Process for symbiotic culture of Saccharomyces cerevisiae and Chlorella vulgaris for in situ CO₂ mitigation

Abstract

Industrial biotechnology relies heavily on fermentation processes that release considerable amounts of CO₂. Apart from the fact that this CO₂ represents a considerable part of the organic substrate, it has a negative impact on the environment. Microalgae cultures have been suggested as potential means of capturing the CO₂ with further applications in high-value compounds production or directly for feed applications. We developed a sustainable process based on a mixed co-dominant culture of Saccharomyces cerevisiae and Chlorella vulgaris where the CO₂ production and utilization controlled the microbial ecology of the culture. By mixing yeast and microalga in the same culture, the CO₂ is produced in dissolved form and is available to the microalga avoiding degassing and dissolution phenomena. With this process, the CO₂ production and utilization rates were balanced and a mutual symbiosis between the yeast and the microalga was set up in the culture. In this study, the reutilization of CO₂ and growth of C. vulgaris was demonstrated. The two organism populations were balanced at approximately 20 × 10⁶ cells ml⁻¹ and almost all the CO₂ produced by yeast was reutilized by microalga within 168 h of culture. The C. vulgaris inoculum preparation played a key role in establishing co-dominance of the two organisms. Other key factors in establishing symbiosis were the inoculum ratio of the two organisms and the growth medium design. A new method allowed the independent enumeration of each organism in a mixed culture. This study could provide a basis for the development of green processes of low environmental impact.