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Journal of Bacteriology, November 2008, p. 7500-7507, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.01062-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Alr0397 Is an Outer Membrane Transporter for the Siderophore Schizokinen in Anabaena sp. Strain PCC 7120{triangledown}

Kerstin Nicolaisen,1,{dagger} Suncana Moslavac,2,{dagger} Anastazia Samborski,2 Marianne Valdebenito,3 Klaus Hantke,3 Iris Maldener,3 Alicia M. Muro-Pastor,4 Enrique Flores,4 and Enrico Schleiff1,2*

JWGU Frankfurt am Main, CEF-Macromolecular Complexes, Center of Membrane Proteomics, Department of Biosciences, Max-von-Laue Str. 9, 60439 Frankfurt, Germany,1 LMU, Department of Biology I, Menzinger Str. 67, 80638 Munich, Germany,2 Department of Microbiology/Organismic Interactions, Faculty of Biology, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany,3 Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC and Universidad de Sevilla, Avda. Américo Vespucio 49, E-41092 Seville, Spain4

Received 30 July 2008/ Accepted 8 September 2008

Iron uptake in proteobacteria by TonB-dependent outer membrane transporters represents a well-explored subject. In contrast, the same process has been scarcely investigated in cyanobacteria. The heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 is known to secrete the siderophore schizokinen, but its transport system has remained unidentified. Inspection of the genome of strain PCC 7120 shows that only one gene encoding a putative TonB-dependent iron transporter, namely alr0397, is positioned close to genes encoding enzymes involved in the biosynthesis of a hydroxamate siderophore. The expression of alr0397, which encodes an outer membrane protein, was elevated under iron-limited conditions. Inactivation of this gene caused a moderate phenotype of iron starvation in the mutant cells. The characterization of the mutant strain showed that Alr0397 is a TonB-dependent schizokinen transporter (SchT) of the outer membrane and that alr0397 expression and schizokinen production are regulated by the iron homeostasis of the cell.

* Corresponding author. Mailing address: Molecular Cell Biology of Plants, Biocenter, N 200, 3. OG, Max-von-Laue-Str. 9, D-60438 Frankfurt/Main, Germany. Phone: 49-69 798-29285. Fax: 49-69 798-29286. E-mail: schleiff{at}bio.uni-frankfurt.de

{triangledown} Published ahead of print on 19 September 2008.

{dagger} K. Nicolaisen and S. Moslavac contributed equally to this work.

Journal of Bacteriology, November 2008, p. 7500-7507, Vol. 190, No. 22
0021-9193/08/$08.00+0     doi:10.1128/JB.01062-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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