Changes in protein, carbohydrates and gross energy in the marine microalga Dunaliella tertiolecta (Butcher) by nitrogen concentrations as nitrate, nitrite and urea

Abstract

Cultures of the marine microalga Dunaliella tertiolecta were grown in nitrate, nitrite and urea at concentrations ranging from 0·25 to 16 mg atom. N/litre. Great biochemical variability has been shown in this microalga as a function of high nitrogen concentrations for all the sources used. Cellular protein and carbohydrates and gross energy per ml of culture increased proportionally to the increase in the N concentration, under conditions that maintain constant the N P ratio. Two kinds of cultures are defined: low nitrogen cultures <2 mg atom. N/litre, and high nitrogen cultures > 2 mg atom. N/litre. Variability mainly appears in the second type of cultures. Protein/cell values of up to 4·94, 5·47 and 1·41 times higher have been observed in nitrate, nitrite and urea cultures, respectively, when comparing protein/cell values obtained in high N cultures with those obtained in low N cultures. Similar variations have been observed in the carbohydrates/cell content, with values up to 3·16, 3·30 and 1·77 times higher in the high than in the low N cultures. Biochemical variability is greater in nitrate and nitrite cultures (inorganic sources of nitrogen) than in urea cultures (organic source of N). Lipid/carbohydrates ratio seems to be a convenient parameter for characterizing the physiological state of a microalgal population. This biochemical variability must have a marked effect on the value of this microalga as a source of single cell protein, chemicals or as feed in mariculture.