Engineered system harnesses carbon dioxide faster than plants

A natural process gets an upgrade.

Plants remove carbon dioxide from the air by converting it into organic compounds like sugar. They are just a little too slow. In a new Science study, researchers have developed a synthetic pathway that can do it faster. The pathway uses a new group of CO2-converting enzymes that is nearly 20 times faster than the most prevalent enzyme in nature. It is yet to be implemented in living organisms but could one day be transplanted into plants so they can convert carbon dioxide faster and with less energy.

Tobias Erb, a terrestrial microbiologist at the Max Planck Institute, and colleagues brought together 17 enzymatic compounds from nine organisms in an engineered pathway that converts carbon dioxide into useful organic compounds. We spoke with him about the study.

ResearchGate: What motivated this study?

Tobias Erb: We have taken our inspiration from nature itself. In the last couple of years, we discovered many new mechanisms and pathways for CO2-fixation, the process of converting carbon dioxide to organic compounds, mainly in microorganisms. This means that nature generally has the potential to come up with new CO2-fixation biology. Although nature is apparently very good at tinkering new solutions together, she is not necessarily a great engineer. All of these naturally existing solutions are the product of an evolutionary process, and not rational design. This means that natural pathways all come with certain flaws and disadvantages. So we started to ask if we could create options that would be more efficient than the naturally evolved ones. For instance, plants convert CO2 relatively slowly.

RG: What did you develop?

Erb: We created a designer pathway for CO2-fixation, the CETCH cycle, that is more efficient than naturally existing CO2-fixation pathways. When provided with energy in the reaction tube, this designer pathway is able to continuously fix atmospheric CO2. So we’ve demonstrated that it is possible to rationally design new pathways for CO2-fixiation by following basic chemical rules, and that such pathways can be optimized by including biological design principles.

RG: What was the most challenging aspect of the study?

Erb: The design of the theoretical pathways was very simple. It took us only one to two weeks, or one creative night, to come up with promising synthetic routes. However, finding and bringing all the biological parts together was a tough business. It took us more than two years to screen, test and engineer about five dozen enzymes and variants to identify the final set of seventeen enzymes that we used to construct the CETCH cycle.

RG: How would this be made to work in plants?

Erb: Thus far, our artificial CO2-fixation cycle is a proof-of-principle. It is a “metabolic heart” in a reaction tube. The transplantation of such a “new metabolic heart” into living organisms, such as algae or plants is another big challenge. We cannot predict for sure how such an artificial cycle would perform in the complex background of a plant and if it would indeed be able to fix CO2 faster. Our theoretical calculations suggest that the CETCH cycle could allow plants and other photosynthetic organisms to fix more CO2 with the same amount of light energy, which could lead to higher growth yields. But again, this needs to be tested.

RG: Once it is equipped in plants would the process then happen naturally in the offspring of these plants?

Erb: Of course, the transplantation and implementation in algae and plants would require genetic modifications for the natural offspring of these transgenic organisms to also carry the new process. However, this also means that we would be able to further improve synthetic CO2-fixation pathways by applying evolutionary pressure. In other words, the natural mechanisms of biology can be used to further shape and improve artificial CO2-fixation.

RG: Could this advancement be used to stop the net increase in global carbon dioxide?

Erb: Our primary goal is not necessarily to fight global warming. We are rather interested in engineering biology to convert atmospheric CO2 into useful products. We want to understand the fundamental principles that allow us to convert CO2 into any desirable biochemical compound. This is something that chemistry still cannot do. On a broader perspective, it might be fair to compare our efforts to the developments in chemistry a hundred years ago, when analytical chemistry became synthetic, providing us with completely novel materials, pharmaceuticals etc. This transition from an analytical to a synthetic science has changed the world we live in. The same can happen with synthetic biology and synthetic metabolism that we are trying to achieve in the laboratory.

RG: What other applications does this have?

Erb: Potential host organisms could range from bacteria to algae, and eventually even plants. An interesting feature of the CETCH cycle is that it is designed to feature mainly steps involving chemical reduction reactions. This means that we could eventually directly channel electrons generated from sunlight, hydrogen, or even electricity to CO2-fixation. We see potential for hybrid systems that would combine photovoltaics with organisms containing our CETCH cycle, similar to what has become known as “artificial leaves”.

RG: When do hope to have this implemented in plants?

Erb: The transplantation into plants is of course still a far-fetched goal. It seems more realistic to first equip microorganisms, like bacteria and algae with our synthetic CO2-fixation cycles. With this we could create new ways to synthesize building blocks for the chemical industry.

Featured image courtesy of flickr.