Chemical composition of the coccolithophorid Emiliania huxleyi under light-limited steady state growth

Changes in the chemical composition of the coccolithophorid Emiliania huxleyi as a function of growth rate were examined on cells maintained in continuous cultures. The cellular content of particulate organic (POC) and inorganic carbon (PIC) increased with growth rate. The PIC/POC and the POC/Chlorophyll-a (Chl.-a) ratios did not show any distinct variation with growth rate. The organic composition of E. huxleyi was characterized by the presence of large amounts of lipids (45-60% of POC) and comparatively low protein-C cell quotas (25-30% of POC). The relative contribution of lipid-C to POC increased linearly with growth rate whereas those of protein-C and carbohydrate-C showed an opposite trend. The percentage of lipid-C relative to total cellular organic carbon increased as a function of total carbon cell quota. The patterns of carbon incorporation into photosynthetic end products were consistent with the measured biochemical composition. The rates of dissolved carbon release were low, representing 1-4% of the total carbon incorporation. The significance of these results for the understanding of E. huxleyi bloom dynamics is discussed.