In order to improve the microalgae lipid productivity and optimize its cultivation conditions, Isochrysis zhanjiangensis was used as the research object, effects of trophic modes, light intensity, and NaNO3 concentration on the growth and lipid accumulation, as well as the relationship between nitrogen consumption and growth in the course of culture were explored. The results showed that microalgae consumed more nitrogen while it grew faster. Compared to photoautotrophic and photoheterotrophic cultivation, more nitrogen was consumed to meet the growth needs under mixotrophic cultivation condition. More protein were accumulated under the conditions of sufficient nitrogen and mixotrophic cultivation, whereas more oil accumulated under the conditions of low nitrogen concentration and light intensity. Although the highest oil content of 46% was obtained under the photoheterotrophic cultivation when the light intensity was 100 μmol/(m2·s) and NaNO3 concentration was 75 mg/L, the biomass concentration was only 0.46 g/L under the same condition. The highest biomass concentration of 2.20 g/L was obtained under the mixotrophic cultivation when the light intensity was 100 μmol/(m2·s) and NaNO3 concentration was 750 mg/L. However, the oil content was only 32.77%. Considering factors, such as lipid productivity and cost-saving, the best lipid productivity of 80.06 mg/(L·d) was obtained under the mixotrophic cultivation when the light intensity was 100 μmol/(m2·s) and NaNO3 concentration was 375 mg/L. Moreover, polyunsaturated fatty acids accounted for 30.82% of the total fatty acids contents under this condition. Therefore, this is a suitable condition for I. zhanjiangensis to produce microalgae oil as a nutritional substitute.
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