Siderophore-mediated iron uptake in different strains of Anabaena sp

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Abstract
Anabaena sp. strain 6411, which produces the dihydroxamate siderophore schizokinen to facilitate Fe uptake, is also capable of using the related siderophore aerobactin. The 2 siderophores compete for the same Fe transport system, but there is a markedly higher affinity for ferric schizokinen than for ferric aerobactin. The trihydroxyamate siderophore ferrioxamine B is far less effective as an Fe donor in this organism. Anabaena sp. strain 7120 appears to be closely related to strain 6411. It synthesizes schizokinen as its major siderophore and shows rates of Fe uptake from ferric schizokinen, ferric aerobactin and ferrioxamine B which are similar to those observed with strain 6411. Anabaena cylindrica Lemm. 7122 and 1611 differ from strain 6411. In contrast to schizokinen, the hydroxamate which they produce in response to Fe starvation cannot be extracted with water from the organic layer and does not support the growth of the siderophore auxotroph Arthrobacter flavescens JG-9. Strain 7122 can use its endogenous siderophore or schizokinen to promote Fe uptake, but at 50-fold-lower rates than are observed with Anabaena sp. strain 6411 or 7120.