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

Purpose: CO fixation methods using green algae have attracted considerable attention because they can be applied for the fixation of dilute CO in the atmosphere. However, green algae generally exhibit low CO fixation efficiency under atmospheric conditions. Therefore, it is a challenge to improve the CO fixation efficiency of green algae under atmospheric conditions. Co-cultivation of certain microalgae with heterotrophic microorganisms can increase the growth potential of microalgae under atmospheric 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.

Results: 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 × 10 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 included genes responsible for ammonium transport and CO enrichment mechanism in green algae and the genes responsible for glycolysis and stress responses in yeast.

Conclusion: We successfully increased C. reinhardtii growth potential by co-culturing it with S. cerevisiae. The main reasons for this are likely to be an increase in inorganic nitrogen available to green algae via yeast metabolism and an increase in energy available for green algae growth instead of CO enrichment.