Bioconversion of C1 and C2 artificial photosynthesis products into high-value bioproducts by mixotrophic microalgae Chlorella pyrenoidosa

This study investigated the use of C1 and C2 products synthesized through artificial photosynthesis to enhance the growth and synthesis of pigments, starches, and lipids of Chlorella pyrenoidosa. Compared with the control group, potassium acetate and ethanol significantly promoted the growth of microalgae, while methanol and potassium formate showed certain inhibitory effects on the growth of microalgae, indicating that C2 products were more conducive to the growth of microalgae. It is worth noting that the ability of microalgae to utilize potassium formate after domestication was significantly enhanced, indicating that domestication treatment of microalgae is an effective means to improve the utilization rate of C1 products. Both C1 and C2 products significantly promoted the accumulation of lipid and starch in microalgae cells, and C2 products significantly increased the lipid and starch yield of microalgae, with potassium acetate being the most effective. Under the treatment of 5 g/L potassium acetate, biomass productivity of C. pyrenoidosa reached 0.28 g/L d(-1), while starch and lipid yield reached 17.2 mg/L d(-1) and 25.2 mg/L d(-1), respectively. Transcriptomic analysis revealed significant upregulation of genes involved in photosynthesis, energy metabolism and other elated pathways under the influence of different organics. Furthermore, the addition of potassium acetate and formate reduced the dependency of microalgae on photosynthesis, while ethanol and potassium acetate significantly accelerated the energy metabolism of microalgae, establishing the basis for microalgae growth and biomass production. In conclusion, potassium acetate was found to be a relatively suitable product of artificial photosynthesis for enhancing the production of high-value bioproducts by mixotrophic microalgae, and when C1 products were used for microalgae culture, pretreatment such as microalgae domestication was particularly important.