Microbubble enhanced CO2-to-ethanol conversion for artificial CC condensation pathways.

Developing minimized artificial pathways for upcycling CO2 into renewable biofuels is significant for improving carbon conversion efficiency. Here, we designed and demonstrated two linear and short artificial CO2-to-ethanol (CTE 2.1 and 2.2) pathways based on carbon-carbon (CC) bonding enzymes such as glycolaldehyde synthase (GALS) and phosphoketolase (PKT). Notably, PKT-mediated CTE 2.2 pathway comprised only six reaction steps, which was shorter than GALS-mediated CTE 2.1 pathway, enabling one step coupling of CCPi bonds. This artificial CTE 2.2 pathway was further optimized by discovering and screening PKT with high formaldehyde condensation activity, along with enhancing CO2 solubility through microbubble aeration. With the optimized CTE 2.2 pathway, an ethanol yield of 1.029 mM at a carbon conversion rate of 33.5 nmol/mg·min was obtained, outperforming the reported artificial pathways for upcycling CO2. The carbon-conserved and ATP-independent CO2-to-ethanol system provides a carbon-neutral avenue from CO2 to other biofuels in the context of sustainable development.