Ether lipid production in relation to growth in Botryococcus braunii

Abstract

A strain of Botryococcus braunii (A race) that synthesizes large amounts of an ether lipid mixture (botryococcoid ethers), dominated by a C54H100O2 compound, was grown in batch air-lift cultures in order to investigate the relationship between ether lipid production and growth. Ether lipid production appears particularly efficient in the exponential and early deceleration stages, constituting up to 42% of the dry biomass. In sharp contrast the alkadiene and triene levels—the characteristic hydrocarbons of the A race—remain very low throughout growth, especially when compared with that observed in all B. braunii strains previously studied. During growth, important changes occur in the hydrocarbon distribution, in particular regarding the quantities of a C27 triene. Moreover, an inverse relationship is observed between the amount of this triene (relative to total hydrocarbons) and ether lipid production. This result, joined to some structural considerations, suggested a precursor role for the C27 triene. As recently demonstrated in the A race, trienes do not originate from diene desaturation but from decarboxylation of diunsaturated very long-chain fatty acids, oleic acid being the direct precursor both in the diene and triene biosynthetic pathways. In the present strain, [10-14C] oleic acid was efficiently incorporated into ether lipids and hydrocarbons, thus demonstrating the existence of a close biogenetic relationship between these two types of compounds. Finally, a feeding experiment shows the incorporation of radioactivity from a mixture of 14C-labelled C27 trienes where the supposed precursor dominates. On the basis of our results, a biosynthetic mechanism is proposed with two mono epoxides derived from the triene as possible intermediates.