Influence of phosphorus and silicon on lipia class production by the marine diatom Chaetoceros gracilis grown in turbidostat cage cultures

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.