Optimization of a Chlorella–Saccharomyces co–culture system for enhanced metabolite productivity

Microalgae and yeast co–culture systems are gaining interest as a promising method for higher production of biomass and metabolites. However, because these organisms have particular cultivation requirements, optimization of culture conditions is needed for suitable growth and productivity of the co–culture. This work examines the effects of cultivation media macronutrient composition on the growth and metabolite production of co–cultures of either Chlorella vulgaris or Chlorella sorokiniana with a strain of Saccharomyces cerevisiae. Specifically, the consequence of glucose, yeast extract and peptone supplementation on the physiological responses of the co–culture system was investigated. The co–culture responses were equivalent for both Chlorella species, although C. sorokiniana could maintain a more stable population ratio with yeast. The addition of glucose with peptone significantly enhanced biomass production of the co–culture by approximately 2–fold in comparison to microalgae or yeast monocultures, while the addition of glucose alone or in combination with yeast extract did not exhibit the same effect. An approximately 3–fold increase in lipid content was observed in the co–culture samples under glucose–only supplementation, where yeast growth was restricted. The addition of glucose and yeast extract enhanced the growth of yeast monocultures, but this did not benefit the co–culture. Fourier transform infrared spectroscopy analysis revealed different metabolic fingerprints of the monoculture and the co–culture samples grown in glucose and peptone containing medium, which indicated higher abundance of metabolites including lipids, proteins, carbohydrates in the co–culture samples. Specifically, total protein yields in the co–cultures were increased by 1.6– to 1.7–fold in comparison to microalgae monoculture while total lipid yields were increased by 3.6– to 5.1–fold in the co–cultures. This work highlights the importance of organic carbon and nitrogen availability for microalgae–yeast co–culture growth and their potential for a wide range of valuable applications including nutritional and bioenergy uses.