Biodegradation

Who doesn’t use plastics? Be it packaging, electronic equipment, household equipment, safety equipment, and even vehicles, plastics are part of our life. Plastic is very much omnipresent in every aspect of our daily lives. 7 commonly produced types of plastic (that you also might heard of) are: PET (or PETE or Polyester) (polyethylene terephthalate), PVC (polyvinyl chloride), PP (polypropylene), PS (polystyrene), HDPE (high-density polyethylene), LDPE (low-density polyethylene), and miscellaneous plastics (i.e. polycarbonate, polylactide, acrylic, acrylonitrile butadiene, styrene, fiberglass and nylon). PET, a petroleum based substance, is a nonbiodegradable substance. Despite that, it is the most commonly used one, say like plastic bottles and food packaging. In consequence, our Earth is dying of it.

We can find plastic garbage in big cities and even in the most remote areas because of their extensive applications. Around the world, nearly a million plastic beverage bottles are sold every minute, while 5 trillion plastic bags are used every year. However, most of these plastics are used just once, then tossed, which causes many environmental problems. As an example, more than 5 trillion pieces of plastic are already floating in our oceans. By 2050, scientists predict every seabird species on the planet will be eating plastic. It may not be our waste - but it is our one and only planet! There was no light for these environmental problems because of the huge numbers of plastic waste, however, it all changed in 2016 thanks to the discovery of plastic-eating bacteria.

Source: Yoshida et al., 2016

In 2016, a group of scientists from Kyoto Institute of Technology and Keio University comprises Shosuke Yoshida, Kenji Miyamoto, Emeritus Kohei Oda, and Emeritus Yoshiharu Kimura held a cooperative research project with Teijin Limited and ADEKA Corporation. A bacterium (later named Ideonella sakaiensis), isolated from a cluster of microorganisms in the sediment sample from a Japanese bottle recycling factory waste dump, was found to be able to use PET as their food. An enzyme called PETase was discovered to be responsible for this bacteria’s plastic-eating ability. This discovery means that scientists could also ‘transplant’ the plastic-eating ability to other desired bacteria, making a bigger possibility to design a bio-recycling outline for synthetic polymers by using microbes.

Source: Yoshida et al., 2016

However, there are also some limitations of using microbes to degrade plastic waste that have to be coped with, for example, the dependency on PET substrate existence or the supplement of expensive carbon sources into the culture for growing. Furthermore, Ideonella sakaiensis and other microorganisms used so far to degrade PET cannot adapt well in the marine habitats where lots of plastic waste compiles. Therefore, the organisms are not suitable for bioremediation of PET polluted saltwater, and the usage of microbes to degrade plastic waste in the ocean is still out of reach.

Despite plentiful problems left to be solved, lots of further applications using PETase are possible. Further studies and experiments of the molecular system of PETase will give an appropriate direction for the forthcoming recognition of relative enzymes. Some studies have shown that we can increase the activity of PETase by lowering PET crystallinity, but we also need to find out a way to make the enzyme perform well at a bigger temperature where the degree of PET crystallinity is smaller.

That being said, PETase from Ideonella sakaiensis could be a feasible solution to reduce plastic waste in our environment. Let’s cheer the scientists as they are trying to break the impossible! - and while we’re trying to keep the waste minimum too!