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 Halomonas aquamarina strain DS40M3, and the marinobactins, from Marinobacter 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.

Production of siderophores by marine bacteria could potentially contribute to metal complexation by organic compounds in seawater. Direct isolation of planktonic marine bacteria on siderophore indicator plates showed that siderophore producers are present. The siderophore‐producing organisms that could be detected on this medium were more numerous in the mixed layer than in deeper water at this sampling site. One strain (DS40M5) was characterized and found to be a marine Vibrio sp. A siderophore produced by Vibrio sp. DS40M5 is aerobactin, a compound not previously known from planktonic marine bacteria.

Marine bacterial isolates Vibrio sp. HC0601C5 and Halomonas meridiana str. HC4321C1 were isolated off the coast of southern California and were found to produce an expanded suite of previously identified amphiphilic siderophores. Specifically two new members of the amphibactin family, amphibactins S and T, which have a C14:1 ω-7 fatty acid and a saturated C12 fatty acid, respectively, were produced by Vibrio sp. HC0601C5. These siderophores are produced in addition to a number of previously described amphibactins and are excreted into the culture supernatant. Two new members of the aquachelin family of siderophores, aquachelins I and J, which have an hydroxylated C12 fatty acid and a saturated C10 fatty acid, respectively, were produced by Halomonas meridiana str. HC4321C1. These four new siderophores are more hydrophilic than their previously reported relatives, aquachelins A–D and the amphibactin suite of siderophores.

The coordination of iron(III) to the marine amphiphilic marinobactin and aquachelin siderophores, as well as to petrobactin, the unusual 3,4-dihydroxybenzoyl siderophore is reported. Potentiometric titrations were performed on the apo siderophore to determine the ligand pK a values,

No abstract