High rates of lipid biosynthesis in cultured, mesocosm and coastal populations of the cocco-lithophore Emiliama huxleyi

The patterns of carbon incorporation into proteins, polysacchandes, l i p ~d s and low molecular weight metabohtes and the resulting cellular biochemical coinposition were examined within cultured and natural populations of the coccolithophore Ernlhanla h u x l e y ~ The flows of carbon incorporated through photosynthesis were pnmanly directed towards the synthesis of liplds (40 to 60%) malnly neutral Ilpids, whereas relatlve carbon incorporation into proteins was low (ca 20 X ) , regaldless of irradiance levels or growth stage Actively dlviding E huxleyi cells showed higher rates of carbon Incorporation into protein dunng darkness than durlng the previous light period whereas under energyhmlted growth condlt~ons protelns produced dunng the light penod were catabolized in darkness The observed I4C labelling patterns were consistent with both the measured blochemical composition of E huxleyi cells growlng In cultures under the same conditions and with that of coccolithophoredominated natural phytoplankton assemblages The relative decrease in cellular d e n s ~t y caused by a lipld-nch composition could be signlf~cant for the buoyancy of cells and, consequently, for the dynamics of blooming events Furthermore, the hlgh-lipid, low-proteln metabolism charactenstlc of this species implies an increase of carbon uptake relatlve 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