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NC State researchers engineer 'promising' plastic-degrading microbe to help polluted oceans

A single-use plastic water bottle floats in clear blue water with sand at the bottom. A black chord is wrapped around the mouth of the water bottle.
Brian Yurasits
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Unsplash
A single-use plastic water bottle floats in the waters of the Gili Islands, Indonesia. Plastic water bottles are mainly made from PET and have low recycling rates.

Researchers at North Carolina State University have genetically engineered bacteria to break down a source of plastic pollution in the ocean.

The project, led by NC State PhD candidate Tianyu Li, is the first to ever successfully break down polyethylene terephthalate, or PET plastic, in salt water.

“PET is a really common plastic,” said Li. “In our daily life, the water bottle is made from PET, and we have a lot of clothes made from polyester, which are actually PET as well. During the process of people washing their laundry, there are some microfibers kind of shredded by the washing process. So, the polyethylene as a micro-form are actually more than we can imagine.”

NC State PhD candidate Tianyu Li stands in a white lab coat and blue gloves while handling lab equiptment.
Courtesy of Tianyu Li
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North Carolina State University
NC State PhD candidate Tianyu Li led the project that developed a genetically modified organism to eat PET in salt water. She has spent more than two years working in the Crook Lab bioengineering marine bacteria.

According to the National Renewable Energy Laboratory, more than 82 million metric tons of PET plastics are produced each year, with PET bottles having a low recycling rate of 15-35%.

To help address the pollution problem, researchers engineered an organism that combined features of two different bacteria species. They took DNA from a microbe known to eat PET that did not grow well in salt water, and they put it in Vibrio natriegens, a rapidly reproducing saltwater microbe.

The project’s research paper stated that the resulting organism could completely degrade one gram-per-liter of PET in about 24 years. NC State professor Nathan Crook said that natural degradation of PET varies based on factors like UV exposure, but a water bottle made from PET could take hundreds of years to decompose naturally.

Li and Crook agreed that one of the next steps is to determine how to make the engineered microbe’s degradation process even faster.

“This microbe would need to be about 100-fold faster than it currently is for people to think about using it to do something really useful in the problem,” Crook said. “It's still faster than nature, but it's a long way away from seeing commercial use. But it's a step in the right direction.”

Crook estimated that at least five to 10 more years of research lie ahead to optimize the engineered organism.

“It really depends on if we can get – lucky is not the right word – but engineer our own luck,” Crook said. “We're hoping to essentially throw the kitchen sink at it. Try all the techniques we can to make it work, and we might get lucky.”

In addition to improving degradation speed, Crook said another goal is to have the engineered microbe not only break down PET particles, but to have it convert those broken down remnants into economically desirable molecules or products.

Numerous blobs sit against a gray background. The blobs are irregular shapes, and some are blue, and others are orange. They are up-close images of microplastics.
Courtesy of Tianyu Li
/
North Carolina State University
An up-close image of microplastics that were collected from a shoreline. Li's engineered bacteria can degrade macro and micro forms of PET plastic, but the smaller the plastic particles, the faster the break down can occur.

Project leader Li said that as promising and exciting as the project’s results have been, she knew it could not completely solve the plastic pollution problem, which she described in her research paper as needing multidisciplinary solutions.

“I gradually built some good habits about doing plastic recycling and trying to avoid purchasing as much plastic as I can,” Li said. “This is a really exciting thing. And meanwhile, it kind of raised my awareness about how to save the planet from certain pollutions.”

The project was funded by the National Science Foundation.

Sophie Mallinson is a daily news intern with WUNC for summer 2023. She is a recent graduate from UNC-Chapel Hill, where she studied journalism. Sophie is from Greenville, N.C., but she enjoys the new experiences of the Triangle area. During her time as a Tar Heel, Sophie was a reporter and producer for Carolina Connection, UNC-Chapel Hill’s radio program. She currently is heavily involved in science education at Morehead Planetarium and Science Center.