Effects of Different Culture Conditions on the Synthesis and Distribution of Polyunsaturated Fatty Acids (EPA and ARA) in Porphyridium purpureum

The arachidonic acid (C20:4 ω6, ARA) and eicosapentaenoic acid (C20:5 ω3, EPA) from Porphyridium purpureum endow this microalga with potential utilization value, but their distribution patterns remain poorly understood. In this study, a nitrogen concentration, a phosphorus concentration, light intensity and salinity were applied to investigate the synthesis and distribution patterns of EPA and ARA in P. purpureum by measuring growth, lipid content, lipid fractions, fatty acid composition, and the levels of EPA and ARA in storage lipids and membrane lipids. The results show that the optimal conditions for biomass accumulation were a nitrogen concentration of 0.75 g L−1, a phosphorus concentration of 240 mg L−1, a light intensity of 250–300 μmol photons m−2 s−1 and a salinity of 50 ppt. Reducing the phosphorus concentration and increasing salinity enhanced the total lipid content, whereas changes in nitrogen concentration and light intensity had minimal effects on total lipid content. Low nitrogen concentration, low phosphorus concentration and high light intensity favored ARA synthesis, whereas the opposite conditions promoted EPA synthesis. Culture conditions could alter the distribution of ARA and EPA between storage lipids and membrane lipids. Increasing the nitrogen concentration, phosphorus concentration and salinity, as well as reducing light intensity, promoted the distribution of ARA and EPA in membrane lipids. Conversely, the opposite conditions enhanced their distribution in storage lipids. In conclusion, the synthesis and distribution of EPA and ARA in P. purpureum are influenced by culture conditions. To improve the yield of ARA and EPA, P. purpureum should be cultivated under nutrient-sufficient conditions.