HIGH-RATES OF LIPID BIOSYNTHESIS IN CULTURED, MESOCOSM AND COASTAL POPULATIONS OF THE COCCOLITHOPHORE EMILIANIA-HUXLEYI

The patterns of carbon incorporation into proteins, polysaccharides, lipids and low molecular weight metabolites and the resulting cellular biochemical composition were examined within cultured and natural populations of the coccolithophore Emiliania huxleyi. The flows of carbon incorporated through photosynthesis were primarily directed towards the synthesis of lipids (40 to 60%), mainly neutral lipids, whereas relative carbon incorporation into proteins was low (ca 20%), regardless of irradiance levels or growth stage. Actively dividing E. huxleyi cells showed higher rates of carbon incorporation into protein during darkness than during the previous light period, whereas under energy-limited growth conditions proteins produced during the light period were catabolized in darkness. The observed C-14 labelling patterns were consistent with both the measured biochemical composition of E. huxleyi cells growing in cultures under the same conditions and with that of coccolithophore-dominated natural phytoplankton assemblages. The relative decrease in cellular density caused by a lipid-rich composition could be significant for the buoyancy of cells and, consequently, for the dynamics of blooming events. Furthermore, the high-lipid, low-protein metabolism characteristic of this species implies an increase of carbon uptake relative to nitrogen that would, to some extent, counteract the enhancing effect of calcification on the partial pressure of CO2 typical of blooms of E. huxleyi.