The fungal plastisphere in marine and terrestrial environments: combining culture-dependent and culture-independent approaches

Plastic pollution is an environmental issue in both aquatic and terrestrial ecosystems. In 2013, the term “plastisphere” was coined by Zettler et al.1 to refer to this new human-made ecosystem where plastic debris provides a substrate that can be colonized by microorganisms through the formation of a biofilms. The study of microbial biodiversity of the plastisphere and its metabolome is therefore fundamental for the development of several biotechnological applications. Nowadays, several microorganisms are known to be promising plastic degraders, fungi included2 . This work aims to analyze the mycobiota associated with the plastisphere in both marine and terrestrial ecosystems. Marine fungi associated to different plastic polymers have been studied by means of culture dependent and independent approaches providing a wide understanding of the microbial community changes in response to anthropic pressure. Both water and sediments were considered, with sampling campaigns that involved Tyrrhenian Sea in Italy and Nordic Sea in Denmark. In the first case study, differently anthropized environments (e.g. the harbor of Livorno, a marine protected area and an intermediate point) were evaluated. When different kind of plastic polymers were used, the mycobiota did change indicating how fungal plastisphere is indeed adapted to each peculiar ecological niche. As regard terrestrial ecosystems, several fungi were isolated from a plastic-polluted landfill soil and their degradation abilities against conventional and biodegradable polymers were explored, isolating hundreds of strains. Few of them have been characterized for the capability to transform persistent (PE) and biodegradable plastics (e.g., PBS). Results showed that fungi may act against these polymers producing significant superficial modification of PE but led to an almost complete disintegration of the bioplastic. The degradation was confirmed by liquid trials where the produced transformation monomers were followed. This unexplored fungal biodiversity will be useful to face this emerging environmental problem, targeting both conventional plastics and biodegradable polymers in order to decrease the impact of plastic discharged in different ecosystems. Moreover, the enzymatic pathway involved in the degradation process would be useful to build up innovative enzymatic treatments for the waste management to allow a plastic circular economy. Finally, expanding the knowledge on plastisphere microorganisms and on their bioremediation capability would help tailoring new macromolecules accessible for microbial degradation.