Aerial-Phase Culture Conditions for Biodiesel Production by the Microalga Chlorella vulgaris

The microalga Chlorella vulgaris was cultured under the aerial-phase conditions with or without nitrogen to investigate the effects on lipid production. Under the three culture conditions (liquid conditions without nitrogen; aerial-phase conditions with and without nitrogen), oxygen production decreased during the culture period, indicating that photosynthetic activity was suppressed. The carbohydrate content was lower in the algal cells cultured under aerial-phase conditions than under non-aerial conditions, suggesting that carbohydrate biosynthesis was suppressed and that accumulated carbohydrates were used for lipid biosynthesis. The dry cell weight under aerial-phase conditions with or without a nitrogen source increased 2.9- and 2.4-fold over 14 days, respectively, while lipid content increased 5.1- and 5.9-fold. C. vulgaris underwent cell division and produced biomass and lipids under both nutrient-depleted and nitrogen-supplemented conditions. Aerial-phase cultivation with nitrogen could simultaneously achieve growth and lipid accumulation, supporting the potential for sustainable biodiesel production using C. vulgaris under the aerial-phase conditions.