Utilization of glucose and acetate by Chlorella and the effect of multiple factors on cell composition

Microalgae are rich in various high-value compounds and thus have been proposed for use in biodiesel production and other industrial processes. Mixotrophy of microalgae can generate a high biomass and a high cell content of desirable compounds. To elucidate the probable relationship between pH drift, carbon source utilization, light intensity, and biomass accumulation in Chlorella cultivation, we compared the growth, pH drift, total biomass, and lipid and starch contents of Chlorella sorokiniana GXNN01 under different culture conditions. We also labeled the cell with C-13-labeled substrates. The results of pH drift and C-13 labeling showed that Chlorella preferred acetate under high light, but glucose under low light. Glucose utilization resulted in decrease of pH, while acetate had the opposite effect. A combination of acetic acid and glucose as carbon source maintained the pH close to the initial value and significantly increased total biomass production. Cultures using acetic acid as carbon source or addition of sodium acetate under low light appeared to enhance total lipid content, while pH adjustment, addition of two carbon sources, or addition of sodium acetate under normal light (20 mu mol photons m(-2) s(-1)) resulted in high starch content. This knowledge will guide future Chlorella cultivation.