Engineering a More Efficient System for Harnessing Carbon Dioxide

Autotrophic carbon fixation transforms more than 350 gigatons of CO2 annually.

The Science

To reverse-engineer a biosynthetic pathway for more effective carbon fixation.

  • Conceived several theoretical CO2 fixation routes that (i) start with a carboxylase reaction, (ii) regenerate the carboxylation substrate to allow for continuous cycling, and (iii) feature a dedicated output reaction to channel the fixed carbon into a product.
  • The CETCH cycle was drafted by metabolic retrosynthesis, established with enzymes originating from nine different organisms of all three domains of life, and optimized in several rounds by enzyme engineering and metabolic proofreading. The CETCH cycle adds a seventh, synthetic alternative to the six naturally evolved CO2 fixation pathways, thereby opening the way for in vitro and in vivo applications.

The Impact

  • In the end, through sequencing and synthesis, 17 different enzymes from 9 different organisms across the three kingdoms of life were incorporated.
  • These parts were combined to achieve a proof of principle CO2 fixation pathway performance that exceeds twat can be found in nature.
  • Potential: Synthetic CO2-fixation cycles can be introduced into organisms to bolster natural photosynthesis or, in combination with photovoltaics, lead the way to artificial photosynthesis.


Biological carbon fixation requires several enzymes to turn CO2 into biomass. Although this pathway evolved in plants, algae, and microorganisms over billions of years, many reactions and enzymes could aid in the production of desired chemical products instead of biomass. Researchers constructed an optimized synthetic carbon fixation pathway in vitro by using 17 enzymes—including three engineered enzymes—from nine different organisms across all three domains of life. The pathway is up to five times more efficient than the in vivo rates of the most common natural carbon fixation pathway. Further optimization of this and other metabolic pathways by using similar approaches may lead to a host of biotechnological applications.


Schwander, T., L. Schada von Borzyskowski, S. Burgener, N. Socorro Cortina, and T. J. Erb. 2016. “A Synthetic Pathway for the Fixation of Carbon Dioxide in vitro,Science 354(6314), 900–4. DOI:10.1126/science.aah5237.