Detection of hydroxamate siderophores in coastal and Sub-Antarctic waters off the South Eastern Coast of New Zealand

In this study, we report siderophore-type compounds found in coastal and Sub-Antarctic waters within a 60 km transect off the south east coast of Otago Peninsula in New Zealand. The presence of siderophore activity was detected using chrome azurol S assay (CAS) from organic compounds extracted from similar to 200 to 480 L seawater by pre-concentration on XAD-16 resin. Csaky and Rioux assays indicated the presence of more than one functional type of siderophore or siderophore-like compound. Strong Fe-binding ligand (L-1) concentrations, the sum of ligands (Sigma L). and their stability constants were measured from ambient seawater samples using competing ligand equilibration-cathodic stripping voltammetry (CLE-CSV). In the study area L-1 ranged from 0.23 to 0.69 nM (logK'(FeL1.Fe3+) = 22.0-22.8), whereas Sigma L values ranged from 0.53 to 1.23 nM (logK'(Fe Sigma L.Fe3+) = 21.4-22.2). Dissolved Fe (DFe) concentrations were measured by CSV and ranged from 0.22 to 0.45 nM. This is the first application of a new liquid chromatography-tandem mass spectrometry method using the natural iron-isotope pattern to characterize siderophore-type compounds isolated from natural seawater. Altogether six siderophore-type compounds with hydroxamate functionality were detected in one coastal, as well as Sub-Antartic surface and subsurface samples. This new method and the derived results provide a foundation for future investigations of sources and structures of strong ligands in the Southern Ocean and elsewhere. (C) 2011 Elsevier B.V. All rights reserved.