<jats:p> Most aerobic bacteria secrete siderophores to facilitate iron acquisition. Two families of siderophores were isolated from strains belonging to two different genera of marine bacteria. The aquachelins, from <jats:italic>Halomonas aquamarina</jats:italic> strain DS40M3, and the marinobactins, from <jats:italic>Marinobacter</jats:italic> sp. strains DS40M6 and DS40M8, each contain a unique peptidic head group that coordinates iron(III) and an appendage of one of a series of fatty acid moieties. These siderophores have low critical micelle concentrations (CMCs). In the absence of iron, the marinobactins are present as micelles at concentrations exceeding their CMC; upon addition of iron(III), the micelles undergo a spontaneous phase change to form vesicles. These observations suggest that unique iron acquisition mechanisms may have evolved in marine bacteria.