FERRIC IRON UPTAKE IN ERWINIA-CHRYSANTHEMI MEDIATED BY CHRYSOBACTIN AND RELATED CATECHOL-TYPE COMPOUNDS

Erwinia chrysanthemi 3937 possesses a saturable, high-affinity transport system for the ferric complex of its native siderophore chrysobactin, [N-alpha-(2,3-dihydroxybenzoyl)-D-lysyl-L-serine]. Uptake of Fe-55-labeled chrysobactin was completely inhibited by respiratory poison or low temperature and was significantly reduced in rich medium. The kinetics of chrysobactin-mediated iron transport were determined to have apparent K(m) and V(max) values of about 30 nM and of 90 pmol/mg . min, respectively. Isomers of chrysobactin and analogs with progressively shorter side chains mediated ferric iron transport as efficiently as the native siderophore, which indicates that the chrysobactin receptor primarily recognizes the catechol-iron center. Free ligand in excess only moderately reduced the accumulation of Fe-55. Chrysobactin may therefore be regarded as a true siderophore for E. chrysanthemi.