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Plastic-Eating Bacteria Turn Waste Into Useful Materials

A recycling bin with the triangle recycling logo on the front.
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Researchers have engineered a strain of E. coli that can digest polyethylene terephthalate (PET) plastics and transform them into adipic acid – a useful feedstock for nylon materials, drugs and fragrances.

Published in ACS Central Science, the study reports the use of this E. coli strain to break down common plastic bottles and other plastic waste.

Tackling the global plastic problem

Each day, the equivalent of 2,000 garbage trucks worth of plastic is dumped into our oceans and rivers. Recycling initiatives can go some way towards tackling the growing problem of plastic waste, as products can be shredded, melted and molded into new products, but novel methods for dealing with this waste are still needed.

Previously, researchers at the University of Edinburgh reported having successfully engineered a strain of E. coli that could convert the central component found in plastic bottles – terephthalic acid – into the more valuable and sought-after compound vanillin, which is responsible for vanilla’s distinctive taste.

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Now, another group of University of Edinburgh researchers, again led by Professor Stephen Wallace report having successfully expanded E. coli’s biosynthetic pathways to have it metabolize terephthalic acid into adipic acid, a common feedstock compound that is ordinarily generated from fossil fuels in a very energy-intensive process.

“We use a technique called synthetic biology, where we insert new pieces of DNA into E. coli that program the cell to perform new chemical reactions,” said Wallace, a professor of chemical biotechnology at the University of Edinburgh. “Here we programmed bacteria to made adipic acid from plastic waste [which] now enables nylon for clothing to be made from a waste plastic bottle.”

E. coli turns plastic waste into a valuable feedstock

The newly engineered E. coli strain works by producing enzymes that can transform terephthalic acid into shorter-chain acids, such as muconic acid and adipic acid. To complete the conversion of muconic acid into adipic acid, the researchers used a second type of E. coli – which produces hydrogen gas – and a palladium catalyst.

The researchers found that attaching the engineered E. coli strains to alginate hydrogel beads helped to improve their efficiency. From their experiments, they determined that up to 79% of the terephthalic acid could be converted into adipic acid using this first-of-its-kind one-pot bio-upcycling pathway.

Having confirmed that this transformation was possible, the researchers then tested the hydrogel-supported E. coli strains on two real-world samples: PET bottles and industrial plastic waste.

“We applied these strains to both a plastic bottle we found on the street and a sample of plastic waste generated by a local industrial company in Scotland, and they both worked remarkably well,” Wallace said. “This demonstrates to us how plastic waste can serve as a new feedstock for chemical production and we’re currently applying this finding to a range of different industrial products.”

As the researchers say in their paper, the development of sustainable bio-based methods for plastic recycling is an “elegant approach to creating a circular chemicals economy.” Their new method proceeds at room temperature, at an ambient pH and within 24 hours, making it well suited to wider adoption.

“We are currently working intensely with a number of industrial partners in the UK and beyond to intensify this process so that we can make real-world clothing fibers from plastic waste,” Wallace said. “This is also just the beginning of what I think we can do – so watch this space!”

Reference: Valenzuela-Ortega M, Suitor JT, White MFM, Hinchcliffe T, Wallace S. Microbial upcycling of waste PET to adipic acid. ACS Cent Sci. 2023. doi: 10.1021/acscentsci.3c00414

Professor Stephen Wallace was speaking to Alexander Beadle, Science Writer for Technology Networks.