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

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.