Production of siderophore type chelates in Atlantic Ocean waters enriched with different carbon and nitrogen sources

Siderophore type chelates were detected in nutrient enriched, incubated seawater collected from different biogeographical regions of the Atlantic Ocean. Seawater was enriched with glucose and ammonium, glycine (as a source of carbon and nitrogen) or chitin and ammonium at different concentrations and was incubated for up to 3–4 days in the dark. Siderophore type chelates were detected using high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC–ICP–MS) after complexation with Ga. Samples were subsequently analysed by HPLC–electrospray ionisation mass spectrometry (HPLC–ESI–MS) in order to confirm the identity of the known siderophores, and to obtain the pseudo-molecular ions of unknown siderophore type chelates. A total of 22 different siderophore type chelates were resolved in the HPLC–ICP–MS chromatograms. Ten different siderophore type chelates were identified by HPLC–ESI–MS, 3 of which had not previously been identified in nutrient enriched seawater incubations. The concentration and diversity of siderophore type chelates was highest in seawater amended with glucose. The concentrations and diversity of siderophore type chelates also varied with biogeographical area in the Atlantic Ocean, with the North Atlantic Sub-tropical Gyre yielding highest concentrations in incubations, and the South Atlantic Sub-tropical Gyre and Western Tropical Atlantic yielding the highest diversity.

Research Highlights
► Siderophores are produced by marine microbes in order to acquire iron from seawater.
► Siderophores were detected by elemental and organic mass spectrometry.
► Different carbon sources were added to seawater to maximise siderophore diversity.
► Siderophores were produced by mixed microbial populations from the Atlantic Ocean.
► 23 different siderophores were detected in the study.