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Re-engineering bacteria to eat plastic

Plastic pollution accounts for around 14 million tonnes of plastic ending up in the earth’s oceans every year. From entangling them, to suffocating, them to ending up in the bodies of sea creatures, plastic pollution is having a massive impact on ocean ecosystems which in turn has the potential to affect human health.

Microplastics that may have been contaminated can leak toxins into the creatures that ingest them, with concomitant consequences for their predators and also the human food chain. According to reports, only around 15% of all plastic produced is recycled into new plastic and most of it is either incinerated or stays in landfill, both of which potentially result in the release of toxic fumes.

However, according to the journal Science, scientists found that a species of bacteria was eating its way through some plastic bottles which had been left outside a recycling facility. The bacteria – Ideonella sakaiensis – was absorbing the plastic polyethylene terephthalate (PET).

Analysis showed that Ideonella sakaiensis produced two digestive enzymes. PETase or hydrolysing PET break down the long molecular chains of the plastic into monomers (shorter trains) of terephthalic acid and ethylene glycol, which in turn break down themselves releasing energy for the bacteria to grow.

Having established that Ideonella sakaiensis bacteria in effect, eats the plastic, genetic scientists have tried to develop methods to improve the efficiency with which it does it. One research focus has been to genetically engineer bacteria that are more efficient at enzyme production and turn them into PETase generators.

In another research initiative, researchers at Portsmouth University have combined PETase with an enzyme called MHETase by attaching their DNA together to create an enzyme which increases its plastic digestion capability by a factor of 6 and can also break down the sugar-based bioplastic Polyethylene furanoate (PEF).

In addition, researchers at Edinburgh University used E.Coli and converted plastic into vanillin, the primary constituent of vanilla bean extract. In effect, PET plastic was reduced to its basic monomers, one of which – terephthalic acid – was converted to vanillin after a series of further chemical reactions.

If, after further research, this vanillin is deemed suitable for human consumption, then in a huge global market for vanilla, 85% of which is made from chemicals taken from fossil fuels, using plastic could be an extremely ecologically sound substitute.

However, PETase only breaks down PET plastic and there are 6 other types of plastic that as yet cannot be broken down using enzymes. Whilst the potential for use of plastic-eating bacteria is great, more research will be needed for the process to become widespread commercially.

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