PETase – a theoretical solution, or a viable one?

Lots of plastic bottles placed upright - symbolic of plastic pollution

Earlier this year, the news broke that scientists had discovered a bacteria that ate plastic. Scientists in Japan analysed microbes living in sludge samples near a Japanese PET bottle recycling site. After five years and 250 samples, the bacterium Ideonella sakaiensis was found. This bacterium can digest plastic.

The discovery wasn’t made a minute too soon, because the plastic pollution problem has gained massive proportions. Every year, over 300 million tonnes of plastic is created, roughly half of which is discarded after single use. That’s over 400 million kgs every day. Of the 8.3 billion tonnes of plastic created till date, 79% is lying in dumpsters (or in the sea) today. Plastic is wonderful, but single-use plastic is not.

An island of plastic twice the size of Texas is floating around in the Pacific Ocean. In 2016, 480 billion disposable plastic bottles were sold globally. That equates to roughly a million bottles a minute. Of these, around a quarter are manufactured by Coca-Cola alone. Less than 25% of plastic bottles are recycled in the United States.

Now, about the miracle plastic-eater.

The bacterium I. sakaiensis uses an enzyme called PETase to break down and digest plastic. PET plastic is digested and converted to terephthalic acid and ethylene glycol, which are the raw materials used to create plastic. Neither of them is harmful to the environment, and they can be further broken down into carbon dioxide and water.

(Note here that the bacterium itself isn’t called PETase – the enzyme it uses to digest the plastic is. Since most articles name PETase rather than I. sakaiensis in titles, that’s a misconception many people seem to have. Not that I blame the writers – repeatedly mentioning I. sakaiensis does take away from the readability a fair bit.)

Scientists believe that the bacterium evolved to eat PET plastic, since it was in an area with copious amounts of it. Plastic was invented a mere 70 years ago, and for a life form to have evolved to subsist entirely off it so quickly is rather impressive.

Now, there have been numerous reports of bacteria (and other creatures) that eat plastic, in the past. Worms, fungi, and heaven knows what else. What makes this any different? Is it a viable solution to the plastic pollution problem? We’ll discuss that in this article.

Let’s start by discussing why the bacterium is better than past discoveries of plastic-consuming creatures.

Well, for starters, it’s real.

Secondly, Ideonella sakaiensis is easy to cultivate. In most cases in the past, like with the pestalotiopsis microspora fungus, they could only be cultivated in tricky conditions. This bacterium isn’t as choosy. All it needs is the right temperature, some good old PET plastic, and time.

Thirdly, the bacterium really chows through plastic – meaning it eats quickly. Not as fast as we’d like, but much faster than natural forces otherwise did. In nature, plastic takes hundreds of years to biodegrade. A plastic bottle, for instance, can take anywhere between 100-600 years to break down.

The bacterium cuts this down to a matter of weeks – or months, at most. Researchers found that a thumbnail sized piece of PET plastic needed 6 weeks at 30 degrees Celsius to fully break down. From 600 years down to 6 weeks. That’s slow by industrial standards, but…

There’s another reason yet. The enzyme that I. sakaiensis uses to digest plastic can be – and has been – engineered to make it better. Scientists accidentally created a mutant enzyme that’s 20% more efficient than naturally-occurring PETase. NREL structural biologist Bryon Donohue said, in an interview, “After just 96 hours you can see clearly via electron microscopy that the PETase is degrading PET.”

This means that the enzyme can be further optimized, so future versions could be much better at eating plastic – and therefore of use for industrial purposes.

This is great news, because it means that it’ll be possible to fully recycle plastic for the first time. At present, plastic isn’t truly recycled. What’s done in recycling centres is, the waste plastic is melted and made into different products. So there’s no opportunity to decontaminate the plastic, or to turn it into raw material and start afresh.

That poses a problem, because a lot of companies prefer ‘virgin’ plastic – i.e., plastic made freshly, out of raw materials. In other words, a majority of companies don’t use recycled plastic in packaging.

With the help of PETase, recycled plastic will actually be ‘virgin’ plastic, so it’ll all really be reusable! The enzyme could be added to vats of waste plastic, and the resultant raw materials could then be used to make fresh plastics.

Another great thing about PETase is that it digests PET or PETE – one of the most widely-used plastics in the world. PET is used commonly in disposable bottles, bags, containers, and ropes. There are many other types of plastic, a few of which aren’t in wide use today. An enzyme that digested those wouldn’t make as much of a difference.

So, the answer to the question is – Ideonella sakaiensis is a potentially viable solution. Meaning, it’s not viable at present, but there’s reason to believe that it will be in the not-too-distant future. It’s a glimmer – or shall I say a big, blinding flashlight beam – of hope.

 

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