| 11021919 |
Baysse C, De Vos D, Naudet Y, Vandermonde A, Ochsner U, Meyer JM, Budzikiewicz H, Schafer M, Fuchs R, Cornelis P: Vanadium interferes with siderophore-mediated iron uptake in Pseudomonas aeruginosa. Microbiology. 2000 Oct;146 ( Pt 10):2425-34.
Vanadium is a metal that under physiological conditions can exist in two oxidation states, V (IV) (vanadyl ion) and V (V) (vanadate ion). Here, it was demonstrated that both ions can form complexes with siderophores. Pseudomonas aeruginosa produces two siderophores under iron-limiting conditions, pyoverdine (PVD) and pyochelin (PCH). Vanadyl sulfate, at a concentration of 1-2 mM, strongly inhibited growth of P. aeruginosa PAO1, especially under conditions of severe iron limitation imposed by the presence of non-utilizable Fe (III) chelators. PVD-deficient mutants were more sensitive to vanadium than the wild-type, but addition of PVD did not stimulate their growth. Conversely, PCH-negative mutants were more resistant to vanadium than the wild-type strain. Both siderophores could bind and form complexes with vanadium after incubation with vanadyl sulfate (1:1, in the case of PVD; 2:1, in the case of PCH). Although only one complex with PVD, V (IV)-PVD, was found, both V (IV)- and V (V)-PCH were detected. V-PCH, but not V-PVD, caused strong growth reduction, resulting in a prolonged lag phase. Exposure of PAO1 cells to vanadium induced resistance to the superoxide-generating compound paraquat, and conversely, exposure to paraquat increased resistance to V (IV). Superoxide dismutase (SOD) activity of cells grown in the presence of V (IV) was augmented by a factor of two. Mutants deficient in the production of Fe-SOD (SodB) were particularly sensitive to vanadium, whilst sodA mutants deficient for Mn-SOD were only marginally affected. In conclusion, it is suggested that V-PCH catalyses a Fenton-type reaction whereby the toxic superoxide anion O (2)- is generated, and that vanadium compromises PVD utilization. |
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