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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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The neutral lipids of nine species of methanogenic bacteria including five methanobacilli, two methanococci, a methanospirillum, one methanosarcina as well as two thermoacidophilic bacteria, Thermoplasma and Sulfolobus, were analyzed. The major components were C30, C25 and/or C20 acylic isoprenoid hydrocarbons with a continuous range of hydroisoprenoid homologues. The range of acyclic isoprenoids detected were from C14 to C30. Apart from Methanosarcina barkeri, squalene and/or hydrosqualene derivetives were the predominant components in all species studied. The components of Methanosarcina barkeri were a family of C25 homologues. The distribution of the neutral lipid components and their specific variations in relative intensities emphasized the differences between the test organisms while the generic nature of the isoprenoid hydrocarbons demonstrated similarities between the diverse bacteria. The neutral lipid compositions from these bacteria, many of which exist in environmental conditions like those described for the various evolutionary stages of the archean ecology, resemble the isoprenoid distribution isolated from ancient sediments and petroleum. Therefore, these finding may have major implications to biological and biogeochemical evolution.