Comparison of Microalgae Biomass and Lipid Content During Growth in Acorn-Glucose and Low Cost Carbon Sources Under Various Conditions

Background: When organic carbon in mixotrophic cultures used, can also reduce the amount of carbon dioxide in the culture and cost of agitation to facilitate the growth of algal species. Despite the significantly higher biomass and lipid production compared to autotrophic growth, the cost of an external carbon source is expensive than other added nutrients. If low-cost carbon source could use in mass biomass production, the cost of lipid production may be significantly reduced. Objective: The growth of the algae strains Chlorella vulgaris, Botryococcus braunii and Scenedesmus sp. under various conditions in the presence of different carbon sources, including glycerol, acetate, and acorn-glucose, was evaluated to increase the algal biomass and oil content. Methods: Microalgae were cultured in a 300 mL conical flask containing 100 mL of JM, and 10 mL of microalgae was added. In mixotrophic and heterotrophic cultures, 2% sterile carbon sources were added to the sterilized JM medium. Results: The highest biomass concentrations for C. vulgaris, Scenedesmus sp. and B. braunii were obtained in media containing acorn-glucose in heterotrophic conditions; the biomass concentrations for these species were 57.55 %, 66.38 %, and 68.11 % higher, respectively, than for autotrophic growth. The maximum biomass production was 0.16-0.20 g/L·day with glycerol, 0.13-0.16 g/L·day with acetate and 0.18-0.21 g/L·day with acorn-glucose in mixo- and heterotrophic conditions. The highest TAG contents were 15.43 %, 15.24 %, and 16.41 % for C. vulgaris, Scenedesmus sp. and B. braunii, respectively, with acorn-glucose in heterotrophic conditions. Conclusion: The microalgae strains had a high biomass when grown on carbon sources compared to autotrophic growth. Acorn-glucose in heterotrophic conditions yielded the highest biomass. The maximum biomass productivity and specific growth rates were achieved with acorn-glucose>glycerol > acetate and heterotrophic > mixotrophic > autotrophic culture. Heterotrophic conditions with acorn-glucose improved both microalgae growth and triacylglycerol (TAG) accumulation. The fatty acid profiles of the cultures met the necessary requirements and are promising resources for biofuel production.