Autotrophic Biodiesel Production from the Thermotolerant Microalga Chlorella sorokiniana by Enhancing the Carbon Availability with Temperature Adjustment

Chlorella sorokiniana is a thermo-resistant microalga that is widely used for production of biofuel such as biodiesel. When cultured at 37°C under autotrophic conditions, C. sorokiniana showed the highest production of biomass, whereas the cells exhibited the highest production of fatty acids at 30°C. Herein, culture temperature shift was applied to improve autotrophic biodiesel production via the two-stage strategy. In addition, in order to increase biomass production, dissolved inorganic carbon source (mainly bicarbonate ion species), which is essential for photosynthesis, was supplied in the cultures by dissolving the CO₂ in alkaline solution. As a result, cell growth increased up to 22% compared to that of the control cells by supplying constant inorganic carbon source into the cultures. The cells cultured under the condition of temperature shift (37°C to 30°C) and bicarbonate solution showed an increase in biodiesel productivity by 31% when compared to the cells that were cultured without such temperature adjustment (37°C to 37°C). In brief, our temperature shift method with bicarbonate buffer system (inorganic carbon supply) will improve biofuel production including biodiesel from C. sorokiniana under autotrophic conditions.