Production of intracellular and extracellular lipid classes by Chaetoceros gracilis was studied over a wide range of supply rates of inorganic phosphorus and silicon. The cage culture turbidostat, a continuous culture technique providing closely controlled nutrient concentrations and population densities, was used for growing the diatom. Nutrient, intracellular lipid and chlorophyll a analyses were performed over the whole range of nutrients used, but dissolved lipid production was measured only at the extremes of the ranges of nutrient concentrations. The production of triglycerides, a storage class of lipids, was triggered by nutrient stress with either phosphorus or silicon, as had earlier been demonstrated with nitrogen. The synthesis of phospholipids was reduced under phosphorus stress, while the synthesis of chlorophyll a was increased by silicon stress. The increase in chlorophyll a per cell under silicon stress brings into question the use of this pigment as a measure of biomass. Particulate lipid y e l d was highest in intermediate concentrations of both nutrients.

The green algae D. tertiolecta, the flagellate I. galbana and the diatom C. gracilis were grown in batch cultures. The organisms were analysed for lipid class composition at the logarithmic and stationary growth phases using the Chromarod-Iatroscan thin layer chromatography with flame ionization detection (TLC-FID) system.There were major differences in lipid class production among the organisms investigated, but few differences in lipid class distribution between log phase and stationary phase cultures of D. tertiolecta and I. galbana. C. gracilis displayed the general trend exhibited in diatom metabolism, which can be characterized by an increase in triacylglycerol synthesis in situations of stress.