Changes in the nutrient composition of Tetraselmis suecica cultured semicontinuously with different nutrient concentrations and renewal rates

The marine microalga Tetraselmis suecica was cultured semicontinuously with two nutrient concentrations: 2 and 4 mmol N l −1 and five rates of daily renewal of the culture media in the range 10–50%, in order to study the changes in the nutrient composition of the cells produced under such conditions. An increase in the renewal rate produced an increase in protein and lipid content of the biomass to the detriment of carbohydrate content, the only fraction accumulated by T. suecica as energetic reserve under nitrogen deficient conditions. Cellular content of these three fractions did not accurately reflect the relative composition, since total organic content of the cells decreased with increasing renewal rates attenuating the increase in protein and lipid contents. As a result, cell caloric content remained almost constant. The degree of unsaturation of fatty acids increased with increasing renewal rate, with a two-fold increase of the percentage of total n − 3 fatty acids. On the other hand, the percentage of eicosapentaenoic acid (EPA) decreased with increasing renewal rate indicating a different control of the metabolism of this long-chain polyunsaturated fatty acid in T. suecica. Results demonstrate the efficiency of the use of the semicontinuous culture technique for the production of microalgal biomass of optimal biochemical composition being especially useful for the study of the nutritional requirements of filter-feeding marine organisms.