Triacylglycerol accumulation and change in fatty acid content of four marine oleaginous microalgae under nutrient limitation and at different culture ages.

Alteration of lipid biosynthesis is one of important biochemical changes when oleaginous microalgae grow under varied environmental conditions. The effects of culture age and nutrient limitation on triacylglycerol (TAG) accumulation and fatty acid content were investigated in four eicosapentaenoic acid (EPA)-rich marine microalgae. The amounts of TAGs in Chaetoceros sp., Phaeodactylum tricornutum and Nannochloropsis oculata increased sharply from day 4 to day 11, and then the former two remained nearly unchanged while the latter declined gradually during the batch culture. In contrast, no marked increase in TAG accumulation was observed in Pavlova viridis during the culture. Changes in total fatty acid (TFA) content mirrored those observed for TAG accumulation, while the EPA content reached a maximum generally at day 7 or 11 in the range of 11 - 32 mg g(-1) dry cell weight (DCW) and then declined. Nitrogen limitation led to a gradual increase in the amounts of TAGs from N. oculata pronouncedly but almost no change in other three species. The TFA content of the cultures after 5 days of nitrogen limitation was nearly twice that after 1 day in Chaetoceros sp., P. tricornutum and P. viridis, while the lowest increase (220 - 283 mg g(-1) DCW) was observed in N. oculata. TAGs increased gradually under phosphorus limitation in all four species but not sharply compared with that under nitrogen limitation in N. oculata. The TFA content increased gradually under phosphorus limitation and after 5 days of phosphorus limitation it was 1.5 - 2 times that after 1 day. The EPA content was generally not significantly affected by nitrogen or phosphorus limitation. Culture age and nutrient limitation could be useful variables for optimizing TAG accumulation and fatty acid content with potential for biodiesel production.