Genetic engineering of nannochloropsis salina and optimization of cultivation conditions for enhancing EPA production

Abstract

Microalgae are promising resources for producing biofuels and value-added products due to their rapid growth rate and high lipid content. In particular, the production of eicosapentaenoic acid (EPA) from microalgae as health supplements has gained more attention. The raw material for EPA production which are supplied from fish oil has reached its limit, thus the microalgae are required to be supplied as substrate resource. In this study, we did strain development and optimization of cultivation conditions for enhancing EPA production in Nannochloropsis salina. The genetic engineering of N. salina was performed through two strategies. First, we overexpressed malic enzyme (NsME) and investigated its effect on lipid productivity in N. salina. We successfully obtained transformant (ME2-13) with overexpressed NsME, which showed improved EPA productivity by up to 12%. Secondly, we performed overexpression of fatty acid elongase genes (FAE) involved in EPA synthesis pathway to improve the EPA content. However, no significant change in EPA content was observed in transformants. To further enhance EPA production, optimization of cultivation conditions using Response Surface Methodology (RSM) was conducted by focusing on two crucial cultivation parameters which are nitrogen concentration and temperature. EPA productivity of WT N. salina was improved under unstressed conditions (1.28 g/L, $21^circC$). Finally, the cultivation of ME2-13 was conducted in optimized conditions, leading to EPA productivity up to 2-fold compared to previous cultivation conditions. These results are expected to contribute to the commercialization of value-added products from microalgae.