PLASTIC EATERS
5. Read the text and complete the statements below. Then, use them to report the case study to the class.
PET is used to make most plastic drinks bottles and many synthetic fibres. It decomposes very slowly and accumulates in animals’ stomachs, and so may enter the human food chain.
In 2016, Japanese researchers reported that the bacterium Ideonella sakaiensis had evolved the ability to use two enzymes – PETase and MHETase – to break down PET plastic into terephthalic acid and ethylene glycol, which it digests and uses as sources of carbon and energy. One problem was the slow speed: it takes the bacteria about six weeks to fully degrade a piece of PET plastic the size of a thumbnail.
However, in 2020, a UK and US team re-engineered the two enzymes into a "super-enzyme" that digests the plastic six times faster. It enables the full recycling of the bottles but scientists believe that combining the plastic-eating enzymes with existing ones that break down natural fibres could allow mixed materials to be fully recycled.
The researchers revealed an engineered version of the first enzyme in 2018, which started breaking down the plastic in a few days.
The 2018 work had determined that the structure of one enzyme, called PETase, can attack the hard, crystalline surface of plastic bottles. The researchers found, by accident, that one mutant version worked 20% faster. The scientists thought that the connection of the two enzymes might increase the speed of degradation and enable them to work more closely together.
It would be impossible for a bacterium to create the linked super-enzyme, as the molecule would be too large, so the scientists connected the two enzymes in the laboratory and saw a further tripling of the speed.
“When we linked the enzymes, rather unexpectedly, we got a dramatic increase in activity,” said Prof. John McGeehan of the University of Portsmouth, UK. “This is a trajectory towards trying to make faster enzymes that are more industrially important. But it’s also one of those stories about learning from nature and then bringing it into the lab.”
Adapted from: https://www.theguardian.com/environment/2020/sep/28/new-super-enzyme-eats-plastic-bottles-six-times-faster
1. PET may be dangerous for our body because ______________________________________.
2. In 2016, researchers in Japan ______________________________________.
3. Ideonella sakaiensis uses terephthalic acid and ethylene glycol ______________________________________.
4. Unfortunately, it takes a long time for the bacteria ______________________________________.
5. In 2018, a UK and US team ______________________________________.
6. The researchers unexpectedly discovered that ______________________________________.
7. The same team ______________________________________ two years later.
8. The linked super-enzyme could not ______________________________________ because ______________________________________.
9. According to scientists, mixed materials can also ______________________________________ by ______________________________________.
10. Prof. John McGeehan thinks that this story ______________________________________.
GLOSSARY
to break down : to destroy by accident
by accident : unexpectedly
closely : strictly
dramatic : unexpectedly big
re-engineer : to design and create again
thumbnail : the nail of the first finger on one’s hand