Effect of growth temperature on the biosynthesis of eukaryotic lipid molecular species by the cyanobacterium Spirulina platensis.

The incorporation of linoleic acid added at mmolar concentrations to the culture medium of the photosynthetic prokaryote Spirulina platensis results in the synthesis of membrane glycerolipids with a eukaryotic distribution of fatty acid chain length on the glycerol backbone (Pham Quoc et al., Biochim. Biophys. Acta [1993] 1168, 94-99). This distribution contrasts with the usual prokaryotic one found in lipids of cyanobacteria. A subsequent desaturation of the exogenously supplied fatty acid resulted in a large increase of gamma-linolenic acid. In order to estimate the capacities of S. platensis for bioconversion of fatty acids in lipid classes, the effects of different temperatures of growth were studied in linoleic acid-supplemented cultures. The lipid composition was affected by growth temperature, the synthesis of SQDG was stimulated at low temperature. The molecular species of each lipid were isolated and analyzed. Whatever the temperature of growth, the biosynthesis of eukaryotic C18/C18 lipid molecular species was observed in all lipid classes. Furthermore, the proportion of eukaryotic lipids increased at low temperature (24 degrees C). The desaturation of C18 fatty acids at C1 and C2 positions of the glycerol moiety occurred and was further stimulated when the growth temperature was lowered. The resulting proportion of gamma-linolenic acid increased significantly in cultures supplemented with linoleate at low temperatures. Finally a pathway for the synthesis of eukaryotic lipids and the desaturation of fatty acids esterified to the acyl lipids of linoleate-supplemented S. platensis can be suggested.