The effect of growth temperature and culture density on the molecular species composition of the galactolipids in the red microalga Porphyridium cruentum (Rhodophyta)

The effects of biomass concentration and growth temperature on the molecular species composition of the major galactolipids of the red microalga Porphyridium cruentum Nag. were determined. At lower biomass concentrations, the Delta 17 desaturation of arachidonic acid to eicosapentaenoic acid (20:5) was enhanced in both prokaryotic-type and eukaryotic-type molecular species of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol. We suggest that chloroplastic Delta 17 desaturation is com-elated with the availability of light. A reduction in the growth temperature led to an increase in the proportion of the eukaryotic molecular species of MGDG, especially for 20:5/20:5 MGDG. These results suggest that this molecular species, and perhaps eukaryotic molecular species in general, may play a rob in the adaptation of cells to low growth temperatures.