Structural alteration of low density polyethylene by ligninolytic fungi

Plastics are essential in the global economy due to their durability and versatility in a wide range of applications. Global plastic production exceeded 413 million tons in 2023 (Plastics Europe, 2024). As a result, plastic wastes have become ubiquitous and have accumulated in the environment impacting ecosystems and wildlife. There is therefore an urgent need to explore alternative approaches to effectively reduce plastic waste without affecting negatively the environment. Since 2016, significant progress has been made in the biodegradation of polyesters such as PET from plastic bottles, through bacteria that produce esterase-type enzymes (Yoshida et al., 2016). However, other olefin-type plastic polymers are non-hydrolysable or have not yet been shown to undergo microbial degradation. Several studies suggest the potential of saprotrophic fungi for degradation of synthetic polymers due to their prominent role in the decomposition of organic matter in soil and their metabolic versatility (Zeghal et al., 2021). The LIG2PLAST project focuses on studying the degradative potential of wood-decaying basidiomycete fungi and other lignocellulose-degrading species to address this challenge. This study leverages knowledge generated by our research group on lignocellulose biodegradation to assess the potential of these fungi (and their enzymes) to transform non-hydrolysable plastics. We selected a fungal species showing robust colonization on low-density polyethylene (LDPE) films in Petri-dish cultures. It was subsequently grown in liquid culture under induction conditions, and LDPE films were added to analyze the secreted enzymes and their effects on the plastic. Through direct visualization and scanning electron microscopy (SEM), fungal colonization and alterations in the surface of the film were observed. Additionally, FTIR-ATR analysis and Raman spectroscopy revealed significant changes in the chemical structure of the plastic. Finally, we analysed the exoproteome of the fungal liquid culture, and identified an enhancement of CAZymes, which might be responsible for the modifications observed in the treated plastic.