Inducing lipid accumulation in microalgae cells without suppressing cell growth is vital to the economical production ofbiodiesel from microalgae. In two experiments, we demonstrate that the eel1 concentration and lipid content of marine microalgae Isochrysis galbana depend upon the iron concentration in the growth media. In Experiment I, adding chelated FeC13 to the medium at the late exponential growth phase prolonged this phase and increased the lipid content in I. galbana cells. The final cell density and lipid content of I. galbana supplemented with chelated FeC13 was approximately 2 and 1.65 times higher than that of non-supplemented cultures, respectively. In Experiment II, I. galbana cells in the late exponential phase were collected and re-inoculated into new media containing Fe3＋ at various concentrations. The final cell concentration and lipid content were maximized at the highest iron concentration （38% biomass by dry weight at 1.2×10^-5 mol/L Fe3＋）. In this study, intracellular neutral lipid storage was evaluated by fluorescent spectrophotometry using fluorochrome Nile red, and the measurement conditions were optimized.
