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 rare 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.