AEM Accepts, published online ahead of print on 11 January 2008

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Appl. Environ. Microbiol. doi:10.1128/AEM.02236-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Vanadium requirements and uptake kinetics in the dinitrogen-fixing bacterium Azotobacter vinelandii

J. P. Bellenger, T. Wichard, and A. M.L. Kraepiel

Department of Geosciences, Guyot Hall, Princeton University, Princeton NJ 08544, USA.; UMR 7517 (CNRS-ULP), EOST, 1 Rue Blessig, 67084 Strasbourg Cedex, France; Chemistry Department, PEI, Guyot Hall, Princeton University, Princeton NJ 08544, USA

Vanadium (V) is a cofactor in the alternative V-nitrogenase that is expressed by some N₂-fixing bacteria when Mo is not available. We investigated the V requirements, the kinetics of V uptake and the production of catechol compounds over a range of concentrations of vanadium in diazotrophic cultures of the soil bacterium Azotobacter vinelandii. In strain CA11.70, a mutant that expresses only the V nitrogenase, V concentrations in the medium between 10^-8 M and 10^-6 M sustain maximum growth rates; they are limiting below this range and toxic above. A. vinelandii excretes in its growth medium micromolar concentrations of the catechol siderophores azotochelin and protochelin which bind the vanadate oxoanion. The production of catechols increases when V concentrations become toxic. Short term uptake experiments with the radioactive isotope ⁴⁹V show that bacteria take up the V-catechol complexes through a regulated transport system(s) which shuts down at high V concentrations. The modulation of the excretion of catechols and of the uptake of these V complexes allows A. vinelandii to precisely manage its V homeostasis over a range of V concentrations, from limiting to toxic.