56, Dunedin, New Zealand.
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  • Iain L. Lamont,

    Corresponding author
    1. Department of Biochemistry, University of Otago, PO Box 56, Dunedin, New Zealand.
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  • Isabelle J. Schalk

    Corresponding author
    1. Metaux et microorganismes: Chimie, Biologie et Applications. FRE 3211, CNRS-Université de Strasbourg, ESBS, Blvd Sébastien Brant, F-67413 Illkirch, Strasbourg, France.
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E-mail iain.lamont@otago.ac.nz; Tel. (+64) 3479 7869; Fax (+64) 3479 7866;

E-mail isabelle.schalk@unistra.fr; Tel. (+33) 3 90 24 47 19; Fax (+33) 3 90 24 48 29.

Summary

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 (Ga3+), 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–Ga3+ 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.

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