Synthetic biology pulls carbon dioxide out of the atmosphere

Although plants have been turning atmospheric carbon dioxide into useful carbon compounds for millions of years, the enzyme used to do this transformation, called rubisco, is both slow and fickle—it fixes oxygen instead of CO₂ about 20% of the time.

So a team of researchers led by Tobias J. Erb at the Max Planck Institute for Terrestrial Microbiology decided to make a synthetic biology system that fixes CO₂ more efficiently than plants.

They started with a CO₂-fixing enzyme from the pink proteo­bacterium named Methylobacterium extorquens. The enzyme, called crotonyl-CoA carboxylase/reductase, is about 20 times as fast at fixing CO₂ as rubisco in plants.

Next the researchers selected a motley crew of 16 additional enzymes from nine other life-forms—including humans, plants, and microorganisms—to run the world’s first CO₂-fixing cycle in a test tube (Science 2016, DOI: 10.1126/science.aah5237).

The final output of the newly crafted cycle, named CETCH, is the two-carbon glyoxylate, which could then be converted to industrial products, such as biofuels or pharmaceuticals.

Increasing CO₂ concentration in the atmosphere is a problem, Erb says. “But at the same time, it is also a carbon source from which we can make useful compounds.”

The energy-efficient CO₂-fixing pathway is a breakthrough for synthetic biology, and it extends “the capabilities for recapturing atmospheric CO₂ for use as a carbon feedstock,” say Fuyu Gong and Yin Li at the Chinese Academy of Sciences in a commentary on the new study (Science 2016, DOI: 10.1126/science.aal1559). However, the next step—transplanting the system into an organism and getting the various enzymes to function optimally—will be a huge challenge, they add.