Fungi from plastics: a possible bioresources for degradation purposes

World plastic production continues to grow rapidly, from 15 million in 1964 to over 350 million today. This high production rate consequently leads to need for adequate disposal, but often it is not possible to implement a correct waste management, causing the dispersion and accumulation of plastic in both aquatic and terrestrial environments. Moreover, once released in the environment, plastic could: - undergo to physico-chemical and biological degradation processes, reducing the plastics size; - be ingested by different organisms and go up through the trophic chain; - adsorb and carry several pollutants (POPs, heavy metals, etc.) causing toxic effects on many organisms or - constitute a new ecological niche for microorganisms, pathogens included. Therefore, plastic pollution is an environmental issue and an emerging challenge to the society. In literature, several microorganisms are known to be promising plastic degraders, fungi included. Fungi are ubiquitous, playing a pivotal role in the decomposition of the organic matter, but are also known as an essential resource for the development of various biotechnological applications. Thanks to the production of extracellular and non-specific enzymes (e.g. hydrolases and oxidoreductases), several fungi can degrade very recalcitrant molecules such as lignin. This versatile enzymatic machinery allows them to attack complex and recalcitrant xenobiotics like plastics. To these days, despite the excellent results obtained on this field, the potential of these microorganisms remains largely unexplored. The study of the mycobiota associated with plastics and its metabolome is therefore of fundamental importance. These fungal bioresources could allow to expand the knowledge and development of new technologies, not only in the pharmaceutical and industrial fields, but also to a possible reduction of the environmental impact caused by the increase of plastic waste. Regarding the aquatic environment, the collaboration of different research institutes led to:the quali-quantitative evaluation of the microplastics (MPs) present both in sediments and in water column, along a transept, with different anthropic impacts, between the harbor of Livorno and a Marine Protected Area and the study of the marine microbiota associated with the MPs, combining a metagenomic and culturomic approach. More in details, this work is aimed to analyze the mycobiota associated with the MPs and in the sediments in the three sites cited above. In order to maximize the fungal biodiversity, the isolation phase was carried out by using different solid medium (MEA, SNA and CMA) with the addition of sea salt and using two different incubation temperature (15-25°C). A polyphasic approach has been used for the specific identification, which involves the combination of molecular analysis with specific markers and the morpho-physiological characteristics assessment. Preliminary results show that the mycobiota is dominated by Ascomycota Phylum: the most abundant genera are Penicillium and Cladosporium followed by the Basidiomycota yeast Sporobolomyces. The sediments showed a greater specific richness than MPs. For instance, Zygomycetes and some genera (e.g. Rizhopus, Trichoderma, Aspergillus) were exclusively associated to MPs. As regards the terrestrial environment, a plastic-polluted landfill soil was studied. After a long enrichment phase, a rich fungal biodiversity was brought to light: 95 strains belonging to 14 genera and 27 species were isolated. Most of fungi belonged to Ascomycota phylum, whereas only 2% of fungi were Mucoromycota. The fungal community was dominated by Fusarium, Purpureocillium and Aspergillus, that alone covered almost 70% of isolated fungi. The actual role of these strains in the plastic-associated community was investigated. Fungi were preliminary screened for their capability to grow in the presence of polyethylene (PE) powder as sole C source. The solid screening showed that most of fungi (97%) indeed were capable of developing in this condition. Many strains, mostly belonging to Fusarium and Aspergillus genera, did tolerate high concentration of PE. Only few strains confirmed this degradation skills on a less accessible and available matrix as a thick PE film. Since the microbial attack usually begins with a colonization and adhesion on the surface, FT-IR and SEM were a useful tool to observe the effects of the fungal treatment. F. oxysporum, F. falciforme and P. lilacinum gave the most promising results. They could actively transform PE and caused the strongest oxidation phenomena, as assessed by FT-IR results. Moreover, they also affected the PE film morphology, which was then plenty of cavities, grooves and a flaking structure appeared on the surface of the film.