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Journal of Bacteriology, February 2009, p. 795-804, Vol. 191, No. 3
0021-9193/09/$08.00+0     doi:10.1128/JB.00845-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Erwinia chrysanthemi Iron Metabolism: the Unexpected Implication of the Inner Membrane Platform within the Type II Secretion System ^,

Vanessa Douet,^1, Dominique Expert,² Frédéric Barras,¹ and Béatrice Py^1*

LCB, CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France,¹ LPV, UMR217, 16 rue Claude Bernard, 75005 Paris, France²

Received 19 June 2008/ Accepted 23 October 2008

The type II secretion (T2S) system is an essential device for Erwinia chrysanthemi virulence. Previously, we reported the key role of the OutF protein in forming, along with OutELM, an inner membrane platform in the Out T2S system. Here, we report that OutF copurified with five proteins identified by matrix-assisted laser desorption ionization-time of flight analysis as AcsD, TogA, SecA, Tsp, and DegP. The AcsD protein was known to be involved in the biosynthesis of achromobactin, which is a siderophore important for E. chrysanthemi virulence. The yeast two-hybrid system allowed us to gain further evidence for the OutF-AcsD interaction. Moreover, we showed that lack of OutF produced a pleiotropic phenotype: (i) altered production of the two siderophores of E. chrysanthemi, achromobactin and chrysobactin; (ii) hypersensitivity to streptonigrin, an iron-activated antibiotic; (iii) increased sensitivity to oxidative stress; and (iv) absence of the FbpA-like iron-binding protein in the periplasmic fraction. Interestingly, outE and outL mutants also exhibited similar phenotypes, but, outD and outJ mutants did not. Moreover, using the yeast two-hybrid system, several interactions were shown to occur between components of the T2S system inner membrane platform (OutEFL) and proteins involved in achromobactin production (AcsABCDE). The OutL-AcsD interaction was also demonstrated by Ni²⁺ affinity chromatography. These results fully confirm our previous view that the T2S machinery is made up of three discrete blocks. The OutEFLM-forming platform is proposed to be instrumental in two different processes essential for virulence, protein secretion and iron homeostasis.

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* Corresponding author. Mailing address: LCB, CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France. Phone: (33) 4 91 16 44 31. Fax: (33) 4 91 71 89 14. E-mail: py{at}ibsm.cnrs-mrs.fr

Published ahead of print on 31 October 2008.

Supplemental material for this article may be found at http://jb.asm.org/.

Present address: Department of Tropical Medicine, Medical Microbiology, and Pharmacology, John A. Burns School of Medicine, University of Hawaii, 1960 East West Road, Honolulu, HI 96822.

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Journal of Bacteriology, February 2009, p. 795-804, Vol. 191, No. 3
0021-9193/09/$08.00+0     doi:10.1128/JB.00845-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

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