Fig 1.

N⁵-Acyl-N⁵-hydroxyornithine units observed for known fungal siderophores; R can be any of the known residues shown in diagrams a to i (10). An example structure (by adding the moiety f to the N⁵-hydroxyornithine unit) is shown on the right. The asterisk indicates the polar acyl or ester/peptide bond, the cleavage of which results in either the moiety shown in capital letters or the moiety shown in capital letters and “‡.” The cleavage of these moieties results in characteristic siderophore fragments found in tandem mass spectrometry (see Table S2 in the supplemental material).