Loihichelins A−F, a Suite of Amphiphilic Siderophores Produced by the Marine Bacterium Halomonas LOB-5

Abstract

A suite of amphiphilic siderophores, loihichelins A−F, were isolated from cultures of the marine bacterium Halomonas sp. LOB-5. This heterotrophic Mn(II)-oxidizing bacterium was recently isolated from the partially weathered surfaces of submarine glassy pillow basalts and associated hydrothermal flocs of iron oxides collected from the southern rift zone of Loihi Seamount east of Hawai’i. The loihichelins contain a hydrophilic headgroup consisting of an octapeptide comprised of d-threo-β-hydroxyaspartic acid, d-serine, l-glutamine, l-serine, l-N(δ)-acetyl-N(δ)-hydroxyornithine, dehydroamino-2-butyric acid, d-serine, and cyclic N(δ)-hydroxy-d-ornithine, appended by one of a series of fatty acids ranging from decanoic acid to tetradecanoic acid. The structure of loihichelin C was determined by a combination of amino acid and fatty acid analyses, tandem mass spectrometry, and NMR spectroscopy. The structures of the other loihichelins were inferred from the amino acid and fatty acid analyses and tandem mass spectrometry. The role of these siderophores in sequestering Fe(III) released during basaltic rock weathering, as well as their potential role in the promotion of Mn(II) and Fe(II) oxidation, is of considerable interest.