Time-driven plastisphere: Temporal dynamics shape the marine microplastic microbiome under natural field conditions.

Microplastics (MPs) are well-recognized as vectors for microbial colonization, forming complex biofilms known as the plastisphere. In this study, we investigated the colonization of four common plastic polymers, namely Linear Low Density Polyethylene (LLDPE), Polyethylene Terephthalate (PET), Polystyrene (PS), and Polyvinyl Chloride (PVC) with an average size range of 3.2-4.1 mm by marine microorganisms under natural shallow coastal water column conditions (∼2 m depth) near the fishing port of Gabès, in southeastern Tunisia (Gulf of Gabès, southern Mediterranean Sea). Biofilms were monitored over 7, 30, and 90 days using 16S rRNA gene amplicon sequencing to assess the simultaneous effect of exposure time and polymer type. Temporal succession emerged as the dominant driver of plastisphere composition, with PERMANOVA revealing that exposure time explained 58% of the total community variance (p = 0.001), while polymer type accounted for 15% (p = 0.001). Distance-based redundancy analysis (db-RDA) further demonstrated that this successional trajectory was closely associated with seasonal environmental shifts. Proteobacteria, Campylobacterota, Bacteroidota, and Actinobacteriota dominated the plastisphere, with Rhodobacteraceae, Saprospiraceae, and Flavobacteriaceae consistently established throughout. Putative hydrocarbonoclastic and plastic-associated taxa were detected at different stages of biofilm development, alongside organisms promoting biofilm cohesion. PET supported the most diverse biofilm, harboring approximately 2400 ASVs, including nearly 900 unique ASVs, after three months of exposure, whereas PVC hosted the most distinct microbial communities.