SUMMARY: A catechol-type siderophore was secreted by in the growth medium when the cells became iron-deficient. The siderophore, which we call spirilobactin, was purified and a partial characterization of its structure by hydrolysis revealed that it contained 2,3-dihydroxybenzoic acid, ornithine and serine in equimolar amounts. A high-affinity iron transport system capable of Fe uptake from a Fe(III)-spirilobactin complex was also induced in grown under iron deficiency. Kinetic studies on the iron uptake system revealed that it was carrier-mediated, with and values of 0·23 μm and 0·27 nmol Fe min(mg cell protein), respectively. Dependence of iron uptake on an energized membrane, its insensitivity to arsenate and inhibition by protonophores suggest that transport is driven by the proton gradient across the membrane. Iron-deficient transported Fe from the Fe(III)-spirilobactin complex (at a rate 3-fold lower than that of ) but failed to show uptake of iron under the same conditions.


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