High CO2 increases lipid and polyunsaturated fatty acid productivity of the marine diatom Skeletonema costatum in a two-stage model

Lipid and polyunsaturated fatty acids (PUFA) from microalgae can be used as biodiesel and health care products. How to enhance their productivity is crucial for successful commercial production. In this study, a two-stage model was used to stimulate the production of lipids and PUFA in a bloom-forming marine diatom Skeletonema costatum . Cells were cultured in ambient air (0.04% CO 2 ) in the first stage and transferred to two high CO 2 levels (5% and 10%) in the second stage. The medium CO 2 level (5%) increased both specific growth rate and lipid content and hence almost doubled lipid productivity compared to 0.04% CO 2 level. Although a 10% CO 2 level induced the highest lipid content, it had negative effects on the specific growth rate and soluble carbohydrate synthesis, and the lipid productivity was not as high as 5% CO 2 . Neither CO 2 level affected the cell size, chlorophyll a content, or soluble protein content. High CO 2 levels also increased the synthesis of PUFA, e.g., eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Although high CO 2 levels increased iodine value and decreased the cetane number of oil exacted from S. costatum , they fall in the range of the European standard, suggesting its suitability for biodiesels. These findings indicate that a two-stage model with high CO 2 induction is an effective approach for the production of biodiesel and PUFA from S. costatum , which could be used in both biofuel and health care markets.