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Reported enzymes capable of acting on polyolefin-derived plastics require a pretreatment of the plastic material 12, 14. In fact, to our knowledge, no such enzyme has been identified. The identification of enzymes from microorganisms capable of degrading untreated PE has proven a difficult task.

In the past decade, a few microorganisms have been described as capable of acting on untreated PE 17, 18, 19, 20, 21, 22, 23, although they require a significantly longer incubation time compared to experimental conditions with pre-oxidized PE. However, in most of the cases, such degradation requires an aggressive pre-treatment of PE (heating, UV light, etc.) that accelerates the incorporation of oxygen into the polymer, making the abiotic oxidation the real bottleneck of the reaction 12, 13, 14, 15, 16. Within this paradigm, several bacterial and fungal strains have been identified as capable of carrying on a certain extent of PE degradation. This is the current paradigm driving the research field in biodegradation. Once the long polymeric molecules are broken down, a process that takes years of exposure to environmental factors in the wild, bacteria or fungi intervene and continue the job 6, 9, 11, 12. The crucial first step of this chain of events, i.e., the oxidation of PE polymer, is usually carried out by abiotic factors such as light or temperature 6, 8, 10.

In the case of PE, biodegradation requires the introduction of oxygen into the polymeric chain 6, 7 this causes the formation of carbonyl groups and the subsequent scission of the long hydrocarbon chains with the production of smaller molecules, which can then be metabolized by microorganisms 8, 9. The IUPAC defines biodegradation as the “breakdown of a substance catalyzed by enzymes in vitro or in vivo” 4, later modified “to exclude abiotic enzymatic processes” 5. Biodegradation refers to environmental degradation by biological agents. In addition to mechanical and chemical recycling, biodegradation is widely considered as a promising strategy to dispose of plastic residues. Several technologies have been applied at a lab scale, although the high energetic cost might still impede the scaling up of these technological tools 3. Chemical recycling, as an alternative procedure, is preferentially aiming at plastic upcycling, e.g., decomposing polyolefin-derived plastics in order to take advantage of smaller intermediates. Several factors, such as the low number of plastic types prone to be mechanically recycled, and the low quality of the secondary products severely restrict the potential of this solution to the problem of plastic waste accumulation. To-date, only mechanical recycling is being applied at a large scale. Given the hundreds of million tons of plastic waste accumulating and the still escalating pace of plastic production, re-utilization of plastic residues is a necessary path to alleviate the gravity of the plastic pollution problem, and at the same time to render available a huge potential reservoir of carbon 2.

Together with polypropylene (PP), polystyrene (PS) and polyvinylchloride (PVC), PE is one of the most resistant polymers, with very long C–C chains organized in a crystalline, dense structure. Polyethylene (PE) accounts for 30% of synthetic plastic production, largely contributing to plastic waste pollution on the planet to-date 1.