Scientists Work to Make Better Plastics From Sunlight

By combining two kinds of bacteria and sunlight, researchers have devised a new way to efficiently create biodegradable plastics.

One of the bacteria, Halomonas boliviensis, exists naturally in reflective, salty Bolivian pools a few thousand meters above sea level. Its partner, synthetic cyanobacteria, produces sugar by using sunlight. H. boliviensis then feeds on the sugar to produce the polymer used to create bioplastics, which the bacteria stores similar to how humans store fats. 

“We know these symbioses exist in nature already,” said Taylor L. Weiss, the lead author of the most recent study, who has been working for months with Daniel Ducat and Eric Young at Michigan State University. “We’re mimicking that.”

Compared to similar experimental systems, the bioplastic production rates from the paired bacteria were more than 20 times faster. Some research has attempted to carry out this process using one species, rather than two. The more widespread approach to creating bioplastics and other bioproducts require corn and sugar (to feed the bacteria). And producing corn and sugar require hundreds of acres of farmland, which could otherwise be used for human food production.

“While that process is renewable, it means you're also using farmland that you would be using for crops or food,” said Ducat, assistant professor at MSU’s biochemistry and molecular biology department. “And it creates some environmental questions.”

The new process is similar, but the source of sugar—the cyanobacteria and sunlight—is less expensive and resource-intensive. Additionally, this system doesn’t require fertile land or clean water at all, said Ducat.

RTS1C5ZA Plastic bottles are sorted to be recycled at Cedar Environmental waste management company in Beit Mery, Lebanon August 17, 2017. Reuters

“You have basically a one pot of efficient conversion of sunlight to sugar and then in that same pot, conversion of the sugar to any variety of downstream products,” said Ducat. 

The next step is scaling up from a laboratory to saltwater ponds of plastic-and-sugar-producing bacteria. Maintaining productivity and stability while avoiding contamination are a few goals.

“Optimizing in a flask is not the goal. The real test is moving outside,” said Weiss. “Moving to a larger scale is the next test.”

RTR4SP6T Workers load collected plastic bottles on to a truck at a junk shop in the Philippines March 10, 2015. Reuters

But the scientists are optimistic.

Within their study, they did not have to use antibiotics to prevent contamination in the samples, and when there was contamination, the mighty Bolivian bacteria beat out the competition.

"Halomonas is fighting to keep them out. It occupied the niche," said Weiss. "That’s huge."

This study aimed to produce bioplastics, but different species of bacteria could use the same process to create other bioproducts. The platform is particularly flexible, according to researchers. 

"It's a platform for discovery as well," said Weiss. 

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