Plastics play an indispensable role in our daily lives due to their high resistance to chemicals and corrosion, their robustness and lightness. However, their durability, the ever-increasing consumption of plastics and the limitations of conventional waste management methods, generate enormous quantities of plastic waste that accumulate in the natural environment and cause a serious global pollution problem.

The search for innovative solutions for plastic treatment and recycling has brought to light the potential of biocatalytic depolymerisation as a promising option, which aims to reduce adverse environmental effects and recover valuable components from plastic waste to manufacture new plastic products or synthesise other value-added chemicals in a circular way. In the last decade, significant progress has been made in this field with the discovery and engineering of microbial enzymes capable of hydrolysing polyesters such as polyethylene terephthalate. However, most commercial plastics are polymers derived from fossil hydrocarbons that are recalcitrant to the action of hydrolases. Although biotransformation of non-hydrolysable synthetic polymers has only been outlined in a few studies, the potential of wood-degrading fungi for this purpose has been demonstrated.

Wood-decay fungi secrete a powerful oxidative enzymatic machinery composed of an array of oxidoreductases to degrade the recalcitrant aromatic polymer of lignin (inert to the action of hydrolases). These enzymes are also efficient detoxifying a range of organic pollutants. In LIG2PLAST we will take advantage of the know-how generated by our research group on lignin degradation during over 25 years of research to evaluate the potential capabilities of these ligninolytic fungi and their enzymes to transform non-hydrolysable plastics. Cultivation of fungi in the presence of synthetic polymers and subsequent physicochemical characterization of the degradation products will provide the first evidences of the ability of these organisms to transform plastics. Secretomic analyses will be carried out to identify the potential enzymes (and auxiliary proteins) involved in this degradation process. The analysis will be extended with the in silico screening of fungal genomes for new enzymes, and the evaluation of the recombinant oxidoreductases currently available in our group, as well as ancestral ligninolytic enzymes that will be resurrected in the project. Heterologous expression and characterisation of the most promising enzymes (and auxiliary proteins) in polymer transformation (alone or in enzymatic cocktails, directly or through the action of redox mediators) will be followed by the improvement of their properties. Directed evolution and rational design assisted by computational simulations of extant and resurrected enzymes will be used to design efficient biocatalysts for the deconstruction of non-polyester plastics.

All this will help to achieve the main objective of LIG2PLAST, which is to increase knowledge about microorganism and enzymes capable of transforming non-hydrolysable plastic polymers, with the ultimate aim of developing new biotechnological tools for plastic degradation and recycling, thus contributing to reduce the environmental impact of plastic waste.