Effects of iron sources on the growth and lipid/carbohydrate production of marine microalga Dunaliella tertiolecta

The effects of iron sources with different speciation and anionic moieties (ferric chloride, ferrous chloride, ferric EDTA, ferrous EDTA, ferric ammonium sulfate, and ferrous ammonium sulfate) on the cell growth and the production of energy storage (lipid and carbohydrate) from Dunaliella tertiolecta were investigated. The influence of iron dosage was also compared in the range from 0.65 mg/L (1X) to 6.5 mg/L (10X) as Fe concentration. Best cell growth rate was achieved when ferrous ammonium sulfate was used. Ferric EDTA resulted in higher lipid content than other iron sources, while ferrous ammonium sulfate favored the accumulation of carbohydrate among six iron sources. The accumulations of lipid and carbohydrate as energy storage competed each other and thus both contents did not increase together. In the presence of ferric EDTA, lipid content is increasing, while carbohydrate content is decreasing. On the contrary, lipid content is decreasing while carbohydrate is increasing in the presence of ferric ammonium sulfate. Because the overall carbohydrate content was larger than that of lipid, bioethanol production would be more advantageous than biodiesel production with the present D. tertiolecta strain if the carbohydrate in D. tertiolecta contains a high fraction of glucose with a good saccharification yield.