Fungi and plastisphere: can this biodiversity hide biotechnological powerful biocatalysts?

Despite the current efforts to limit the impact of plastic on the environment, we cannot oversee the actual risk the entire ecosystem is exposed to. The mycobiota associated to the plastisphere is poorly-studied, with very few information available about its degrading skills. Our research purpose is to investigate extreme polluted environments, including plasticpolluted landfill soil and organic waste treatment plants, as well as marine water and sediments. The microbial community was studied through culturomic and metagenomic approaches, focusing the attention of both traditional polymers and bioplastic. The isolated fungal community differed a lot, with a strong role of the site, the plastic material and environmental parameters as the salinity. Hundred strains were isolated, mostly associated with the Ascomycota phylum. Despite the filamentous fungi were very abundant, yeasts were not neglectable (approx. 10%). Studies confirmed that environmental parameters differently affect the microbial community. Populating the plastisphere cannot be considered as an axiom of being capable of transforming plastic. Studies were focused on the evaluation of this phenomenon: growth screenings were followed by liquid culture to quantitatively measure the polymer transformation yields. Many fungal strains (i.e. Alternaria, Aspergillus, Cladosporium, Fusarium, Penicillium, Purpureocillium) showed the capability to degrade plastic polymers with the consequent production of monomers. Fungi were also tested against different polymers and in peculiar environments, including sea water, agricultural soils and organic treatment plants. In a model marine environment, selected fungi did transform bioplastics, even though halving the yields obtained in fresh water. Moreover, when used as pre-treatment of plastic for further anaerobic digestion, they helped to strengthen and fasten bioplastics degradation. Fungal biodiversity has indeed proven to be involved in the transformation of plastic materials, resisting the harsh working conditions, but the involved metabolic pathways has still to be discovered.