Isolation and structure elucidation of acinetobactin., a novel siderophore from Acinetobacter baumannii

A novel siderophore, called acinetobactin, with both catecholate and hydroxamate functional groups was isolated from low-iron cultures of Acinetobacter baumannii ATCC 19606. The structure was elucidated by chemical degradation, fast-atom bombardment mass spectrometry and ¹H and ¹³C NMR spectroscopy. Acinetobactin was composed of -N-hydroxyhistamine, threonine and 2,3-dihydroxybenzoic acid, the last two components forming an oxazoline ring. Acinetobactin was structurally related to anguibactin, a plasmid-encoded siderophore of Vibrio anguillarum. The only difference was that acinetobactin possessed an oxazoline ring instead of a thiazoline ring. Four of 12 other clinical A. baumannii strains examined produced acinetobactin, indicative of strain-to-strain variation in the ability to produce acinetobactin. In addition, a relatively small amount of acinetobactin was also detected in A. haemolyticus ATCC 17906.Abbreviations COSY chemical shift correlation spectroscopy - DHBA 2,3-dihydroxybenzoic acid - EDDA ethylenediamine-di(o-hydroxyphenylacetic acid) - FAB fast-atom bombardment - GC-MS gas chromatography-mass spectrometry