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June

10

2019

    SCIENCE

    Plastic — Polyethylene Terephthalate (PET)

    NEWS: Sportswear giant set to tap Indian firm’s PET project to cut virgin plastic use.
    SOURCE: The Hindu.
    WHY IN NEWS: Global sportswear giant Adidas aims at eliminating the use of virgin plastics in its products by 2024 — with a little help from a Maharashtra-based firm — the only one of its kind in the country to produce yarn out of discarded PET bottles.

    PET

    PET has been littering the environment for the last 70 years and, in 2013, 56 million tonnes of PET were produced worldwide.

    Since PET came into being only 70 years ago, a pertinent question is how this distinct bacterium evolved or naturally selected in the environment.

    Also, is not clear about the natural processes of the two unique enzymes that are capable of breaking down PET in sequential steps to evolve.

    A team of Japanese researchers has identified a bacterium species capable of breaking down plastic — polyethylene terephthalate (PET).

    The bacterium uses two enzymes in sequence to break down the highly biodegradation-resistant polymer PET – in the journal Science.

    Except for rare instances of two fungi that have been found to grow on a mineral medium of PET yarns, there are no reports any bacteria biologically degrading PET or growing on the chemically inert substance.

    250 contaminated samples from a PET bottle recycling site were collected and microorganisms that relied on PET film as a primary source of carbon for growth were looked.

    At first a distinct microbial consortium that contained a mixture of bacteria species that degraded the PET film surface at 30 degree C; 75 per cent of the PET film surface was broken down into carbon dioxide at 28 degree C were identified.

    From the microbial consortium, the researchers isolated a unique bacterium — Ideonella sakaiensis 201-F6 — that could almost completely degrade a thin film of PET in a short span of six weeks at 30 degree C.

    The bacterium degrades PET using two enzymes that act on it in sequence.

    First, the bacterium adheres to PET and produces an intermediate substance through hydrolysis.

    The second enzyme then works with water and acts on this intermediate substance to produce the two monomers — ethylene glycol and terephthalic acid — used for making PET through polymerisation.