Additional file 14: Figure S12. of Ostreococcus tauri is a new model green alga for studying iron metabolism in eukaryotic phytoplankton

Comparison of ferritin iron loading in O. tauri and C. reinhardtii. Cells of the two species (including the ferritin KO mutant of O. tauri, used as a control) were cultured as described in the methods, with different concentrations of Cu (−: no Cu added; +: 0.1 μM (O. tauri) or 1 μM (C. reinhardtii) CuSO4) and Fe (−: 1 nM (O. tauri) or 50 nM (C. reinhardtii) ferric citrate; +: 1 μM ferric citrate). After 5 days, the cells were harvested, and resuspended in iron-free Mf medium (O. tauri) or iron-free TAP medium (C. reinhardtii) supplemented with 5 μM 55Fe(III)-citrate. The cells were incubated for 3 h and then harvested by centrifugation. Whole-cell extracts were obtained and subjected to native PAGE (25 μg/lane), as described in the methods. A comparison of autoradiographs of dried gels shows that O. tauri ferritin was maximally loaded with iron when the cells had previously been grown in iron-rich conditions, whereas the main ferritin of C. reinhardtii was maximally loaded with iron when the cells were grown in iron-deficient conditions. The addition of Cu to the medium resulted in some intracellular iron redistribution in O. tauri (although Cu did not affect iron uptake): a band that we previously identified as a probable nitrate reductase (Botebol et al.) was more intense in the presence of copper. We are currently characterizing this band further. (PPTX 3065 kb