Effect of growth rate on the eicosapentaenoic acid and docosahexaenoic acid content of Isochrysis galbana in chemostat culture

An isolate of Isochrysis galbana rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) has been grown as a chemostat culture at 20° C and pH 8.00 controlled by CO₂ injection. From a low dilution rate (D) of 0.0024 h^–1 to 0.0377 h^–1, close to maximum growth, a decrease in EPA content from 5.21% dry weight (d.w.) to 2.80% d.w. was observed, although the percentage of EPA in the total fatty acids increased. Lipids were fractionated, EPA being the major fatty acid found in the glycolipid fraction, whereas in the neutral lipid fraction were mainly palmitic and palmitoleic acids. At the same time, the biomass concentration also decreased from 1015 mg·l^–1 to 202 mg·l^–1 over the range of Ds mentioned. Nonetheless, EPA productivity had a maximum value of 15.26 mg·l^–1·day^–1 at D=0.0208 h^–1.Correspondence to: E. Molina Grima