Plastic eating microbes to the rescue: evolution may be finding a solution to the problem of plastic waste

plastic waste
CC BY 2.0 Sustainable Initiatives Fund Trust (Sift)

Last week Sami covered news that microplastics are found in 93% of bottled water and the highest microplastic contamination levels ever were found in an English river.

The preferred solution to pollution requires acting at the source to prevent the contaminants from entering the environment in the first place. But as it is clear there is already a big mess to clean up, and as we probably won't stop using plastics today, it seems worth looking at progress in managing the problem. So we circled back around on Ideonella sakaiensis 201-F6 (i. sakaiensis for short), a microbe that Japanese scientists found merrily munching away on polyethylene terephthalate (PET).

It has long been known that if you give a population of microbes a reduced level of food source and a lot of contaminants that they could chew on if they get hungry enough, evolution will do the rest. As soon as one or two mutations favors digesting the new (contaminant) food source, those microbes will thrive - they now have unlimited food, compared to their friends trying to survive on traditional sources of energy.

It therefore makes perfect sense that the Japanese scientists found that evolution has achieved the same miracle in the environment of a waste plastic storage facility, where abundant PET exists for the dining pleasure of any microbe that could bust the enzyme barrier and learn how to eat the stuff.

Of course, the next step is to figure out if such natural talents can be used to serve humanity. The i. sakaiensis has proven to be more efficient than a fungus that was described earlier as contributing to the natural biodegradation of PET -- which takes centuries without the help of this newly evolved microbe.

Scientists of the Korea Advanced Institute of Science and Technology (KAIST) have reported the most recent advances in study of i. sakaiensis. They have succeeded to describe the 3-D structure of the enzymes used by i. sakaiensis, which can help in understanding how the enzyme approaches "docking" to the large PET molecules in a manner that allows them to break down the material which is usually so persistent because natural organisms have not found a way to attack. This is a bit like being at the point where the medieval castle can no longer serve as a key defense, since mechanisms to overcome the previously impenetrable fortresses were discovered.

The KAIST team also used protein engineering techniques to make a similar enzyme that is even more effective at degrading PET. This sort of enzyme could be very interesting for a circular economy, in that the best recycling will come from breaking post-use materials back down to their molecular constituents, which can them be reacted to new materials of the same quality as materials made from the fossil fuels or recovered carbon from which the initial product was generated. Thus 'recycled' and 'virgin' materials would be of equal quality.

Distinguished Professor Sang Yup Lee of the Department of Chemical and Biomolecular Engineering of KAIST said,

"Environmental pollution from plastics remains one of the greatest challenges worldwide with the increasing consumption of plastics. We successfully constructed a new superior PET-degrading variant with the determination of a crystal structure of PETase and its degrading molecular mechanism. This novel technology will help further studies to engineer more superior enzymes with high efficiency in degrading. This will be the subject of our team's ongoing research projects to address the global environmental pollution problem for next generation."

We bet his team won't be the only ones, and will watch eagerly as the science of i. sakaiensis evolves.

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