Over 14 million tons of plastic litter ends up in the ocean every year, killing thousands of animals and birds that ingest it. Much of it ends up amassing in giant garbage patches and over time breaking down into smaller microscopic pieces that are harmful to marine life.
A new study offers a glimmer of hope in addressing this marine plastic pollution problem. Researchers at North Carolina State University report in the AIChE Journal that they have genetically engineered a marine microorganism to break down a commonly used plastic in salt water.
Polyethylene terephthalate (PET) is a type of plastic used to make bottles, food packaging and clothes. Much PET plastic waste does not get recycled, and ends up in landfills and aquatic environments. It eventually breaks down into microplastics—particles with a size of less than 5 mm—which are challenging to collect and have been shown to move quickly between aquatic, terrestrial, and atmospheric environments, the researchers point out in the paper.
Some microbes have been found to have the ability to break down plastic. Researchers have genetically engineered bacteria, or even just the enzymes they produce, to convert plastic waste into valuable chemicals. A key limitation with these previously modified organisms is that “their growth is inhibited by high concentrations of salt,” the NCSU team writes. That means microplastics would have to be collected and washed off using large quantities of water before they can be broken down.
So the researchers took a different approach, harnessing two different species of bacteria. The first, Vibrio natriegens, lives in saltwater and reproduces very quickly, doubling in number in under 10 minutes in ideal conditions. The second bacteria, Ideonella sakaiensis, produces enzymes that can deconstruct PET.
The team isolated the DNA sequence from I. sakaiensis that is responsible for producing the enzyme, and inserted it into V. natriegens. The modified V. natriegens could produce the PET-degrading enzymes on the surface of their cells. They found that V. natriegens was able to break down PET into its building blocks in a saltwater environment at room temperature.
“From a practical standpoint, this is the first genetically engineered organism that we know of that is capable of breaking down PET microplastics in saltwater,” said Tianyu Li, a PhD student and the paper’s first author, in a press release. “That’s important, because it is not economically feasible to remove plastics from the ocean and rinse high concentration salts off before beginning any processes related to breaking the plastic down.”
There is still significant work to be done, the researchers say. They now plan to modify V. natriegens so that it can feed on the byproducts it creates when it breaks apart PET, and so it can produce useful chemical molecules in the end.
Source: Tianyu Li, Stefano Menegatti, Nathan Crook. Breakdown of polyethylene therepthalate microplastics under saltwater conditions using engineered Vibrio natriegens. AIChE Journal, 2023.