Primary productivity in 30-40% of the world’s oceans is limited by availability of the micronutrient iron. Regions with chronically low iron concentrations are sporadically pulsed with new iron inputs via dust or lateral advection from continental margins. Addition of iron to surface waters in these areas induces massive phytoplankton blooms dominated primarily by pennate diatoms. We recently discovered that the bloom-forming pennate diatoms Pseudo-nitzschia and Fragilariopsis use the iron-concentrating protein, ferritin, to safely store iron. This is the first description of ferritin in any member of the Stramenopiles, a diverse Eukaryotic lineage that includes unicellular algae, macroalgae and plant parasites. Phylogenetic analyses suggest that ferritin may have arisen in this small subset of diatoms via a lateral gene transfer. The crystal structure and functional assays of recombinant ferritin derived from Pseudo-nitzschia multiseries reveal a maxi-ferritin that exhibits ferroxidase activity and binds iron. The protein is predicted to be targeted to the chloroplast to control the distribution and storage of iron for proper functioning of the photosynthetic machinery. Abundance of Pseudo-nitzschia ferritin transcripts is regulated by iron nutritional status and is closely tied to the loss and recovery of photosynthetic competence. Enhanced iron storage with ferritin allows the oceanic diatom Pseudo-nitzschia granii to undergo several more cell divisions in the absence of iron than the comparably sized, oceanic centric diatom Thalassiosira oceanica. Ferritin in pennate diatoms likely contributes to their success in chronically low iron regions that receive intermittent iron inputs and provides an explanation for the importance of these organisms in regulating oceanic CO2 over geological timescales.
Our results were recently published in the journal Nature:
Additional links discussing our findings are provided below:
1) Recommended Paper – Faculty of 1000
2) Putting the Bloom on the Diatom - Canadian Light Source Inc.
3) Marine Diatoms Survive Iron Droughts in the Ocean by Storing Iron in Ferritin - Stanford Synchrotron Radiation Lightsource