Amino acid variability in the peptide composition of a suite of amphiphilic peptide siderophores from an open ocean Vibrio species

In response to iron deplete aerobic conditions, bacteria often secrete low molecular weight, high-affinity iron(III)-complexing ligands, siderophores, to solubilize and sequester iron(III). Many marine siderophores are amphiphilic and are produced in suites, wherein each member within a particular suite has the same iron(III)-binding polar head group which is appended by one or two fatty acids of varying length, degree of unsaturation and hydroxylation, establishing the suite composition. We report herein the isolation and structural characterization of a suite of siderophores from marine bacterial isolate Vibrio sp. Nt1. Based on structural analysis, this suite of siderophores, the moanachelins, is amphiphilic and composed of two N-acetyl, N-hydroxy D-ornithines, one N-acetyl, N-hydroxy L-ornithine and either a glycine or an L-alanine, appended with various saturated and unsaturated fatty acid tails. The variation in the small side-chain amino acid is the first occurrence of variation in the peptidic head group structure of a set of siderophores produced by a single bacterium