Accumulation of fatty acids in Chaetoceros gracilis (Bacillariophyceae) during stationary growth phase

Marine microalgae, Pavlova lutheri, Tetraselmis tetrathele, and Chaetoceros gracilis, were cultured for some time during the stationary growth phases, respectively, although they are generally harvested as live feed around the early stationary growth phases. Their fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were periodically analyzed during the culture periods, and thus evaluated the effect of the prolonged culture period on the accumulation of fatty acids in each microalga. By culturing P. lutheri longer than the ordinary harvest time, a slight increase was observed in the combined contents of EPA and DHA after reaching the stationary growth phase, while the prolongation of the culture period was not effective for T. tetrathele. On the other hand, C. gracilis accumulated the fatty acids rapidly and largely during the stationary growth phase and thus increased the combined contents of EPA and DHA, although their relative percentages decreased with the culture time. At later stationary growth phase of C. gracilis, the total fatty acid content and the combined contents of EPA and DHA were about eight and four times larger than those at the late exponential growth phase, respectively, and were the largest among all the samples examined. Therefore, prolonging the culture period after reaching the stationary growth phase will be advantageous at least for the harvest of C. gracilis enriched in fatty acids including EPA and DHA.