In this study, 16S rRNA gene high throughput sequencing and Fluorescence In Situ Hybridization (FISH) combined with confocal laser scanning microscopy (CLSM) were used to assess for the first time biodiversity and structure of microplastic-associated biofilms (plastisphere) collected from Italian lentic ecosystems. The analysis revealed clear differences in microbial community composition among biofilms and corresponding planktonic populations indicating a selective adhesion on microplastics (MP). Although geographical variations in taxa composition were observed, a plastisphere core microbiome, composed by known biofilm formers found in freshwater ecosystems (e.g. Sphingorhabdus, Sphingomonas, Rhodobacter, Aquabacterium and Acidovorax genera) was found. Species composition of plastisphere did not substantially differ between the diverse polymers, while a clear link with the MP exposure time was found by Fourier Transform Infrared spectroscopy (FT-IR) and Scanning Electron Microscopy (SEM) analysis. Generalist planktonic taxa (e.g. members of the families Sphingomonadaceae and Rhodobacteraceae) were found on MPs with the lowest degradation level whereas the biodiversity increased with the increase of MP degradation. FISH-CLSM analysis confirmed the Burkolderiaceae dominance in most of the analyzed plastisphere samples and revealed a patchy microbial colonization and a complex biofilm architecture with bacterial micro-colonies and cyanobacterial aggregates occurring together with microalgae assemblages. © 2020

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