The plastic in question is called polyethylene terephthalate – or more simply, PET. First patented in 1941, PET has a variety of applications, but one of the most common is its use in plastic bottles.
I’m sure we’ve all seen pictures like the one at the top of this article. And maybe you’ve heard about the growing plastic islands in the world too? Even though PET is one of the most recyclable plastics, with recycled uses in polyester fibres, carpet fibres & non-food containers, only 31.2% of PET was recycled in the US in 2013. Their European counterparts at least managed to recycle a rather better figure of 56%. Sadly though, the rest of it ends up in landfills and in the oceans, being neither pretty nor useful, and often harming animals and the environment.
But what’s the solution? A couple of weeks ago, a paper was published in Science describing a new species of bacteria, called Ideonella sakaiensis, which is able to use PET as food. Although the process is slow – taking up to 6 weeks to degrade a small piece of plastic film – this represents a potential game changer in the world of plastic recycling.
So how does it work? In the 60 – 70 years since PET was patented and introduced, I. sakaiensis has evolved 2 enzymes – PETase & MHETase – to digest PET. First PETase breaks down PET into MHET (that stands for Mono(2-hydroxyethyl) terephthalic acid if you’re curious). Then the MHETase enzyme breaks down MHET into 2 simpler products, ethylene glycol and terephthalic acid. Finally these 2 products are used by the bacteria as its sole carbon source. Yum, plastic!
The idea is to one day use these bacteria, and more specifically the enzymes they produce, as a form of environmental remediation to deal with the other 69% (thank you America) of PET that is not recycled, as well as using them for biological recycling of PET waste products. But that doesn’t mean that you can just chuck your plastic bottles out!
Holder, M., Europeans recycle 65 billion PET bottles in 2013 – letsrecycle.com. Available at: http://www.letsrecycle.com/news/latest-news/europeans-recycle-65-billion-pet-bottles-2013/ [Accessed April 3, 2016].
PET recycling rate posts slight increase in 2013 – RT – Recycling Today. Available at: http://www.recyclingtoday.com/article/pet-recycling-rate-napcor-apr/ [Accessed April 3, 2016].
Yoshida, S. et al., 2016. A bacterium that degrades and assimilates poly(ethylene terephthalate). Science, 351(6278), pp.1196–1199.