Abstract: Objectives: To study the effects of nitrogen and phosphorus concentrations on the growth and total lipids (TL) arachidonic acid (AA) contents of Myrmecia incise and to analyze fatty acid composition under low nitrogen and low phosphorus conditions. Methods: M. incise was grown in a glass column photobioreactor (φ 6 × 60 cm) with BG-11 medium under different concentrations of nitrogen and phosphorus (one element was fixed and the other was varied at three different levels). Lipid extraction was achieved using organic solvent extraction. GC-MS was used for fatty acid composition analysis. Results: Within the range of 300－1500 mg/L, varying NaNO3 concentration had unobvious effect on the biomass of M. incise, which was correspondingly between 2.10 g/L and 2.40 g/L. The highest TL (27% of the dry weight of M. incise) and AA contents (9.04% of the total fatty acids, and 3.16% of the dry weight of M. incise) were obtained under low nitrogen conditions. When varying from 8 to 40 mg/L, phosphorus concentration could distinctly affect the growth of M. incise, a dramatic inhibitory effect was observed under low phosphorus conditions and the resulting biomass was 0.98－2.47 g/L. TL content had little change and fluctuated around 20% when the phosphorus concentration was increased from 8 to 20 mg/L. Conclusions: TL content of M. incise was highly negatively correlated with nitrogen or phosphorus concentrations. M. incise is easier to accumulate AA under low nitrogen conditions when compared to low phosphorus.

Key words: Myrmecia incise, nitrogen concentration, phosphorus concentration, fatty acids, total lipids, arachidonic acid