High-starch algae are important in biofuel production, as a feed supplement in agriculture and as an efficient way to bind carbon dioxide. Researchers have now found a new method to control starch storage in algae - a finding with potential applications in areas such reducing greenhouse gases.

“Modifying a blue light-activated signalling pathway makes it possible to regulate storage. This offers a significantly higher yield than traditional methods that rely on nutrient deprivation,” says Dimitris Petroutsos, Associate Professor at Uppsala University, who led the study recently published in Nature Communications.

Light is essential for photosynthetic organisms such as plants and algae. In green algae, such as Chlamydomonas reinhardtii, the energy from sunlight is used to convert carbon dioxide (CO₂) into carbohydrates, which can be used for growth or stored as energy in the form of starch.

Special effect of blue light

In the new study, researchers show that blue light has a special effect. It affects starch storage in algae through a protein called phototropin. When phototropin senses blue light, it activates a signalling pathway that reduces starch accumulation by controlling key metabolic genes. This light-driven regulation of carbon storage allows algae to fine-tune their energy allocation between immediate growth (low starch) and long-term storage (high starch).
The researchers found that genetically modified algae without phototropin increased starch content from 5 to 25 per cent of the dry weight of the algae – without compromising growth or photosynthesis.

Could reduce greenhouse gases

Three areas that could benefit most from greater regulation of starch storage are:

• Biofuels: Starch-rich algae can be used to produce bioethanol and other biofuels. Manipulating phototropin signalling makes it possible to increase starch production in a controlled manner.
• Sustainable agriculture: Microalgae are used as a feed supplement in agriculture. Controlling starch storage would make it possible to improve the nutritional value of the supplements and make them more efficient as animal feed and soil enhancers.
• Carbon capture: By controlling starch accumulation, we can influence how algae store carbon, which could help capture carbon dioxide and reduce greenhouse gases.

“Previous studies have mostly focused on how nutrient deficiency affects starch formation, but in this study we have been able to show that blocking the phototropin pathway makes it possible to increase starch storage without affecting growth,” says Petroutsos.