Triggering and identifying the polyurethane and polyethylene-degrading machinery of filamentous fungi secretomes

The uncontrollable disposal of plastic waste has raised the concern of the multidisciplinary community, which tries to face this environmental burden by discovering and applying new techniques. Regarding the biotechnology field, several important microorganisms possessing the necessary enzymatic arsenal to utilize recalcitrant synthetic polymers as an energy source have been discovered. In the present study, we screened various fungi for their ability to degrade intact polymers, such as ether-based polyurethane (PU) and low-density polyethylene (LDPE). For this Impranil and a mixture of long-chain alkanes was used, not only as sole carbon sources but also as enzyme indicators and inducers for polymer degradation. An agar plate screening revealed three fungal strains belonging to Fusarium and Aspergillus genera, whose secretome was further studied for its ability to degrade the respective polymers. Specifically for ether-based PU, the secretome of a Fusarium species reduced the sample mass and the average molecular weight of the polymer by 24.5 and 20.4 %, respectively, while the secretome of an Aspergillus species caused changes in the molecular structure of LDPE, as evidenced by FTIR. At the same time, the proteomic analysis revealed that the enzymatic activities induced in presence of Impranil can be associated with urethane bond cleavage, a fact which was also supported by ether-based PU degradation. Meanwhile, the mechanism of LDPE degradation was not completely elucidated, although the presence of oxidative enzymes could be the main factor contributing to polymer modification.