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March 28, 2018

Light affects cyanobacteria’s diet

Michigan State University scientists have found a link between how water-dwelling bacteria, called cyanobacteria, monitor light quality in their surroundings and how much energy they get out of photosynthesis.

Cyanobacteria are microorganisms – each 25 times smaller than the width of a human hair – that dominate the planet’s oceans, lakes and rivers.

They were one of the first organisms that evolved the ability to photosynthesize billions of years ago, and they have developed countless internal systems to monitor surrounding light quality to fine-tune photosynthesis for optimal performance.

In the study, graduate student Brandon Rohnke and a team from the Beronda Montgomery laboratory show that altering one of those monitoring systems by removing a light-detection protein, RcaE, causes the cyanobacterium, Fremyella, to produce more numerous, but smaller photosynthetic factories that make its food.

The monitoring system, complementary chromatic acclimation, allows cyanobacteria to track light quality – as they sink and float in water – so they tune into and capture the most available wavelength at any time. For example, surface water is rich in red light while deeper levels have abundant green light and scarcer red light.

“In nature, a Fremyella cell has two to three carboxysomes per cell cross-section,” said Rohnke, who works at the MSU-DOE Plant Research Laboratory. “However, lab cells that have had the light-detection protein removed have up to seven carboxysomes, but they are smaller on average.”

The study is part of a long-term project, funded by the Department of Energy, to harness carboxysomes for human uses. Researchers want to refurbish these factories with customized internal machinery that produces biofuels or medical products.

“Somehow, light cues tightly control carboxysome amount and structure, but we still have to figure out how that works,” Rohnke said. “Acquiring that knowledge and gaining the ability to artificially dial the number and size of custom carboxysomes could help us manage productivity levels in future biotech contexts.”

“But before we imagine powering our cars and planes with ‘cyanobacteria fuel,’ we have many other monitoring systems left to decipher. We are slowly and surely getting there," Rohnke said.

The study is published in the journal mSphere.

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