Study of polyethylene transformation by a lignocellulolytic fungus

Plastic pollution has emerged as one of the most important environmental problems in recent decades. Managing plastic waste represents a major challenge for governments, industry and society as a whole, particularly as plastic production continues to rise in response to a growing global demand. This surge in production vastly exceeds the current technological capacity for degradation and recycling, mainly due to the high chemical stability and persistence of plastic materials.In nature, the decomposition of polymers such as lignin, cellulose and hemicellulose occurs through the action of complex microbial enzymatic systems. Inspired by these biological processes, biocatalytic depolymerization has recently emerged as a promising option for plastic degradation and recycling. In this regard, significant advances have been made in the enzymatic depolymerization of hydrolyzable plastics such as polyethylene terephthalate. However, most commercial plastics, including polyethylene, polypropylene, polystyrene, or polyvinyl chloride, are fossil-derived polymers highly recalcitrant to hydrolytic enzymes. In light of this limitation, lignocellulolytic fungi have been proposed as potential agents for transforming these materials. These fungi possess an enzymatic arsenal specialized in lignin degradation, based on oxidoreductases, which has proven effective in oxidizing highly recalcitrant compounds. Therefore, it has been hypothesized that this enzymatic system could also be active in the degradation of non-hydrolyzable plastics. To explore this hypothesis, we selected a lignocellulolytic fungal species, from a group of analyzed fungi able to grow on lignocellulose, based on its ability to induce changes in the FTIR spectra of low-density polyethylene (LDPE) when grown in the presence of this plastic. To confirm its ability to transform LDPE and identify the enzymes potentially involved in these changes, the fungus was cultivated for 60 days in the presence of this plastic under different experimental conditions, and its secretome was obtained and analyzed over time. The effects of the fungus on LDPE were evaluated using various characterization techniques. Thus, SEM revealed alterations in the plastic surface, while its oxidation was confirmed using micro-ATR/FTIR. Additionally, changes in its chemical structure and crystallinity were determined using Raman spectroscopy. The results obtained suggest that an in-depth study of the enzymatic system of this fungus could lead to the identification of promising biotechnological tools for the transformation of non-hydrolyzable plastics such as polyethylene, thereby contributing to the development of new strategies for mitigating plastic pollution.