SIDEROPHORE-MEDIATED IRON UPTAKE IN ALCALIGENES-EUTROPHUS CH34 AND IDENTIFICATION OF ALEB ENCODING THE FERRIC IRON-ALCALIGIN-E RECEPTOR

Siderophore production in response to iron limitation was observed in Alcaligenes eutrophus CH34, and the corresponding siderophore was name d alcaligin E. Alcaligin E was characterized as a phenolate-type sider ophore containing neither catecholate nor hydroxamate groups, Alcaligi n E promoted the growth of siderophore-deficient A. eutrophus mutants under iron-restricted conditions and promoted Fe-59 uptake by iron-lim ited cells. However, the growth of the Sid(-) mutant AE1152, which was obtained from CH34 by Tn5-Tc mutagenesis, was completely inhibited by the addition of alcaligin E, AE1152 also showed strongly reduced (59) Pe uptake in the presence of alcaligin E, This indicates that a gene, designated aleB, which is involved in transport of ferric iron-alcalig in E across the membrane is inactivated, The aleB gene was cloned, and its putative amino acid sequence showed strong similarity to those of ferric iron-siderophore receptor proteins. Both wild-type strain CH34 and aleB mutant AE1152 were able to use the same heterologous siderop hores, indicating that AleB is involved only in ferric iron-alcaligin E uptake, Interestingly, no utilization of pyochelin, which is also a phenolate-type siderophore, was observed for A. eutrophus CH34. Geneti c studies of different Sid(-) mutants, obtained after transposon mutag enesis, showed that the genes involved in alcaligin E and ferric iron- alcaligin E receptor biosynthesis are clustered in a 20-kb region on t he A. eutrophus CH34 chromosome in the proximity of the cys-232 locus.