Confirmation of Occurrence of Hydroxamate Siderophores in Soil by a Novel Escherichia coli Bioassay

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Abstract
The occurrence of ferrichrome-type hydroxamate siderophores in soil was confirmed. In the presence of the iron-scavenging chelator ethylenediamine[di( o -hydroxyphenylacetic)acid], soil extract stimulated the growth of an Escherichia coli strain possessing the ferrichrome transport protein (TonA) but did not stimulate growth of a strain lacking this protein (TonA − ). The siderophore concentration in a 1:1 (soil-water) extract was estimated to be approximately 78 nM. Specificity of the assay was supported by the absence of significant differential strain responses to ferric citrate, ferric 2,3-dihydroxybenzoate, enterochelin, ferrioxamine B, coprogen, and triacetylfusigen.