Dihydroxybenzoylserine, the breakdown product of enterochelin, was able to stimulate growth of Escherichia coli under iron limiting conditions by acting as a siderophore. The dihydroxybenzoylserine-iron complex was taken up via the outer membrane receptor proteins Fiu, FepA and to a minor extent via Cir. Transport of Fe3(+)-dihydroxybenzoylserine across the cytoplasmic membrane was only dependent on genes from the fep region. In addition, it was shown that dihydroxybenzoate was taken up via Fiu and Cir and less efficiently by FepA.