EFFECTS OF INITIAL NITROGEN SUPPLY ON THE GROWTH, MORPHOLOGY AND LIPID ACCUMULATION OF OLEAGINOUS MICROALGA EUSTIGMATOS VISCHERI (EUSTIGMATOPHYCEAE)

This research aimed at analysing the effects of initial nitrogen supply on the growth, morphology and lipids accumulation of an oleaginous microalga of Eustigmatophyceae, Eustigmatos vischeri. E. vischeri was grown in modified BG-11 medium containing four different initial concentrations of sodium nitrate (17.6 mmol/L, 11.7 mmol/L, 5.9 mmol/L and 3.0 mmol/L). The cell morphology and oil droplets formation process of E. vischeri were observed under microscope. It was found that the vegetative cells of E. vischeri were spherical unicellular with smooth cell wall and containing a lobed chloroplast, a red pigment body and many vibrating ganules in cytoplasm. The main reproduction way is by forming autospore such as binary or quadripartition division. With the prolongation of cultivation time, the oil droplets formed gradually under nitrogen depletion. Then, the oil droplets became larger and mutual fusion into larger and larger oil bodies, eventually occupied the main part of the cell. Moreover, the color of cultures changed from green to yellow-green, finally to orange-yellow. The physiological results showed that the highest biomass concentration was occurred at the initial sodium nitrate concentration of 17.6 mmol/L, up to 9.14 g/L. The contents of total lipid (TLs), neutral lipids (NLs) and total fatty acids (TFAs) increased following the reduction of nitrogen concentration. Their maximum contents reached to 60.81%, 56.59% and 53.47% at the basis of dry cell weight, respectively. However, the highest volumetric productivity of TLs, NLs and TFAs were up to 0.24, 0.21 and 0.20 g/(Ld) at 5.9 mmol/L of sodium nitrate, respectively. In addition, the main components of fatty acid were palmic acid, palmitoleic acid, oleic acid and eicosapentaenoic acid, among them, the content of palmitoleic acid was highest one. As a whole, E. vischeri was an oleaginous microalga, suitable for the production of biodiesel and high value-adding of long-chain polyunsaturated fatty acid EPA.