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The discovery of how a critical enzyme “hidden in nature’s blueprint” works sheds new light on how cells control key processes in carbon fixation, a process fundamental to life on Earth.

The discovery, made by scientists from the Australian National University (ANU) and the University of Newcastle (UoN), could help create climate-resilient crops capable of sucking carbon dioxide from the atmosphere more efficiently, helping to produce more food in the process.

The study, published in Scientific progressdemonstrated a previously unknown function of an enzyme called carboxysomal carbonic anhydrase (CsoSCA), which is found in cyanobacteria — also called blue-green algae — to increase the microorganisms’ ability to extract carbon dioxide from the atmosphere.

Cyanobacteria are known for their toxic blooms in lakes and rivers. But these little blue-green bugs are widespread and live in the world’s oceans as well.

Although they can pose a danger to the environment, researchers describe them as “little carbon superheroes”. Through the process of photosynthesis, they play an important role in sequestering about 12% of the world’s carbon dioxide each year.

The first author and Dr. researcher Sasha Pulsford from ANU describes how remarkably efficient these microorganisms are at sequestering carbon.

“Unlike plants, cyanobacteria have a system called a carbon-concentrating mechanism (CCM) that allows them to fix carbon from the atmosphere and convert it into sugars at a significantly faster rate than standard plants and crop types,” said Mrs Pulsford.

At the heart of the CCM are large protein compartments called carboxysomes. These structures are responsible for releasing carbon dioxide, which houses CsoSCA and another enzyme called Rubisco. The enzymes CsoSCA and Rubisco work in unison, demonstrating the highly efficient nature of CCM. CsoSCA works to create a high local concentration of carbon dioxide inside the carboxysome, which Rubisco can then take up and convert into sugars for the cell to eat.

Lead author Dr Ben Long from the UoN said: ‘Until now, scientists were not sure how the CsoSCA enzyme was controlled. Our study focuses on unraveling this mystery, particularly in a large group of cyanobacteria found around the world. What we found was completely unexpected.

“The CsoSCA enzyme dances to the tune of another molecule called RuBP, which activates it like a switch. Think of photosynthesis as making a sandwich. Carbon dioxide from the air is the stuffing, but the photosynthetic cell must provide the bread. That’s RuBP Just like you need bread to make a sandwich, the rate at which carbon dioxide is converted to sugar depends on how quickly RuBP is supplied.

“How quickly the CsoSCA enzyme delivers carbon dioxide to Rubisco depends on how much RuBP is present. When there is enough, the enzyme turns on. But if the cell runs out of RuBP, the enzyme shuts down, making the system highly tuned, and surprisingly, the CsoSCA enzyme has been built into nature’s blueprint all along, waiting to be discovered.”

Scientists say engineering crops that are more efficient at capturing and using carbon dioxide will provide a huge boost to the agriculture industry by significantly improving crop yields while reducing demand for nitrogen fertilizers and irrigation systems. It will also ensure that the world’s food systems are more resilient to climate change.

Ms Pulsford said: “Understanding how CCM works not only enriches our knowledge of the natural processes that are fundamental to Earth’s biogeochemistry, but can also guide us in creating sustainable solutions to some of our biggest environmental challenges , which the world faces.”