Dr Elizabeth Bell, who led the experimental work at the MIB, says of the platform; "The accumulation of plastic in the environment is a major global challenge. For this reason, we were keen to use our enzyme evolution capabilities to enhance the properties of plastic degrading enzymes to help alleviate some of these problems. We are hopeful that in the future our scalable platform will allow us to quickly develop new and specific enzymes are suitable for use in large-scale plastic recycling processes."
To test their platform, they went on to develop a new enzyme, HotPETase, through the directed evolution of IsPETase. IsPETase is a recently discovered enzyme produced by the bacterium Ideonella sakaiensis, which can use PET as a carbon and energy source. While IsPETase has the natural ability to degrade some semi-crystalline forms of PET, the enzyme is unstable at temperatures above 40°C, far below desirable process conditions. This low stability means that reactions must be run at temperatures below the glass transition temperature of PET (~65°C), which leads to low depolymerisation rates. To address this limitation, the team developed a thermostable enzyme, HotPETase, which is active at 70°C, which is above the glass transition temperature of PET.
This enzyme can depolymerise semi-crystalline PET more rapidly than previously reported enzymes and can selectively deconstruct the PET component of a laminated packaging material, highlighting the selectivity that can be achieved by enzymatic recycling. Professor Anthony Green, Lecturer in Organic Chemistry, said: "The development of HotPETase nicely illustrates the capabilities of our enzyme engineering platform. We are now excited to work with process engineers and polymer scientists to test our enzyme in real world applications. Moving forward, we are hopeful that our platform will prove useful for developing more efficient, stable, and selective enzymes for recycling a wide range of plastic materials."
The development of robust plastic degrading enzymes such as HotPETase, along with the availability of a versatile enzyme engineering platform, make important contributions towards the development of a biotechnological solution to the plastic waste challenge. To move this promising technology forward will now require a collaborative and multidisciplinary effort involving biotechnologists, process engineers and polymer scientists from across the academic and industrial communities. With the world facing an ever-mounting waste problem, biotechnology could provide an environmentally sustainable solution.