PETpla.net Insider 09 / 2018

Professor John McGeehan and colleagues inadvertently engineered an enzyme better at degrading plastic than the enzyme which evolved in nature (photo: Stefan Venter, UPIX Photography) Benjamin Luethi inspecting the I23 beamline detector at the Diamond Light Source which played a major role in the discovery (photo: Diamond Light Source) MATERIALS / RECYCLING PET planet Insider Vol. 19 No. 09/18 www.petpla.net 10 A happy accident: PET-eating enzyme performance improved Researchers at the UK’s University of Portsmouth and the National Renewable Energy Laboratory in the USA ‘inadvertently’ engineered an enzyme to be even better at eating plastic than the one originally found in nature. Plastics generally and PET in par- ticular have not been around very long but the impact of discarded, unrecy- cled plastics on the environment has been little short of disastrous. While nature is resilient and resourceful it is quite surprising to find that a life form – specifically, a bacterium – has already developed the ability to eat, digest and convert plastic back to its constituent components. The ability to enzymatically degrade PET had been thought to be limited to a few fungal species, which means that biodegradation has not been seen as a viable remediation or recycling strategy. A team of scientists, from the Kyoto Institute of Technol- ogy and Keio University, Japan, led by Shosuke Yokida, screened naturally- occurring microbial communities in 250 samples of PET debris from sedi- ment, soil, wastewater and activated sludge close to a recycling facility and, in 2016, isolated a novel bacterium, “Ideonella sakaiensis 201-F6”. When grown on PET, this strain produces two enzymes capable of hydrolyzing both PET and its reaction intermedi- ate, mono(2-hydroxyethyl) terephthalic acid, and convert it back into its two environmentally benign monomers: terephthalic acid and ethylene glycol. The microbial colonies degraded PET film at 0.13mg cm –2 day –1 at 30 °C, which is neither fast enough nor on a sufficiently large scale to be commercially viable. While studying the bacterium dis- covered by the Yokida team, Profes- sor John McGeehan at the University of Portsmouth, UK, and Dr Gregg Beckham at NREL, in the USA, solved the crystal structure of PETase - the enzyme that digests PET - and used PETase (PET-digesting enzyme)