Plastic-Colonizing Fungi in the Eastern Mediterranean Sea: Community Structure and Physiological and Transcriptional Responses of Aspergillus to Pristine and Weathered PET

Marine plastic debris provides persistent artificial substrates for microbial colonization, yet the fungal component of the plastisphere remains poorly characterized. Using ITS metabarcoding and culture-based isolation approaches, we characterized the early mycobiome associated with polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) plastic pellets deployed in an Eastern Mediterranean Sea (EMS) marina. The sequence-based communities were taxonomically heterogeneous, with only a limited effect of polymer type. Ascomycota, Zoopagomycota, and Basidiomycota were the dominant phyla identified by the ITS sequence analysis, while Linderina and Starmerella were the dominant genera. In contrast, the cultured isolates belonged exclusively to the phyla Ascomycota and Mucoromycota, with the Aspergillus genus accounting for 52.3% of the isolates. We further recorded physiological responses of 11 Aspergillus isolates to pristine and UV-weathered PET, including attachment, pigmentation, and plastic gravimetric weight loss. A. niger OC26 also exhibited strong peroxidase activity, together with a broad transcriptional response to PET exposure, including 216 upregulated genes and significant enrichment of peroxidase- and membrane-associated functions. UV weathering induced a limited but distinct additional transcriptional shift. Together, these findings indicate that early plastic-associated fungal communities in the EMS are taxonomically diverse and include metabolically versatile Aspergillus strains that mount distinct physiological and transcriptional responses to PET exposure.