The green alga Nannochloropsis sp. QII was cultivated in media with sufficient and growth‐limiting levels of nitrogen (nitrate). Nitrogen deficiency promoted lipid synthesis yielding cells with lipids comprising 55% of the biomass. The major lipids were triacylglycerols (79%), polar lipids (9%) and hydrocarbons (2.5%). The polar lipids consisted of a broad range of phospholipids, glycolipids and sulfolipids. Other lipids identified were pigments, free fatty acids, saponifiable and unsaponifiable sterol derivatives, various glycerides, a family of alkyl‐1, 4‐dioxane derivatives and a series of alkyl‐ and hydroxyalkyl‐dimethyl‐acetals. Experiments in which 14CO2 was provided at different times in the growth cycle demonstrated that enhanced lipid biosynthesis at low nitrogen levels resulted principally from de novo CO2 fixation.

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