Can algae help us feed the world?

Supercharging conversion of carbon dioxide to sugars could dramatically improve crop yields.

A pyrenoid (blue) is seen in a cross-section of an algal cell by false-coloured electron microscopy. The pyrenoid sits inside the chloroplast (green), which harvests light energy to drive carbon fixation.
Algae may hold the key to greater plant efficiency, allowing us to grow more food, faster and with less water and fertiliser.

Researchers have identified a protein in algae that helps it take in carbon dioxide from the air and process it with remarkable efficiency.

The team, led by Carnegie Institution for Science's Martin Jonikas, published the work in Proceedings of the National Academy of Sciences.

All photosynthesis uses the enzyme Rubisco to convert atmospheric carbon dioxide into carbon-based sugars, such as glucose and sucrose. In fact, nearly all the carbon that makes up living organisms was at some point "fixed" from the atmosphere by this Rubisco.

Plants – including crops – are limited in how fast they can grow by the rate of this reaction. Much research has been focused on ways to speed this up to increase crop yields (see Super rice for a hungry planet).

Rubisco is so efficient that it changed our atmosphere, but may at the same time have become a victim of its own success.

"Rubisco functioned very efficiently in the ancient Earth's carbon dioxide-rich environment," Jonikas said.

"But it eventually sucked most of the CO2 out of the atmosphere, to the point where CO2 is a trace gas today."

At current concentrations of carbon dioxide at around 0.04% of molecules in today's atmosphere, Rubisco works extremely slowly. However, algae have evolved a way to make Rubisco run faster – turbo-charging the reaction rate.

It has developed a tiny compartment in the cell called the pyrenoid where carbon dioxide is concentrated around Rubisco to make it run faster.

So the research team looked at how and why Rubisco clusters in the pyrenoid.

Jonikas and his team found it was affected by a protein they called EPYC1 (Essential Pyrenoid Component 1). EPYC1 bound to Rubisco and packaged it into the proteins in the pyrenoid's interior.

"A lot of additional work is needed to fully understand EPYC1 and pyrenoids, but our findings are a first step toward engineering algal carbon-capture efficiency into crops," Jonikas said.

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Bill Condie is head of publishing at The Royal Institution of Australia and former publisher of Cosmos.
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