April 16, 2018

expert reaction to enzyme to digest plastic

Researchers publishing in PNAS have engineered an enzyme which can digest some of our most commonly polluting plastics.

Prof Adisa Azapagic FREng, Professor of Sustainable Chemical Engineering at the University of Manchester, said:

“The proposed technology could potentially be useful for plastics recycling. However, this is an early step, with significant further developments needed to demonstrate the process at a scale. A full life cycle assessment would also be needed to ensure that the technology does not solve one environmental problem (waste) at the expense of others. This includes additional greenhouse gas emissions across the reverse supply chain and related climate change impacts.”

Prof Nilay Shah, Professor of Process Systems Engineering at Imperial College London, said:

“This is a potentially very useful technology to support recovery and recycling of plastics. It should allow selective deconstruction of PET into its constituent components and therefore lead to a higher value approach to recycling such materials where mechanical recycling is not possible. In such cases, current approaches involve less sophisticated methods such as incineration.”

Prof Douglas Kell, Professor of Bioanalytical Science at the University of Manchester, said:

“Oil-derived plastics and polymers are resistant to degradation and their accumulation in the environment is an appalling problem. One of the most commonly produced plastics, e.g. as used in soft drink bottles, is polyethylene terephthalate (PET). Evolving enzymes to degrade such plastics is a high priority.

“However, natural evolution tends to produce only slow and ineffective sequences. An organism that produces an enzyme capable of degrading weakly crystalline PET, a PETase, was discovered in 2016 by a Japanese group. However, its activity on highly crystalline PET was very low. In the present work, a high-resolution structure was obtained, and it was shown that two rationally designed changes in the active site of the enzyme served to improve its properties significantly. The enzyme was also capable of degrading a novel plastic (polyethylenefuranoate, PEF) that can be produced renewably from sugars.

“This is an important advance, and further rounds of evolution, especially in regions away from the active site, should be expected to improve the enzyme yet further. All told, this advance brings the goal of sustainably recyclable polymers significantly closer.”

Prof Mark Lorch, Professor of Chemistry at the University of Hull, said:

“Bacteria and fungi co-evolved with natural materials, all the while coming up with new biochemical methods to harness the resources from dead matter. But plastics have only been in wide spread use for about 50 years. So microorganisms simply haven’t had much time to evolve the necessary biochemical tool kit to latch onto the plastic fibres, break them up into the constituent parts and then utilise the resulting chemicals as a source of energy and carbon that they need to grow. However a few years ago a group from Kyoto University isolated a new species of bacteria, from a rubbish dump, that uses PET plastics as its food source.

“This new study builds on the previous work by isolating the enzyme responsible for digesting the plastics. The team then determined the structure of the enzyme and from this worked out how the enzyme interacts with plastics molecules and then cuts them up. By inspecting this structure they concluded that there may be room for improvement, after all the bacteria had only had a few decades (at most) to evolve and so it was far from being optimal. So the team engineered the active site of the enzyme to be more efficient. The result is an enzyme that is significantly better than the naturally evolved version.

“This study represents an important step towards developing a bio-recycling method to deal with waste plastics. However, there is still some way to go. The team feel that the enzyme can be made much more efficient still, so further engineering is in order. This represents just part of the solution. The bacteria and its enzymes only deals with one class of plastic. So it maybe that a cocktail of enzymes (many of which are yet to be discovered or engineered) is required to deal with plastic waste.”

Dr Oliver Jones, Reader of analytical chemistry at RMIT University in Melbourne, said:

“I think this is very exciting work. Enzymes are non-toxic, biodegradable and can be produced in large amounts by microorganisms (bacteria and fungi). Although most people don’t know it, enzymes already help us out in many areas of everyday life such biological laundry detergents ​and in the food, leather, and textiles industries.

“This very detailed paper shows​ that there is strong potential to use enzyme technology to help with society’s growing waste problem by breaking down some of the most commonly used plastics. While there is still a way to go before you could recycle large amount of plastic with enzymes, and reducing the amount of plastic produced in the first place might​, ​perhaps​,​ be preferable, this is certainly a step in ​a positive ​direction and very exciting science ​to boot​.”

Dr Colin Miles, Head of Strategy for Industrial Biotechnology at BBSRC said:

“This is a highly novel piece of science based on a detailed molecular-level understanding of an enzyme able to depolymerise a common type of plastic, whose persistence in the environment has become a global issue. It will be interesting to see whether, based on this study, the performance of the enzyme can be improved and made suitable for industrial-scale application in the recycling and the future circular economy of plastic”.

* ‘Characterization and engineering of a plastic-degrading aromatic polyesterase’ by Harry Austin et al. published in PNAS on Monday 16 April 2018.

Declared interests

Dr Colin Miles: The study was part-funded by BBSRC.

None others received.