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April 14, 2017

Better together: harnessing cooperating microorganisms to make biodegradable plastic from sunlight

Michigan State University scientists are proposing a new way to economically produce “green” plastics with sunlight and help from cyanobacteria – tiny photosynthetic workhorses, also known as blue-green algae.

The team, led by Taylor Weiss, a post-doctoral student at the MSU-DOE Plant Research Laboratory, took cyanobacteria, that use sunlight to naturally produce sugar, and genetically tweaked them to constantly leak that sugar into a surrounding saltwater medium.

They matched them with natural bioplastic-producing bacteria that fed on the leaked sugar, and the pairing was prolific. The results, published in the current issue of eLife, showed that processed biomass contained a near constant 30 percent bioplastic content, four times more than similar experimental systems. Production rates were more than 20 times faster.

The approach avoids fossil fuels for production and aims to reduce plastic’s impact on the environment. A major problem is that most synthetic plastic is not completely biodegradable, so it lasts for hundreds of years after being discarded, in landfills and in water ecosystems.

Although researchers have developed 100 percent biodegradable plastics made with special bacteria, it is prohibitively expensive.

These methods also tend to rely on feeding plastic-producing bacteria with loads of sugar derived from agricultural crops, like corn or beets that also feed people and animals. So, we risk competing for limited agricultural resources and driving food prices up in the long term.

That’s why scientists are looking to genetically alter cyanobacteria to funnel their outputs into useful products.

“In the case of plastics, cyanobacteria are exceptional at photosynthesis, not at making loads of bioplastic. And current methods where cyanobacteria do it all are inefficient,” Weiss said. “In designing a system that produces the bioplastic in an assembly-line fashion, where each member is strong in its own department, we resulted in a consortium superior to the best cyanobacteria working alone.”

Scientists create gradually more efficient bio-production systems all the time. But a major twist is that his improves over time, without human meddling, Weis said.

“The cyanobacteria constantly make sugar through photosynthesis, and the bacteria constantly beef up on it, which encourages the cyanobacteria to keep producing,” he said. “So, the system continuously evolves in a virtuous cycle.”

Looking forward, Weiss wants to partner cyanobacteria with other specialist bacteria to create cheap, environmentally friendly bioproducts like biofuels to power jets and cars, fragrances, edible dyes and medicines.

“Ultimately, we aren’t just creating alternatives to synthetic products; we’re trying to ask nature to do what it does best­ – figure out the problem for us.”

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