Lipid accumulation and eicosapentaenoic acid distribution in response to nitrogen limitation in microalga Eustigmatos vischeri JHsu-01 (Eustigmatophyceae)

Abstract

Eicosapentaenoic acid (C20: 5; EPA) is one of the important ω−3 long-chain polyunsaturated fatty acids for human health, found in various microalgal species. However, the mechanisms behind the distribution of EPA in lipid molecules have not been well established. An oleaginous microalga, Eustigmatos vischeri, has been considered as a potential producer of EPA. The present study was aimed at investigating the lipid accumulation and EPA distribution in E. vischeri JHsu-01 under nitrogen-limited and nitrogen-replete conditions. The results showed that nitrogen limitation could substantially restrict the growth of the microalga and inhibit EPA synthesis, but enhance the accumulation of neutral lipids. E. vischeri JHsu-01 distributed more EPA into the membrane lipids under nitrogen-replete conditions, whereas those under nitrogen-limited conditions tended to allocate EPA into storage lipids. Besides, the expression level of several key enzymes for linoleic acid synthesis was up-regulated under nitrogen-limited conditions. The expression level of fatty acid desaturase, involving Δ5, Δ6 and Δ15 desaturases decreased, which was responsible for decreasing EPA content under nitrogen-limited conditions. Eicosapentaenoic acid derived from inter-esterification of membrane lipids may participate in synthesizing triacylglycerol via catalysis of phospholipid: diacylglycerol acyltransferase, resulting in high levels of EPA for storage lipids. The present study highlighted the importance of nitrogen regulation during the cultivation of microalga to induce EPA production in E. vischeri JHsu-01. Specifically, EPA distribution within the individual lipid fractions was not solely restricted by the genetics profiles of microalgae, but also altered by available nitrogen concentrations. CapsuleSynthesis and distribution of eicosapentaenoic acid are affected by nitrogen supply.