Over recent decades, marine microorganisms have increasingly adapted to plastic debris, forming distinct plastic-attached microbial communities. Despite this, the colonization and succession processes on plastic surfaces in marine environments remain poorly understood. To address this knowledge gap, we conducted a microbiome succession experiment using four common plastic polymers (PE, PP, PS, and PET), as well as glass and wood, in a temperature-controlled seawater system over a 2- to 90-day period. We employed long-read 16S rRNA metabarcoding to profile the prokaryotic microbiome’s taxonomic composition at five time points throughout the experiment. By applying Weighted Gene Co-expression Network Analysis (WGCNA) to our 16S metabarcoding data, we identified unique succession signatures for 77 bacterial genera and observed polymer-specific enrichment in 39 genera. Our findings also revealed that the most significant variations in microbiome composition across surfaces occurred during the initial succession stages, with potential intra-genus relationships that are linked to surface preferences. This research advances our understanding of microbial succession dynamics on marine plastic debris and introduces a robust statistical approach for identifying succession signatures of specific bacterial taxa.

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.

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, polypropylene, polystyrene, 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.