Effects of light intensity, CO2 and nitrogen supply on lipid class composition of Dunaliella viridis

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Lipid class composition of Dunaliella viridis Teodoresco was analysed using thin layer chromatography coupled with flame ionisation detection (TLC/FID technique). D. viridis was cultured under four different photon fluence rates and in darkness, and under two different conditions of CO2 supply (atmospheric and 1%) with and without nitrogen sufficiency. Nine lipid classes were identified and quantified. Total lipids per cell and acetone-mobile polar lipids decreased with light, while the percentage of sterols and triglycerides increased with increasing irradiance. Total phospholipids increase was related with growth rate while hydrocarbons, wax esters and sterol esters accumulated in darkness. There were almost no changes in total lipids per cell because of nitrogen limitation; however, nitrogen limitation led to higher changes in lipid class composition under 1% CO2 than under atmospheric CO2 levels. The main reserve lipid, triglycerides, accumulated in high amounts under 1% CO2 and nitrogen limitation, increasing from 1% to 22% of total lipids. The ratio sterols/acetone-mobile polar lipids could be an index of the ‘light status’ independently of nitrogen limitation, while the ratio triglycerides/total phospholipids could indicate any physiological stress uncoupling C and N metabolism and affecting the growth rate.

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