The plastisphere has been widely studied in the oceans; however, there is little information on how living organisms interact with the plastisphere in freshwater ecosystems, and particularly on how this interaction changes over time. We have characterized, over one year, the evolution of the eukaryotic and bacterial communities colonizing four everyday plastic items deployed in two sites of the same river with different anthropogenic impact. α-diversity analyses showed that site had a significant role in bacterial and eukaryotic diversity, with the most impacted site having higher values of the Shannon diversity index. β-diversity analyses showed that site explained most of the sample variation followed by substrate type (i.e., plastic item) and time since first colonization. In this regard, core microbiomes/biomes in each plastic at 1, 3, 6 and 12 months could be identified at genus level, giving a global overview of the evolution of the plastisphere over time. The measured concentration of antibiotics in the river water positively correlated with the abundance of antibiotic resistance genes (ARGs) on the plastics. These results provide relevant information on the temporal dynamics of the plastisphere in freshwater ecosystems and emphasize the potential contribution of plastic items to the global spread of antibiotic resistance The authors acknowledge the financial support provided by the Spanish Government (Ministerio de Ciencia e Innovacion, ´ MICIN): PID2020–113769RB-C21/22, PLEC2021–007693 (Funded by MCIN/ AEI/10.13039/501100011033 and by the European Union “NextGenerationEU”/PRTR”), the IMPASSE project (PCIN-2017–06) belonging to the EU JPI-Water initiative, and the Thematic Network of Micro- and Nanoplastics in the Environment (RED2018–102345-T, EnviroPlaNet Network). SMC thanks the Universidad de Alcala ´ for the award of an FPI contract. A. Rico thanks the Talented Researcher Support Programme - Plan GenT (CIDEGENT/2020/043) of the Generalitat Valenciana. The authors gratefully acknowledge the Genomics Unit of the “Parque Científico de Madrid” for qPCR experiments and Illumina sequencing
