Effect of culture conditions on growth, fatty acid composition and DHA/EPA ratio of Phaeodactylum tricornutum

Abstract

The effect of growth phase and environmental factors on growth, fatty acid composition and DHA/EPA ratio of Phaeodactylum tricornutum Bohlin was studied. Microalgae were grown in laboratory batch cultures in f/2 medium. Cultures were grown at different salinities (15, 20, 28, and 35ppt), nitrogen (N) concentrations (1.24, 12.35, 24.70 and 49.40mgL−1), light intensities (50, 100 and 150μmolm−2s−1; 14:10h light:dark cycle) and temperatures (15, 20 and 25°C), and sampled at different points of the respective growth phases (inoculums, early-linear, middle-linear and late-linear phases). Samples were analyzed for biomass weight, fatty acid composition and total fatty acid content (TFAC). The main fatty acids in all culture conditions were C14:0 (5.25%–6.04%), C16:0 (13.96%–14.78%), C16:1n-7 (19.09%–35.73%), C18:1n-9 (5.56%–9.01%) and eicosapentaenoic acid (EPA, 22.81%–30.72%). The percentage of polyunsaturated fatty acids (PUFAs) was reduced while that of monounsaturated fatty acid acids (MUFAs) and TFACs increased with culture time. Salinity had no serious effect on fatty acid composition, however, a significant decline of TFAC was observed at the lowest salinity (p<0.05). Significant (p<0.05) increases of the relative contents of SFAs and MUFAs and a decrease of PUFAs were observed under N-limitation condition. The percentage of docosahexaenoic acid (DHA) was significantly enhanced with increasing light intensity (p<0.05), while that of DHA, EPA and PUFA decreased significantly with increasing temperature (p<0.05). DHA/EPA ratio tended to rise initially and fall later with increasing growth time, and reached the highest level with the lowest salinity, and the lowest temperature and initial N concentration, revealing a possible cell response to the stress brought from the unfavorable conditions. In conclusion, this study demonstrates the variation of growth, fatty acid composition and DHA/EPA ratio with growth phase and environmental factors in P. tricornutum, benefiting the production of PUFA-rich microalgae, with a DHA/EPA ratio optimal for aquaculture live food. Statement of relevanceWe conducted detailed analysis on the effect of the culture conditions on growth, fatty acid composition and DHA/EPA ratio in Phaeodactylum tricornutum, a widely used microalga for aquaculture feedstuff in China. We found that the environmental stress conditions increased DHA/EPA ratio. The research will benefit the production of PUFA-rich and DHA/EPA-ratio-optimal microalgae for aquaculture feedstuff.