Hundreds of millions of metric tons of plastic are created and discarded every year. The vast majority are petroleum-based, and they do not naturally degrade. Unless plastic is recycled, and very few are, it can remain a waste item for up to a thousand years. But what if we could find an organism that literally eats plastic?
“We screened several bacterial strains to see if they could use the polyurethane as a food source,” said Jon Pokorski, professor of nanoengineering at UC San Diego.
Pokorski said they found two kinds of bacteria that could use polyurethane as an exclusive food source. This form of plastic goes by the acronym TPU, for thermoplastic polyurethane, and it’s used for lots of things from cushions and shoes to watchbands.
Pokorski said the U.S. produces over a million tons of polyurethane a year.
Plastic that carries the seeds of its degradation
Pokorski and his team embedded bacterial spores in the plastic as it was created. Spores are like dormant seeds that will become bacteria. When the spores wake up, they start feasting on the TPU.
So what wakes them up?
“They need something wet and they need things like sugar,” Pokorski said.
“Things that happen in soil. Things that you find in compost. So one of the things that’s really neat about these is we think that it doesn’t really matter what environment they’re disposed in. If they go to a landfill the bacteria will wake up and degrade the polymers. If they go to compost, same thing.”
The TPU plastic that researchers used in their experiment can degrade on its own, at least partially. Some scientists in the field say the UCSD team may have shown a way to jump-start the biodegradation process, but they did not make it happen.
Pokorski argues the jump-start is considerable.
“We found that if you take the TPU that is sold commercially and you put it into compost. Some portion of it degrades, about 50% or so,” he said. “When we took the TPU that had the bacterial spores in them and put it in the compost, you’re going to see the plastic disintegrate. And over the course of five months about 95% of the plastic has disintegrated to nothing.”
Making product work for industry
The way researchers talk about the business of adding spores to the manufacture of polyurethane sounds no different from adding salt to your soup. UCSD bioengineer Adam Feist, another member of the research team, said when you make plastic the spores are just another additive.
“When you make rubber compounds, plastic compounds, it’s a mixture of things. It’s the raw polymer itself. It’s colorants and other things that get poured in there, right? The spores actually in this case are just one more thing that gets poured into the mix,” Feist said.
One of UCSD's partners in the research project was the chemical company, BASF. A paper on the research project was published in the journal Nature Communications
Feist said the bacteria they used for the experiment was modified in the lab by speeding up their evolution so they could select bacteria that could withstand the high heat of plastic manufacturing. The bacteria doesn’t degrade all plastics, only the TPU selected by researchers.
Feist calls their plastic material a contrived marriage between microbes and polymers. We’ll find out if that shotgun wedding can lead to the use of a common plastic that doesn’t become a solid waste nightmare.
