Influence of siderophore-iron complexation on the growth of the diatom Skeletonema costatum: a mass spectroscopy approach
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- Institutt for kjemi 
The growth of the diatom Skeletonema costatum was monitored using in vivo fluorescence under concentration gradients of desferrioxamine B (DFB) and enterobactin to test the siderophores effect on iron bioavailability. Changes in the composition of dissolved organic matter, including the added siderophores, were then identified using HPLC-MS. Samples for organic matter analysis were taken once when the diatom reached exponential growth in all siderophore conditions.Previous research into the effect of siderophores on algal growth has indicated positive or negative growth of the diatom depends on both the diatom species and the type of siderophore. In this project, DFB inhibited growth at first, but eventually the diatom entered exponential phase growth even at the highest concentration of added DFB, 10 μM. Enterobactin showed less concentration dependent limitation of iron bioavailability and in lower concentrations showed an increase in growth compared to the control. The findings suggest that its ability to act as an iron scavenger in seawater is inhibited by its hydrophobicity.From compound ions found using MS, a range of potential iron chelators was detected. The siderophores were successfully identified along with DFB s complex with iron, ferrioxamine. Potential DFB metabolites matched predicted mass to charge ratios and chemical formulas but could not be confirmed structurally by the MS databases used. Saccharides, potential iron chelators released by algae, were also discovered. In the DFB series, the abundances of compound ions were significantly different based on the concentration of siderophore in the sample.The results of this project represent a snapshot of the dissolved organic matter present in samples. Further experiments tracking siderophores along with a few known chelators throughout diatom growth would enhance understanding of the role of chelators in diatom iron uptake. HPLC-MS is a promising technique to uncover the relationship between iron chelators and diatoms.