Monthly Popular Science Magazine

A Plastic Eating Enzyme: Hope For Recycling
And Fighting Pollution

Researchers have identified and engineered an enzyme which can digest and consume some of our most commonly polluting plastics providing a hope for recycling and fighting pollution


 

 

Polluting plastics is the biggest environmental challenge worldwide in the form of plastic pollution and the best solution to this problem still remains elusive. Most plastics are made from petroleum or natural gas which are non-renewable resources that are extracted and processed using energy-intensive techniques. Thus, their manufacturing and production itself is very destructive for fragile ecosystems. Also, the destruction of plastic (mostly by incineration) causes air, water and land pollution. About 79 per cent of the plastic produced over the last 70 years has been thrown away, either into landfill sites or into the general environment while only about nine per cent is recycled with the rest incinerated.This process of incineration exposes vulnerable workers to toxic chemicals which include cancer-causing substances. The oceans are said to contain some 51 trillion microplastic particles and are slowly depleting the marine life. Some of the plastic microparticles get blown away in air leading to pollution and it’s a real possibility that we might be inhaling them. No one could have predicted in the 1960s that the advent and popularity of plastics would one day become a burden with huge plastic waste found floating in our beautiful oceans and air and dumped on our precious lands.

The plastic packaging is the biggest threat and most corrupt use of plastics. But the problem is that the plastic bag is everywhere, used for every little purpose and there is no control over its usage. This kind of synthetic plastic does not biodegrade, instead just sits and accumulates in landfills and contributes to environmental pollution. There have been initiatives for “complete plastic ban”, especially polystyrene which is used in packaging. However, this is not leading to desired results as plastic is still ubiquitous in land, air and water and is ever growing. Safe to say that plastic may not even be visible to the naked eye all the time but it’s everywhere! Its sad that scientists who discovered the “extraordinary” plastic material are unable to tackle the material’s recycling and dispose problem.

In a breakthrough study published in Proceedings of the National Academy of Sciences USA, researchers have discovered a known natural enzyme which feeds on plastic. This was a chance discovery while they were examining the structure of an enzyme which was generally found in waste which is ready to go for recycling at a centre in Japan. It was discovered that this enzyme, called IdeonellaSakaiensis 201-F6, is able to “eat” or “feed off” the patented plastic PET or polyethylene terephthalatewhich is most commonly used in millions of tons of plastic bottles. The enzyme basically allowed the bacterium to degrade the plastic as their food source. No recycling solutions currently exists for PET and these plastic bottles persist for more than hundreds of years in the environment. So, this study led by teams at the University of Portsmouth and the United States Department of Energy's National Renewable Energy Laboratory (NREL) has generated immense hope.

The original goal of the authors was to determine the three-dimensional crystal structure of this natural enzyme (called PETase) and use this information to understand how exactly this enzyme works. They used an intense beam of X-rays - which are 10 billion times brighter than sun - to elucidate the structure by seeing individual atoms. Such powerful beams enabled to understand the inner working of the enzyme and provided the correct blueprints to be able to engineer faster and more efficient enzymes. It was discovered that PETase looks very similar to another enzyme called cutinase except that PETase has a special feature and a more “open” active site, which is thought to accommodate human-made polymers (instead of the natural ones). These differences immediately indicated that PETasemay be more evolved specially in a PET-containing environment and thus could degrade PET. To test what they were thinking researchers mutated thePETase active site to make it look more like cutinase. What followed was a totally unexpected outcome, the PETase mutant was able to degrade PET even better than the natural PETase. Thus, to their luck, in the process of understanding and trying to improve the natural enzyme’s capability, they ended up accidently engineering a new enzyme which was even better than the natural enzyme in breaking down PET plastics. This enzyme could also degrade polyethylene furandicarboxylate, or PEF, a bio-based substitute for PET plastics.This generated hope to tackle other substrates like PEF (Polyethylene Furanoate) or even PBS (Polybutylene succinate). The tools for enzyme engineering and evolution can be continually applied for further improvement. Researchers are looking at a way for improving the enzyme so that its function could be incorporated in a powerful large-scale industrial set up. The authors state that the engineering process is very much similar to enzymes which are currently being used in bio-washing detergents or in manufacture of biofuels. Simply put, the technology exists and thus industrial viability should be achievable in the coming years.

However, this discovery is also laden with some apprehensions which will take time to be resolved after further work has been carried out.  Firstly, the enzyme breaks down larger pieces of plastics into smaller pieces, therefore it does support recycling of plastic bottles but all this plastic needs to be first recovered. This “smaller” plastic when recovered could be used to turn them back to plastic bottles. The enzyme cannot really “go and find plastic on its own” in the environment. One proposed option could be to plant this enzyme into some bacteria which can start breaking down plastic at a higher rate while withstanding high temperatures. Also, long term impact of this enzyme still needs to be comprehended.

It is absolutely no doubt that the impact of such an innovative solution to tackle plastic waste would be very high on a global scale. The world has been trying to tackle the plastic problem ever since the advent of plastic itself. There have been laws banning single-plastic use and also recycled plastic is now favoured everywhere. Even small steps like banning plastic carry bags in supermarkets has been all the over the media. The point is, we really need to act fast if we would like to preserve our planet from plastic pollution. Though we must carry adopting recycling in our everyday life while encouraging our children to do so as well. We still need a good long-term solution which can go hand on hand with our own individual efforts. This research is preliminary and it only marks a beginning but it is definitely aiming at tackling one of the biggest problems which mankindor our planet is facing.

Source:

Harry P et al. 2018, ‘Characterization and engineering of a plastic-degrading aromatic polyesterase’, Proceedings of the National Academy of Sciences, DOI: https://doi.org/10.1073/pnas.1718804115

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Vol.1 Issue 5 May 2018

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