Additional file 7: Figure S5. of Ostreococcus tauri is a new model green alga for studying iron metabolism in eukaryotic phytoplankton

Effect of copper (A) and iron (B) on the growth rate of O. tauri and C. reinhardtii, and iron associated to the cells of both species as a function of iron concentration in the medium (C). A, B: O. tauri (red circles) and C. reinhardtii (black squares) cells were grown with a gradient of CuSO4 (0.01 nM-50 μM) and Fe(III)-citrate (1 nM-10 μM) concentrations as described in Methods. Results are expressed as a % of the maximal growth rate in exponential growth phase. Means ± SD from 4 experiments. C: Intracellular iron content was determined as described in Methods after growing O. tauri (red circles) and C. reinhardtii (black squares) for 5 days in the presence of 10 nM-10 μM 55Fe-ferric citrate (open symbols) or 55Fe(III)-EDTA (closed symbols)..Means ± SD from 3 experiments. The maximal growth rates of O. tauri and C. reinhardtii were reached with 50 nM and >1 μM iron in the medium, respectively (A). Copper also had very different effects on the growth of the two species: the addition of copper to the medium did not improve the growth of O. tauri (B), even when the cells were repeatedly used to re-inoculate copper-free medium (i.e. in medium with no added copper) over a period of several months. Thus, contaminating copper was sufficient to meet the copper requirements of the cells; when copper was added to the medium, it became toxic at concentrations greater than 1 μM (B). By contrast, the addition of copper to the medium at concentrations of up to 5 μM improved the growth of C. reinhardtii, and toxicity was observed only at concentrations exceeding this value (B). These striking differences probably reflect fundamental aspects of the iron-copper connection in the two species, and differences in the response of cells to iron deprivation.The iron content per cell volume was 10 to 100-fold greater in O. tauri than in C. reinhardtii, suggesting that the iron uptake systems of O. tauri are much more efficient than those of C. reinhardtii. (PPTX 272 kb