The word ‘plastics’ is an umbrella term used for hundreds of unique materials. Colloquially, plastics often refer to a smaller subset of high-volume and simple composition materials defined by high-volume production and simple compositions such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinylchloride (PVC), polyurethane (PUR), and polystyrene (PS) 1, 2. Despite many existing mechanical and chemical plastic recycling technologies available today, the majority of plastic is landfilled or incinerated 3, 4. The shear growth of this plastic production [5] requires both conventional and novel recycling methods to achieve international emissions and pollution goals 6, 7, 8, 9 and a circular economy. In this regard, biological plastic recycling (BPR) is an emerging technology with the potential to address the challenges and limitations of conventional recycling techniques.

BPR encompasses the use of biological catalysts (defined broadly — from proteins to consortia of cells) for the depolymerization of plastics and potential upcycling of generated monomers/oligomers (Figure 1). This broad definition indeed matches the breadth of potential applications. For example, enzymes may serve as great catalysts for industrial depolymerization, whereas organismal catalysts may be better suited for in situ bioremediation or for the consolidated upcycling of plastics (Figure 1). In this review, we intend to summarize the current prospects for BPR with a focus on the engineering and discovery of both enzymes and organisms. We will first discuss advances in the biological depolymerization and recycling of PET as it serves as the most mature example in the field and a model for other plastics. After describing the use of biocatalysts to depolymerize the other major commodity plastics, we conclude with enumerating ways in which the depolymerization products of these various plastics can be recycled or upcycled by traditional or biological means. These efforts combine to form a new type of biorefinery around plastics as a circular feedstock (Figure 1).