A new computer model reveals how nature captures CO₂ with surprising efficiency – and how we might copy the cleverest tricks to build future technologies that suck carbon from the air and help to curb global warming.
Over billions of years, nature has evolved multiple chemical pathways to transform carbon dioxide (CO₂) into useful molecules such as sugars and proteins.
Scientists have identified seven chemical workflows that living organisms use to convert CO₂ into useful building blocks such as sugars and amino acids.
Photosynthesis is the best-known way to capture CO₂ – but not the most efficient. Microscopic organisms have evolved other chemical pathways that do the same job more rapidly and using less energy.
For the first time, researchers have developed a computer model that can analyse and compare the efficiency of CO₂ fixation across nature’s chemical pathways – and understand why some work better than others.
The model also lets researchers fine-tune chemical steps to find the most efficient way to fix CO₂.
The new insights could pave the way for artificial CO₂ factories: advanced facilities that pull carbon from the air and transform it into useful outputs – from fuels and plastics to green materials – with benefits for both the climate and industry.
“We hope that our research can help to develop systems that extract CO₂ from the air – for example from coal power plants or aluminium factories. But before that can happen, we need to understand exactly how CO₂ is best captured and then test the technology in real plants,” explains a researcher behind the study, Bernhard Palsson, Scientific Director of the Novo Nordisk Foundation Centre for Biosustainability at the Technical University of Denmark in Kongens Lyngby.
Nature’s seven strategies for capturing CO₂
In chemistry, a chemical reaction is efficient if it requires the least amount of energy to get from the substrate to the product and the chemical reaction takes place as rapidly as possible.
Capturing CO₂ and converting it into building blocks like sugar is called fixation – a chemical lock-in that binds the gas into compounds the cell can use.
In the study, the researchers investigated the energy efficiency of two of the seven known metabolic pathways for fixing CO2.
One is the Wood-Ljungdahl signalling pathway, which various bacteria use to convert CO₂ into useful products.
The other is the reductive glycine signalling pathway, which some types of bacteria also use to fix CO₂.
The glycine pathway can be up to 1,000 times more energy-efficient than Wood-Ljungdahl, partly because it uses less of the cell’s energy currency, ATP – and relies on simpler chemical fuel.
Both metabolic pathways are also linear, so the end products differ from the starting materials.
In addition to the two linear pathways, in which the process stops after one pass, there are five cyclic pathways. Here, the end products function as part of the starting material again – just like in a recycling loop in which nothing is wasted. The cycle works like a self-sustaining loop, in which nothing is wasted and energy flows efficiently.
“These are the known metabolic pathways to fix CO₂. There may be more than these, and in the future, we may be able to develop completely new, human-made CO₂ pathways – designed from the ground up to be even more rapid and more energy efficient than nature’s own and may be designed to be even more efficient,” Palsson says.
Small difference – big CO₂ effect
The computer model shows where in the metabolic pathways small differences result in the observed difference in efficiency. These differences stem partly from variation in the structure of the enzymes that drive the reactions.
By comparing the two pathways, researchers can pinpoint exactly what makes one far more efficient than the other. This includes how enzymes – tiny cellular catalysts – direct reactions to minimise energy waste.
The difference is so great that the glycine pathway in the model can be up to 1,000 times more efficient than the Wood-Ljungdahl pathway.
In the second part of the study, the researchers investigated how the physical division of the steps in the metabolic pathways affects the efficiency of overall CO₂ fixation.
Imagine that CO₂ fixation via the two metabolic pathways can take place inside a bacterial cell, in which there is no physical division between the different enzymes and products of the subreactions, or in a eukaryotic cell (animal or plant), in which the interior of the cell is divided into compartments where each step in the metabolic pathways can take place.
The researchers found that the internal compartmentalisation of plant cells – where each process takes place in its own tiny section – boosts CO₂ fixation efficiency. It is like each station in a factory having its own workshop – where every step unfolds without distraction or delay.
From bacteria to the CO₂ factories of the future
Bernhard Palsson says that the insight into nature’s ways of energy-optimising the fixation of CO2 opens the door to creating systems to counteract climate change.
The new model enables researchers to build more precise CO₂ reactors – engineered systems that pull carbon from the air and convert it into valuable products such as fuel, plastics or chemicals.
In their simulations, the researchers found a design that was 10,000 times more efficient than previous experimental systems. This is like trading a water pistol for a pressure washer in pulling CO₂ from the air.
“Our next step will be to do the same studies on the cyclic metabolic pathways for CO2 fixation. The aim is to identify the most promising CO₂ pathway and scale it up in a larger test facility to determine whether the technology can be used in practice,” concludes Bernhard Palsson.
