Bio-mitigation of CO2: The co-production of phycocyanin and optically pure (R)-γ-valerolactone with perfect enantiomeric excess.

To overcome the climate crisis, various greenhouse gas (GHG) mitigation strategies have been developed, and every effort has been made to achieve carbon neutrality. Given that petroleum-based industries and the transportation sector emit enormous amounts of GHGs, the product spectra of biorefineries should be expanded beyond drop-in biofuels to include more value-added products. This study aimed to construct a CO2 mitigation system. When CO2 was used as the sole feedstock, value-added phycocyanin and enantioselective γ-valerolactone (GVL) were produced as follows (i) Galdieria sulphuraria was phototrophically cultured to produce phycocyanin (ii) the residual G. sulphuraria after phycocyanin extraction was used as the feedstock for producing levulinic acid and formic acid and (iii) the engineered hydroxybutyrate dehydrogenase-based chemo-enzymatic reaction converted levulinic acid to (R)-GVL with perfect enantiomeric excess > 99.999 %. The results not only contribute to broadening the product spectrum of CO2 biorefineries but also provide strategies to achieve carbon neutrality.