Bacteria found to eat PET plastics could help do the recycling. 

Millions of tonnes of PET plastic are manufactured every year, most ending up as waste

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Nature has beaten us to it again. It has taken just 70 years for evolution to throw up a bacterium capable of breaking down and consuming PET, one of the world’s most problematic plastic pollutants.

Japanese researchers discovered and named the species, Ideonella sakaiensis , by analysing microbes living on debris of PET (polyethylene terephthalate) plastics they collected from soil and wastewater.

The bacterium seems to feed exclusively on PET and breaks it down using just two enzymes. It must have evolved the capability to do this because the plastics were only invented in the 1940s.

The team hopes the discovery will lead to new ways of breaking down

plastic, using either the bacteria themselves, or the two enzymes they use for the job.

New ways of breaking down PET are sorely needed – vast quantities of discards clog up landfill sites and

natural environments around the world. In 2013, 56 million tonnes of PET were manufactured – about a quarter of all plastics produced that year – but only 2.2 million tonnes were recycled, the team says.

“Large quantities of PET have accumulated in environments across the globe,” says Kohei Oda of Kyoto Institute of Technology in Japan, whose team made the discovery. “So, to solve this problem, microbes that break it down could be useful.”

Slow and steady

So how do the bacteria do it? They link to the PET with tendril-like threads. They then use two enzymes sequentially to break down PET into terephthalic acid and ethylene glycol, the two substances from which it is manufactured and that are not harmful to the environment.

The bacteria then digest both substances. This could mean they would be useful for getting rid of polluting plastics in the environment.

Their ability to reconstitute the starting materials also lends them to recycling strategies. But the process takes a long time – about 6 weeks at 30°C to fully degrade a thumb-nail-sized piece of PET.

“We have to improve the bacterium to make it more powerful, and genetic engineering might be applicable here,” says Oda, whose team is already experimenting with this.

One way of speeding things up would be to transfer the genes that make the two enzymes into a faster growing bacterium like Escherichia coli , says

Uwe Bornscheuer of Greifswald University in Germany.

Given that E.coli secretes the first breakdown product -terephthalic acid – instead of consuming it, this would also make it more practical prospect for recycling, he says.

Bornscheuer says it’s encouraging that nature has evolved a natural consumer of PET, just 70 years after the plastic began accumulating in the environment. So far, only a few fungal species have been reported to biodegrade PET.

“I’m sure we’ll find more microbes in nature that have evolved to degrade other plastics,” he says. “It’s just a matter of searching properly and having patience like the Japanese group to narrow the search down to a single bacterium.”