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

The patterns of carbon incorporation into proteins, polysaccharides, l ipids and low molecular weight metabolites and the resulting cellular biochemical composition were examined within cultured and natural popu lations of the coccolithophore Emiliania huxleyi. The flows of carbon incorporated through photosynthesis were primarily directed towards th e synthesis of lipids (40 to 60%), mainly neutral lipids, whereas rela tive carbon incorporation into proteins was low (ca 20%), regardless o f irradiance levels or growth stage. Actively dividing E. huxleyi cell s showed higher rates of carbon incorporation into protein during dark ness than during the previous light period, whereas under energy-limit ed growth conditions proteins produced during the light period were ca tabolized in darkness. The observed C-14 labelling patterns were consi stent with both the measured biochemical composition of E. huxleyi cel ls growing in cultures under the same conditions and with that of cocc olithophore-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 dy namics of blooming events. Furthermore, the high-lipid, low-protein me tabolism 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 typi cal of blooms of E. huxleyi.