Improvement of cell growth in green algae Chlamydomonas reinhardtii through co-cultivation with yeast Saccharomyces cerevisiae

Biological fixation methods have attracted considerable attention because they can be applied for the fixation of dilute CO2 in the atmosphere. Co-cultivation of certain microalgae with heterotrophic microorganisms can increase the growth potential of microalgae under dilute CO2 conditions. The objective of this study was to determine the culture conditions under which the growth potential of green algae Chlamydomonas reinhardtii is enhanced by co-culturing with the yeast Saccharomyces cerevisiae, and to identify the cause of the enhanced growth potential using transcriptome analysis. When C. reinhardtii and S. cerevisiae were co-cultured with an initial green algae to yeast inoculum ratio of 1:3, the cell concentration of C. reinhardtii reached 133 x 105 cells/mL on day 18 of culture, which was 1.5 times higher than that of the monoculture. Transcriptome analysis revealed that the expression levels of 363 green algae and 815 yeast genes were altered through co-cultivation. These include genes responsible for ammonium transport and CO2 enrichment mechanism in green algae and the genes responsible for glycolysis and stress responses in yeast. In conclusion, we identified the culture condition suitable for the co-cultivation of C. reinhardtii and S. cerevisiae. In addition, we discuss the cause of the increased growth potential of C. reinhardtii based on transcriptome analysis data. Although further studies are needed to elucidate the full impact of microbial interactions in C. reinhardtii and S. cerevisiae co-cultures, the findings of this study represent an important first step toward achieving this goal.