Boosting Photosynthesis For Carbon Capture

Using light to break down and bind CO₂: two new research groups want to make what nature already does much more efficient

To the point

• CO₂ reduction: Two new research groups at the Max Planck Society are working on a more efficient form of photosynthesis to break down and bind CO₂ using sunlight.
• Innovative methods: The first research approach uses computational protein design and directed evolution to develop artificial enzymes that optimise photosynthesis. The second approach focuses on adapted cyanobacteria that store more CO₂ in their cells.
• Carbon capture and utilisation: In addition to storing CO₂, the groups also aim to use the carbon captured for sustainable products - an important component of a circular economy in the chemical industry.

On 1 July 2025, the Max Planck Society will launch two new research groups that aim to make the core of photosynthesis significantly more efficient. With the help of sunlight, CO₂ will be broken down into its components and fixed. The research is still in its early stages. However, if scaling proves successful, large amounts of atmospheric CO₂ could potentially be captured. Still, there's long way to go. And the two research group leaders and biochemists Adrian Bunzel and Andreas Küffner are aware that today's carbon capture solutions are too expensive and inefficient, and that the risks associated with underground storage or injection are, in some cases, impossible to assess. Nevertheless, capturing carbon from the atmosphere will remain necessary for decades to come, especially since emissions from sectors like chemicals and cement cannot be completely eliminated. It is therefore better to close the current research gaps today rather than tomorrow.

'Nature is conservative'

Adrian Bunzel was already researching so-called photoactive enzymes for biological photovoltaics as an early career-research group leader at ETH Zurich. Enzymes are nature's catalysts and accelerate biochemical reactions. His photoenzymes generate electricity using sunlight. At the Max Planck Institute for Terrestrial Microbiology, Bunzel is now targeting new enzymes that, like plants, use the energy of sunlight to break down CO₂ molecules into their individual components and bind them. In nature, however, photosynthesis only binds about one percent of the theoretically available carbon in biomass due to very complex reaction pathways. "Nature is conservative", says Tobias Erb, Director at the Max Planck Institute for Terrestrial Microbiology. With photosynthesis, it has established a sufficient but inefficient way of breaking down CO₂ using sunlight.

In his research, Adrian Bunzel aims to produce artificial photoenzymes that greatly simplify natural photosynthesis and significantly boost its efficiency.. He is relying on two cutting-edge methods: computational protein design (- the computer-aided development of new proteins - and directed evolution, a technique that mimics natural evolution in the lab to optimise enzymes through mutation and selection.

Both methods have been awarded the Nobel Prize in recent years. "It's like learning to fly", says Erb. "We observed how birds fly and studied lift. Then we built airplanes, but without wings. They don't look like birds, but they do what they are supposed to do and, in some respects, even better, more specifically, and more efficiently." For Adrian Bunzel, this opens the door to entirely new possibilities: This is precision bioengineering. It's no longer about how we manipulate biology, but what we want to design," he says. The new possibilities in protein design allow us to ask: Which proteins add value, for example, in achieving sustainability goals?

Better bacteria for photosynthesis

Andreas Küffner will increase the efficiency of photosynthesis at the Max Planck Institute for Multidisciplinary Sciences in a completely different way. He ensures that more CO₂ accumulates in the organelles of plant cells as a starting material than is usual in nature. Andreas Küffner developed and demonstrated the concept during his postdoc in Tobias Erb's laboratory in vitro - which means in a test tube. After all, the more CO₂ that's available, the more can be used. The concept also helps to circumvent a fundamental limitation of nature, which fixes significantly less CO₂ in cells with an enzyme. Küffner focuses on cyanobacteria, which are bacteria with the ability to photosynthesise. "Organelles in bacteria are like small reactors. They are there to capture and concentrate CO₂", he explains. And cyanobacteria have another advantage: they grow easily and quickly and are relatively easy to genetically manipulate. "We could also work with algae, but they are more difficult genetically", says Küffner. Both algae and cyanobacteria can perform photosynthesis, and both can be scaled up in specialised processes. Looking ahead, some people might envision multi-storey greenhouses with Plexiglas cylinders containing shimmering green streaks. That could work well for algae. But cyanobacteria thrive best in open waters or shallow pools. Many people are familiar with the sight of thick, bright green, shimmering blooms from the Baltic Sea, for example. The disadvantage in the wild is that the bacteria extract oxygen from the water. So would artificial pools be conceivable? "My research is not aimed at scaling", says Küffner. Instead, he is tackling another issue: cyanobacteria require nitrogen and phosphorus to thrive, and producing these fertilizers consumes significant resources, while also generating CO₂.

A long way to go before application

What connects the two research groups is photosynthesis. "Light is everywhere; it's one of the most sustainable energy sources there is", says Tobias Erb. Otherwise, both groups are pursuing their own goals. While Andreas Küffner works with and on cells, Adrian Bunzels begins by testing his photoenzymes 'in vitro', i.e. in a test tube, before incorporating them 'in vivo' into the metabolism of a real organism for photosynthesis. "It can easily take more than ten years from enzyme idea to plant", says Tobias Erb. Much can happen along the way, which is a hallmark of basic research. "If something doesn't work, that has value, too. If you don't try, you'll never know if it could have worked," says Küffner. In order to conduct the best possible research in this field today - and contribute to a more liveable future tomorrow - the Max Planck Society is pursuing two entirely new lines of research with Andreas Küffner and Adrian Bunzel.

Storing and using carbon

The basic problem is well known: Germany emitted around 600 million tonnes of CO₂ in 2023, and globally over 40 gigatonnes (billion tonnes) of this greenhouse gas are still released into the atmosphere every year - directly leading to global warming. "Assuming we wanted to remove up to 40 gigatonnes of CO₂ from the air each year, no single technological concept could achieve this. And it doesn't have to, because the solution will ultimately be a mix of different strategies," says Bunzel. This always includes preventing emissions from being produced in the first place. And what if 90 percent of emissions were avoided in the future? "According to predictions, we would still have to actively capture three to five gigatonnes of CO₂",says Tobias Erb.

The only large-scale technical facility for capturing CO₂ directly from the ambient air is currently located in Iceland. There is still heated debate about whether and to what extent such technologies should be used in global decarbonisation. While they offer clear benefits, technical capture processes also pose challenges, especially when it comes to storing CO₂ safely. Hence the abbreviation CSS for carbon capture and storage. And the filter plant in Iceland is prohibitively expensive: each tonne of filtered CO₂ costs over 1,000 euros to remove. In addition to capturing and storing CO₂, for example directly at emission sources, the carbon obtained can be also be reused. Chemically incorporating it into plastics or other materials that are needed in everyday life is called carbon capture and utilization (CCU). Andreas Küffner and Adrian Bunzel are pursuing both goals. "By incorporating CO₂ into the biological metabolism, we can use it to produce virtually any chemical that can be made biologically," says Adrian Bunzel. Possible products include biofuels or raw materials for the chemical industry that are produced sustainably. Once carbon capture and utilisation is operating efficiently, it will be an important component of a circular economy in the chemical industry.

BEU