New discovery reveals how diatoms capture CO2 so effectively

Tiny diatoms in the ocean are masters at capturing carbon dioxide (CO₂) from the environment. They fix up to 20 percent of the Earth’s CO₂. A research team at the University of Basel, Switzerland, has now discovered a protein shell in these algae that is necessary for efficient CO₂ fixation. This groundbreaking discovery can provide ideas for bioengineering approaches to reduce CO₂ in the atmosphere.

Diatoms are too small to see with the naked eye, yet they are one of the most productive algae species in the ocean and play an important role in the global carbon cycle. Using photosynthesis, they absorb large amounts of CO₂ from the environment and convert it into nutrients that feed much of the life in the ocean. Despite their importance, it has remained largely unknown how diatoms carry out this process so efficiently.

Researchers led by Prof. Ben Engel at the Biozentrum of the University of Basel together with researchers at the University of York, UK, and the Kwansei-Gakuin University in Japan have now discovered a protein shell that plays a key role in the diatoms' CO₂ fixation. Using cutting-edge imaging technologies such as cryo-electron tomography (cryo-ET), the researchers were able to reveal the molecular architecture of the so-called PyShell protein sheath and decipher its function. The results of the studies have now been published in two articles in "Cell".

PyShell crucial for efficient CO₂ fixation

In plants and algae, photosynthesis takes place in chloroplasts. Inside these chloroplasts, energy from sunlight is harvested by thylakoid membranes and then used to help the enzyme Rubisco fix CO₂.

However, algae have an advantage: they pack all their Rubisco into small compartments called pyrenoids, where CO₂ can be captured more efficiently. “We have now discovered that diatom pyrenoids are encased in a lattice-like protein shell,” says Dr. Manon Demulder, author on both studies. “The PyShell not only gives the pyrenoid its shape, but it helps create a high CO₂ concentration in this compartment. This enables Rubisco to efficiently fix CO₂ from the ocean and convert it into nutrients.”

When the researchers removed the PyShell from the algae, their ability to fix CO₂ was significantly impaired. Photosynthesis and cell growth were reduced. “This showed us how important the PyShell is for efficient carbon capture – a process that is crucial for ocean life and the global climate,” says Manon Demulder.

Bioengineering for CO₂ reduction?

The discovery of the PyShell could also open promising avenues for biotechnological research aimed at combatting climate change – one of the most pressing challenges of our time. “First of all, we humans must reduce our CO₂ emissions to slow the pace of climate change. This requires immediate action,” says Ben Engel.

“The CO₂ that we emit now will remain in our atmosphere for thousands of years. We hope that discoveries such as the PyShell can help inspire new biotechnology applications that improve photosynthesis and capture more CO₂ from the atmosphere. These are long-term goals, but given the irreversibility of CO₂ emissions, it is important that we perform basic research now to create more opportunities for future carbon-capture innovations.”

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