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Nature’s Recyclers - Graphics

Plastic-eating bacteria could revolutionize recycling

Five big ideas shaping the biotech revolution

A new front is opening in the war on waste, but can it scale?

In France, biotech startup Carbios recycles polyethylene terephthalate (PET), a strong and lightweight plastic that’s used to make drinks bottles, food trays, and textiles. But instead of grinding it down or using chemicals, it mixes the PET with a bacterial enzyme that chews it up. It’s a pioneering process—and it might just offer a glimpse of the future. 

Carbios is commercializing an idea that has steadily been gaining traction in biochemistry research: Enlisting microbes to eat plastic, breaking it down for reuse. And as we look to minimize global carbon emissions, this experimental approach could prove invaluable. 

“This offers a way to remake new plastics without having to go back and dig out more fossil fuels to make fresh ones,” says Dr. Elizabeth Bell, who works on the discovery and optimization of enzymes for the recycling of plastics at the US government’s National Renewable Energy Laboratory. 

Plastic is a popular material because it is cheap and versatile. We produce around 450 million tonnes of it each year, but this has a deleterious impact on the environment because it’s mostly made from petrochemicals. It is often thrown away after a single use, so we also produce around 400 million tonnes of plastic waste each year. 

Huge quantities of this waste are incinerated, releasing the carbon into the atmosphere, and what escapes the incinerators accumulates in landfills and the natural environment. At least 14 million tons of plastic end up in the ocean every year, according to a report by the International Union for Conservation of Nature. Another influential report anticipates that, by weight, there will be more plastic than fish in the sea by 2050.

Nature’s Recyclers - Graphics

To reduce plastic’s environmental impact we must find ways to do more with the plastic that’s already out there. Conventional methods of recycling cause it to degrade, so eventually new plastic has to be made from virgin materials. 

To recycle plastic indefinitely, you have to break it down into its fundamental building blocks, called monomers. But the chemical reaction to do this doesn’t work very well unless the stream of plastic is pure. Problem is, most plastic waste is a mixture of different types. 

That’s where enzymatic recycling comes in. The field has exploded since 2016, when a team of Japanese scientists published a paper about a bacteria that could metabolize PET using an enzyme that we now call IsPETase. 

The process appeals because it works under mild conditions and requires no noxious chemicals. It also means that the PET may not need to be separated out from other types of plastic, since enzymes are specific. 

“What the enzyme could potentially do is chemically sort out the PET from the mixed waste sample, without you having to do any manual sorting,” says Bell. 

Enzymatic recycling is potentially lucrative. Annual demand for common types of plastic is expected to grow by 90 percent to 403 million metric tons by 2050. Over that same timeframe, Carbios—which has raised €71.8 million in funding—expects advanced recycled PET to grow into a €200 billion market.

The discovery of IsPETase has kickstarted a search for other plastic-eating bacteria as part of a broader trend of looking for organisms for commercial applications known as bioprospecting. Microbe hunters go to a place where they might find a bacterium capable of breaking down a target plastic, and starve it of all types of food other than the plastic they want to see it metabolize. If it survives, they know it has eaten the plastic; then they must isolate the enzyme that has enabled this to happen. 

This process takes a long time. The bacteria discovered by the Japanese group remains the single documented case of any microbe that can use PET plastic as a sole food and energy source. Others do it as a side-function but, currently, they’re all too slow to have a meaningful impact on global plastic waste.

Scientists, then, must improve them by tinkering with bacterial DNA. Bell has used genetic engineering to optimize IsPETase to work faster, but believes we will inevitably discover new enzymes altogether. “Enzymatic recycling is still in its infancy for many other types of plastic,” she says. 

Within a decade, enzymatic recycling of PET is likely to become more commonplace, she predicts, and other plastics will follow. The technique uses equipment that has already been proven for large operations, which means it has the capacity to scale up. In 2025, Carbios plans to open its first commercial plant, which it claims will recycle 50,000 tonnes of PET waste per year. 

This potential shift in recycling technology could open up a variety of new possibilities.

In theory, if this new technology becomes mainstream, each city could have its own semi-automated recycling plant. The monomers would feed directly into a nearby processing facility and the plastics would be passed on to local industries. 

What’s more, enzymatic recycling may eventually help clear up our oceans. In 2019, scientists genetically engineered marine algae to produce and secrete IsPETase, enabling it to break down plastic in saltwater. Bell explains that this could possibly be industrialized via a sewage plant-like system; ocean plastic would be collected and put into a controlled reactor with the engineered algae. She notes that one wouldn’t want to release genetically modified organisms into the oceans without knowing exactly what they might do. 

And, if we wanted to eliminate certain plastics altogether, we may be able to engineer microorganisms that consume the products of enzymatic recycling. “So you can break down the plastic into monomers, then another organism can come along and basically eat those monomers as food,” says Bell.

However, it’s unlikely that all kinds of plastic can be efficiently digested. In some cases, such as polyethylene, their chemical bonds will be too strong for the enzymes to overcome. It’s also expensive, though Bell is confident that costs will come down as the technology matures. 

And then there are the possible legal hurdles because of the risks of genetically modified plastic-eating bacteria escaping into the environment. In Bell’s view, however, the risk is minimal because large-scale reactions such as Carbios’ are being done using the enzyme alone, and the engineered microbes from which the enzyme is harvested wouldn’t work outside of a controlled laboratory environment. 

“The risks of industrial plastic-degrading bacteria escaping into the environment are very low,” says Bell. “Scientists work hard to develop fail-safe mechanisms to ensure these bacteria can’t survive on their own in the wild.”

Ultimately, it is likely that the global plastic problem will call for a diverse mix of technological solutions—as well as ratcheting up the drive to simply use less of it. “But enzymatic recycling is filling an important gap.”

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