Science News

Potential of the Plastic-Degrading Enzyme, Discovered by Accident

2018 is the year of plastic-consuming consciousness, and who can blame us? Plastics can take up to 1,000 years to decompose; an especially-worrying prospect considering only 14% of plastic bottles are recycled and that many plastics remain non-recyclable. When our waste has filled the land, plastics can then are disposed into the oceans. These inevitably end up on our beaches (the best-case scenario; the worst being the carcass of an animal washed ashore, killed by simply mistaking a foreign plastic object as a food source). For those who don’t feel as passionately about reducing plastic waste, it is worth finding out about how our plastic consumption is affecting the planet, and perhaps then you may think a little differently…

A lot of measures have been implemented recently to reduce plastic consumption; hooray! But what about all the existing plastic that has not yet degraded? And although we can reduce our usage, we aren’t cutting it out completely, so what can we do about that?

In a new breakthrough, microbiology may have the answer. Scientists have discovered an enzyme (a protein used in reactions) that can degrade commonly-used plastics. By accident.

This all began in 2016, when scientists found a bacterium on a Japanese landfill with some special properties. Bacteria has a very short generation time. We may have had children by the age of 30, but bacteria could have gone through nine generations in just three hours. As there are more generations within a shorter time, this also means that bacterium can evolve much more quickly to their environments than we ever could. These bacterium, which could only survive off the landfill, consequently evolved the ability to degrade plastic so that it could be used as a food source to survive. Amazing!

The species, Ideonella sakaiensis, was able to break down Polyethylene Terephthalate (PET), which is a plastic used extensively in products such as bottles, containers and packaging. Two enzymes hydrolyse (chemical breakdown using water in the reaction) the plastic into monomers (building blocks for growth, such as amino acids, glucose and nucleotides) that can then be used by the bacterium.

Inspired by this breakthrough, scientists investigated the structure of the enzymes involved in degrading the plastic to create a mutant enzyme by making tweaks to see how it evolved. As a result, they made the enzyme BETTER at its job. They beat the bacteria to it!

The research, published in the Proceedings of the National Academy of Sciences journal, looked at the structure of the enzyme by using the Diamond Light Source (Oxford, UK),  an intense beam of X-rays that can reveal individual atoms. The structure was revealed to be very similar to that of a commonly-found enzyme in bacteria that breaks down cutin, another polymer found on the protective layer of plants.

Professor John McGeehan, who led the research at the University of Portsmouth, said; “What we are hoping to do is use this enzyme to turn this plastic back into its original components, so we can literally recycle it back to plastic”. He added that “it means we won’t need to dig up any more oil and, fundamentally, it should reduce the amount of plastic in the environment”.

The enzyme takes a couple of days to start breaking down the plastic, but this is nothing compared the hundreds of years it naturally takes. Scientists are also optimistic that they can further improve the enzyme so that the plastic can be broken down even more quickly.

Although recycling plastic should always be encouraged, most of the products can only be turned into opaque fibres for clothing or carpets. This new enzyme may also offer the opportunity to not only degrade clear plastic bottles, but also allow them to be turned back into new plastic bottles, hence reducing the requirement to produce new plastic. There is an attraction to continue to produce more PET products as they require oil for its production, which is cheap, but now there is now pressure to reduce production and increase recycling. The new enzyme may be the solution to this.

What are the next steps? One possible improvement is to transplant the mutant enzyme into bacteria that can withstand extreme heat, and then expose the bacteria to plastic that is being melted in the hope that the plastic will be degraded more quickly. Although it has been shown that some fungi have the same properties, bacteria are much easier to use in industry. Whilst enzymes can be produced in large amounts by bacteria, there is still a long way to go before there would be enough to substantially reduce plastic waste.

For now, don’t just rely on the scientists to reduce plastic waste; try to have that drink without a plastic straw!

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