Enviornment Prelims cum Mains

A plastic-eating enzyme can save the planet

Details :

The News:

  • Scientists have created an enzyme which can digest some of the most commonly polluting plastics, providing a potential solution to one of the world’s biggest environmental problems.

 

Background

  • In 2016, it was discovered that a bacterium had naturally evolved to eat plastic at a waste dump in Japan.
  • Researchers at University of Portsmouth and the Department of Energy’s National Renewable Energy Laboratory (NREL) in the US decoded the detailed crystal structure of the enzyme produced by the bug.
  • The structure of the enzyme looked very similar to one evolved by many bacteria to break down cutin, a natural polymer used as a protective coating by plants.
  • Researchers then tweaked the enzyme to see how it had evolved.
  • Eventually they engineered a molecule in the laboratory that is even better at breaking down the PET (polyethylene terephthalate).
  • The enzyme can also degrade polyethylene furandicarboxylate (PEF) a bio-based substitute for PET plastics that is being hailed as a replacement for glass beer bottles.
  • The researchers are now working on improving the enzyme further to allow it to be used industrially to break down plastics in a fraction of the time.
  • One possible improvement being explored is to transplant the mutant enzyme into an “extremophile bacteria” that can survive temperatures above 70C, at which point PET changes from a glassy to a viscous state, making it likely to degrade 10-100 times faster.

 

Bacteria that digests PET

  • Japanese researchers had found that a bacterial species called Ideonella sakaiensis was responsible for PET degradation.
  • The bacteria on adhering to PET surface secrete one enzyme onto the PET to generate chemical.
  • That chemical is then taken up by the cell, where another enzyme breaks it down even further, providing the bacteria with carbon and energy to grow.
  • Eventually the bacterium breaks down the entire PET chain.

What are PET plastics?

  • PET – or polyethylene terephthalate – is the most common plastic used for soft drinks bottles and polyester fibers.
  • PET plastics can persist for hundreds of years in the environment and currently pollute large areas of land and sea worldwide.
  • Properties of PET include lightweight, shatterproof, easy to mould and colour and cheap to produce.
  • The key raw material of PET is oil.

Recycling of PET

  • PET bottles that are recycled have to be cleaned, sorted by colour, then shredded and dried to produce PET flakes.
  • These can then be used to make new plastic but, due to impurities, it is not usually possible to make new, clear PET bottles.
  • Instead, recycled bottles are mostly used to make polyester fibres.
  • The recycling rates for PET bottles vary significantly around the world, from 31% in the US, to 48% in Europe, 72% in Japan and 90% in India.

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