Biochemical composition and growth of the marine microalga Dunaliella tertiolecta (Butcher) with different ammonium nitrogen concentrations as chloride, sulphate, nitrate and carbonate.

Abstract

Cultures of the marine microalga Dunaliella tertiolecta were grown in ammonium chloride, sulphate, nitrate and carbonate at concentrations ranging from 0.25 to 16 mg.atom N/l. Cells were harvested in the stationary phase and cell density and biochemical composition determined. Biomass production at the end of the stationary phase, expressed as cell density, was affected by the concentration of ammonium-N in the medium but not by the ammonium compound used. Optimal growth conditions for obtaining maximum cell density, between 1.86×106 and 2.81×106 cells/ml, were 2, 4 and 8 mg.atom N/l. The compound and concentration of ammonium-N had little effect on the growth velocity of D. tertiolecta cultures in the logarithmic phase, with values of 0.35±0.06 doublings/day under all the conditions assayed. The ammonium compound and the concentration of nitrogen affected the concentration of different cellular constituents such as protein, carbohydrate, lipid and chlorophyll a, although these changes were not necessarily related to cell density in the culture. Protein, the most affected fraction, tended to increase with an increase in the nitrogen concentration for all the ammonium compounds used. Maximum protein/ml was obtained with ammonium carbonate at all the nitrogen concentrations used. Maximum protein/cell occurred at the higher nitrogen concentrations (16 and 32 mg/atom N/l) for all the ammonium compounds. Considering the optimum growth interval (2-8 mg.atom N/l), maximum protein/cell concentrations were also obtained in the cultures with ammonium carbonate. Carbohydrate and lipid concentrations varied less than protein concentration. Maximum values of carbohydrate/ml were also found in the ammonium carbonate cultures. Maximum lipid/cell concentrations occurred at the lowest nitrogen concentrations, in contrast to protein values. As a percentage of the total organic matter, protein increased and lipid decreased with the nitrogen concentration, whereas carbohydrate remained constant. Consequently, lipid seemed to be the storage product in this marine microalga. Gross energy values in the different cultures were a function of nitrogen concentration, maximum differences occurring in the ammonium carbonate cultures. The biochemicalvariability of this microalga must have a marked effect on its value as a source of single-cell protein, as chemicals or as feed in mariculture