Effect of UV stress on the fatty acid and lipid class composition in two marine microalgae Pavlova lutheri (Pavlovophyceae) and Odontella aurita (Bacillariophyceae)
Résumé
Polyunsaturated fatty acids (PUFAs), especially eicosapentaenoic and docosahexaenoic acids (EPA and DHA), are abundantly synthesized by some phytoplankton species and play a key role in the marine food chain. However, they are generally considered to be sensitive to oxidation by UV radiation (UV-R). In order to investigate the effect of UV-R on the lipid composition of two marine microalgae, Pavlova lutheri and Odontella aurita, they were exposed to a combination of UVA-R and UVB-R with a total UV-R daily dose of 110 kJ m−2. Chlorophyll a, photochemical efficiency, and lipid composition were then determined on days 3, 5, and 8 of UV-R exposure. In P. lutheri, exposure to UV-R treatment led to a decrease in the proportions of PUFAs, such as EPA and DHA, especially into structural lipids (glycolipids and phospholipids). Our findings reveal a reduction of 20% in EPA levels and 16% in DHA levels, after 8 days of UV-R treatment. In O. aurita, exposure to UV-R did not change the fatty acid composition of the total lipids and lipid fractions of the cells. EPA levels remained high (27–28% of total lipids) during the 8 days of treatment. Consequently, the n-3 fatty acid content of P. lutheri was altered which highlights the sensitivity of this species to UV-R, whereas the results obtained for O. aurita suggest a more UV-R resistance. As a result, in latitude countries with medium UV-R level, outdoor “race-way” culture of O. aurita could yield a high-EPA algal biomass, whatever the seasonal variations in UV-R.