Polyethylene (PE) is the most abundantly produced plastic in the world, accounting for 30-40% of all synthetic polymers, with an annual global production of nearly 100 million tonnes in 2018. It is found in an extensive array of commonly used items, such as grocery bags, milk cartons and sponges. Due to its low economic cost, it is frequently adopted for single use functions, resulting in large quantities of PE waste. PE is durable, which is appealing for commercial purposes, but creates a major environmental problem as it can indefinitely persist in landfills after being discarded, with only around 10% of the total PE mass produced being recycled. PE degradation (both abiotic and biotic) occurs at a rate that cannot keep pace with current production, inevitably resulting in a build-up of plastic in the environment with detrimental consequences.
The biodegradability of PE could be increased by enhancing natural biological processes through directed protein evolution. It has been known for nearly 50 years that degradation of PE is affected by microbes. Many studies have identified organisms capable of facilitating the degradation of PE, and in some cases the proteins responsible. However, these strains and enzymes are typically poorly characterized or inefficient. Directed protein can be used to improve the efficiency of enzymes, sometimes resulting in increases of reaction rates by many orders of magnitude. However, this impactful technology has yet to be applied to the challenge of polymer biodegradation. We have isolated bacterial strains capable of growth on Polyethylene as a sole carbon source, and have identified a protein element involved. This protein element can now be subjected to protein evolution campaigns to improve its activity.
