Exploiting the fungal community against plastic polymers

When proper plastic disposal does not happen, both intentionally or unintentionally, natural ecosystems are the main recipients. Conventional plastic is persistent due to the high stability to chemical and physical stressors. In 2018, European plastics production reached 61.8 million tons, while only 29.1 million tons were collected. It has been estimated that worldwide, 2 billion people have no access to adequate waste collection system. When plastic reaches aquatic and terrestrial ecosystems, the effects can be seen along the entire trophic chain, also due to fragmentation in microfragments. On the other hand, bioplastics are considered a safe alternative, even though they cannot be underestimated. When not properly disposed, their degradation may be slow and partial, jeopardizing the ultimate sustainability of the process. Likely, nature responds to bioplastic presence by evolving and adapting an active microbiota. The study of the plastisphere and its metabolome is therefore fundamental for the development of several biotechnological applications. This work aims to analyze the mycobiota associated with plastics in a terrestrial environment and investigate their degrading skills against plastic polymers. Extreme polluted environments were studied, including plastic-polluted landfill soil and compost plants, with different anthropic impacts. A rich fungal biodiversity was isolated and identified. Fungi have been studied to evaluate their capability to mediate an active transformation of plastic polymers. Many strains confirmed this assumption. The actual capability of some fungi to degrade plastic was followed by means of growth studies and integrated analytical methods, as ATR-FTIR analyses and SEM investigation. As expected, at first, polymer biodegradation started as a superficial erosion process: the microorganisms colonize the surface and adhere, with the production of extracellular enzymes and other secretions to form a biofilm. Many fungi have been found capable to actively transform not only conventional plastic but also bioplastic, posing the basis for the development of bio-integrated technologies to strengthen their degradation leaving a harmless environment. Trials were performed both in solid and liquid conditions, investigating few factors that may affect the process, as the temperature or the presence of other accessible C source to activate the primary metabolism. During the degradation in liquid media, HPLC-RI analyses highlighted the presence of several degradation metabolites, confirming then the depolymerization ability. The degradation products completely matched the monomer components of the tested polyesters, no unknown peaks were detected. However, their transformation rate was not always comparable, indicating that fungi may have a peculiar affinity towards few compounds. To investigate this aspect, the selected fungi was used to treat monomers at different concentrations, highlighting concentration effect and different assimilation rate. Additional efforts are now aimed to better characterize the mycobiota of plastisphere, identify the best fungal degraders and the enzymes involved, and to enlarge the studied plastic polymers.