South-eastern Mediterranean plastisphere composition on five types of fossil-based plastic polymers

The south-eastern Mediterranean bacterial and fungal communities colonizing the surface of five types of fossil-based plastic polymers (LDPE, HDPE, PP, PS and PET) over a 242-day period, interrupted by a severe storm, is investigated in this work. Biofilm development was observed on all plastic surfaces. Biofilm removal by the storm was followed by recolonization and redevelopment of biofilm. Observation of the samples with scanning electron microscopy (SEM) revealed mainly dense biofilm formation, fugal hyphae, diatoms and bryozoans. Analysis of the 16s rRNa and ITS2 regions revealed that the polymer type acting as a substrate did not affect the community composition, while the biofilm phase affected only the bacterial community. Fungal species did not exhibit significant differences. Putative plastic biodegraders, as well as pathogens were detected among the colonizers. Examination of the plastic sample surfaces with Attenuated total reflection - Fourier transform infrared spectroscopy (ATR-FTIR) revealed chemical alterations for LDPE, HDPE and PP, while PS and PET remained unaffected. Polymer alterations were more pronounced during the initial colonization period. This observation coincided with the enrichment of the "Xenobiotics Biodegradation and Metabolism" pathway in the predicted metabolic profile of the bacterial communities, suggesting that the polymers were degraded by the attaching communities.