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Leave it to the market to find a solution not politicians.

‘We are just getting started’: the plastic-eating bacteria that could change the world

https://www.theguardian.com/environment/2023/sep/28/plastic-eating-bacteria-enzyme-recycling-waste

Excerpt:

In 2001, a group of Japanese scientists made a startling discovery at a rubbish dump. In trenches packed with dirt and waste, they found a slimy film of bacteria that had been happily chewing through plastic bottles, toys and other bric-a-brac. As they broke down the trash, the bacteria harvested the carbon in the plastic for energy, which they used to grow, move and divide into even more plastic-hungry bacteria. Even if not in quite the hand-to-mouth-to-stomach way we normally understand it, the bacteria were eating the plastic.

The scientists were led by Kohei Oda, a professor at the Kyoto Institute of Technology. His team was looking for substances that could soften synthetic fabrics, such as polyester, which is made from the same kind of plastic used in most beverage bottles. Oda is a microbiologist, and he believes that whatever scientific problem one faces, microbes have probably already worked out a solution. “I say to people, watch this part of nature very carefully. It often has very good ideas,” Oda told me recently.

.....In the years after their discovery, Oda and his student Kazumi Hiraga, now a professor, continued corresponding and conducting experiments. When they finally published their work in the prestigious journal Science in 2016, it emerged into a world desperate for solutions to the plastic crisis, and it was a blockbuster hit. Oda and his colleagues named the bacterium that they had discovered in the rubbish dump Ideonella sakaiensis – after the city of Sakai, where it was found – and in the paper, they described a specific enzyme that the bacterium was producing, which allowed it to break down polyethylene terephthalate (PET), the most common plastic found in clothing and packaging. The paper was reported widely in the press, and it currently has more than 1,000 scientific citations, placing it in the top 0.1% of all papers.

.....A discovery like Oda’s is only a starting point. To have any hope of mitigating this globe-spanning environmental disaster of our own making, the bacteria will have to work faster and better. When Oda and his group originally tested the bacteria in the lab, they placed them in a tube with a 2cm-long piece of plastic film weighing a 20th of a gram. Left at room temperature, they broke down the tiny bit of plastic into its precursor liquids in about seven weeks. This was very impressive and far too slow to have any meaningful impact on plastic waste at scale.

Fortunately, over the past four decades, scientists have become remarkably proficient at engineering and manipulating enzymes. When it comes to plastic chewing, “the Ideonella enzyme is actually very early in its evolutionary development”, says Andy Pickford, a professor of molecular biophysics at the University of Portsmouth. It is the goal of human scientists to take it the rest of the way.

.....It is often two steps forward, one step back,” says Elizabeth Bell, a researcher at the US government’s National Renewable Energy Laboratory (NREL) in Colorado.

Bell’s own work – which focuses on PETase, the enzyme that Ideonella sakaiensis produces to break down PET plastics – takes a brute-force approach in order to turbocharge natural evolution. Bell takes the regions of the enzyme that work directly on plastic and uses genetic engineering to subject them to every possible mutation. In the wild, a mutation in an enzyme might occur only once in every few thousand times the bacteria divide. Bell ensures she gets hundreds, or thousands of potentially beneficial mutants to test. She then measures each one for its ability to degrade plastic. Any candidates that show even marginal improvement get another round of mutations. The head of the NREL research group, Gregg Beckham, refers to it as “evolving the crap out of an enzyme”. Last year, she published her latest findings, on a PETase enzyme she had engineered that could degrade PET many times faster than the original enzyme.

But building an enzyme that suits our purposes isn’t just a case of scientists tinkering until they get the perfect tool. Before the publication of Oda’s paper in 2016, no one knew that bacteria capable of digesting plastic existed. Now, we have one solidly documented case. Given that we have discovered only a tiny fraction of microbial life, a far better candidate might be out there. In engineering terms, we may currently be trying to squeeze elite racing performance out of a Toyota Yaris engine, when somewhere, yet to be discovered, there is the bacterial equivalent of a Ferrari......

.....In the case of plastic-eating microbes, that leap has now been made. Since 2021, a French company named Carbios has been running an operation that uses a bacterial enzyme to process about 250kg of PET plastic waste every day, breaking it down into its precursor molecules, which can then be made directly into new plastic. It’s not quite composting it back into the earth itself, but Carbios has achieved the holy grail of plastic recycling, bringing it much closer to an infinitely recyclable material like glass or aluminium.

.....In the wild, the bacteria would produce a limited amount of plastic-targeting enzyme, and many other enzymes and waste products as well. To accelerate the process, Carbios pays a biotech company to harvest and concentrate huge amounts of pure plastic-digesting enzyme from bacteria. The Carbios scientists then place the plastic nurdles in a solution of water and enzyme, inside a sealed steel tank several metres high. In the adjoining lab where the process is tested, you can observe the reaction taking place in smaller vessels. Inside, the off-white plastic bits swirl about like the flakes in a snowglobe. As time goes on, the plastic erodes away, its components dissolving into the solution, leaving only a greyish liquid churning behind the glass. The liquid now contains not solid PET, but two liquid chemicals called ethylene glycol and terephthalic acid, which can be separated out and turned into new plastic.

The technique Carbios has developed appears to scale easily. Two years ago the company was recycling a few kilos of plastic in a lab; now it can do about 250kg a day. In 2025, it will open a much bigger facility near the border with Belgium, with the capacity to recycle more than 130 tonnes a day.

.....Will highly evolved microbes really deliver us from the plastic crisis? Some scientists think the technology will remain limited. A recent critical review in the journal Nature noted that many kinds of plastics would probably never be efficiently enzymatically digested, because of the comparatively huge amount of energy required to break their chemical bonds. Andy Pickford, the professor at Portsmouth, is familiar with the limitations, but thinks many good targets still exist. “Nylon is tough but doable,” he says. “Polyurethanes, also doable.” The scientists at Carbios agree, predicting that they will have a process to recycle nylon within a few years. If those predictions come to pass, about a quarter of all plastics would become truly recyclable; if there turns out to be an enzyme match for all the plastics that are theoretically susceptible to being broken down, just under half of all plastic waste could be on the table.

.....Oda is convinced we haven’t even scratched the surface. When he and his colleagues first found Ideonella at the dump nearly 20 years ago, it wasn’t working solo. “As soon as I saw the film of micro-organisms on the plastic, I knew it was many microbes working together,” Oda told me. His team realised that while Ideonella was breaking the plastic into its industrially valuable precursors, other microbes were stepping in to further chew those into simple nutrients the microbial community could use. They were symbiotic. Partners, in a way. Oda has since written several papers pointing out that microbial communities might be developed into a system to remove micro- and nanoplastics from the soil. But he has received little interest.

In our conversations, Oda repeatedly bemoaned the lack of truly world-changing ideas coming from people who wanted to commercialise the discoveries he and his colleagues had made. There was an incredible amount of excitement about a factory that could turn old plastic into new; far less, it seemed, about one that could turn plastic back into water and air.