5-19: Exploring mixotrophic cultivation of the microalga C. sorokiniana as a promising feedstock production strategy for biofuel production

Microalgae have the potential to provide large amounts of lipid-containing biomass as renewable oil feedstock for biofuel production. Mixotrophic algal culture makes it possible to enhance photoautotrophic growth with additional organic carbon and energy sources. We evaluated mixotrophic growth potential of C. sorokiniana supplemented with different concentrations of glucose (0-10 g/L). The results suggested that the mixotrophic growth was not a simple combination of the photoautotrophic and mixotrophic growth. The photosynthetic reactions and the related enzymes were assessed to elucidate mixotrophic capacities of the algae. Under mixotrophic growth condition, the specific growth rate and biomass production were notably enhanced in comparison with photoautotrophic or heterotrophic cultures individually or combined. The specific growth rate and biomass concentration with 4 g/L initial glucose in mixotrophic culture were 2.67 /day and 3.55 g/L, respectively, which were respectively 1.64 /day and 1.46 g/L in the corresponding heterotrophic culture, and were respectively 0.45 /day and 0.47 g/L in photoautotrophic culture. Particularly, unlike in most green algae, the lipid contents were approximately 3- and 6-folds respectively higher compared with heterotrophic and photoautotrophic cultured algae, with C16-C18 (~95%) fatty acid as the main lipid composition. These findings support mixotrophic culture as an efficient microalgal cultivation method with the characteristics of high growth rate, high biomass yield and high lipid content.