Light-dependent utilization of two radiolabelledcarbon sources, sodium bicarbonate and sodiumacetate, and relationships with long chainpolyunsaturated fatty acid synthesis in the microalgaPavlova lutheri (Haptophyta)

摘要

Pavlova lutheri is a common member of the Pavlovophyceae (Haptophyta), often used as a food source for aquatic filterfeedersand cultured in laboratories to produce high levels of polyunsaturated fatty acids (PUFAs), especially eicosapentaenoicand docosahexaenoic acids (EPA and DHA, respectively), which are known to have benefits for human health. Consequently,we investigated the pathways involved in the biosynthesis of long chain polyunsaturated fatty acids (LC-PUFAs) in this algaduring photosynthesis in relation to light intensity. Using two radiolabelled carbon sources, [14C] sodium bicarbonate and[1-14C] sodium acetate, we obtained data suggesting that P. lutheri is able to synthesize LC-PUFAs by successive elongationand desaturation steps. It converts palmitic acid into palmitoleic acid by D7-desaturation. Moreover, significant incorporationof [1-14C] acetate (organic carbon) and its subsequent use in lipid metabolism suggest that P. lutheri may have a mixotrophiccapacity for carbon assimilation. Synthesis of lipids, including galactolipids and phospholipids, increased with light intensitywhen the cells were incubated with [14C] bicarbonate (inorganic carbon), but was less sensitive to differences in light intensitywhen incubated with [1-14C] acetate, a heterotrophic carbon source that stimulates the synthesis of monounsaturated fattyacids, such as oleic acid. In the case of n-3 fatty acids, EPA and DHA synthesis was lower at high light (340 mmolphotons m2 s1) with the [14C] bicarbonate, but did not vary with [1-14C] acetate. Finally, P. lutheri seems to have two distinctenzyme pools involved in LC-PUFA synthesis, one is intra-chloroplastidic and dependent on light intensity, and the other isextra-chloroplastidic and independent of light.