Biodiversity and structure of plastisphere in lentic ecosystems

, Di Pippo Francesca, Venezia Cristina, Sighicelli Maria, Pietrelli Loris, Di Vito Stefania, Nuglio Simone, Rossetti Simona.

During transport by water flow, microplastics (MPs) can be colonised by planktonic microorganisms able to adhere to plastic surfaces with subsequent formation of biofilms. Studies investigating marine MP-associated communities reported the existence of plastic-specific microbial communities, constituting a peculiar micro-ecosystem defined ‘plastisphere'. Despite the well-documented widespread presence of MPs also in freshwater ecosystems, studies on plastisphere in these environments are still rare. This study investigated for the first time community composition and structure of microbial biofilms attached to MPs sampled from lentic ecosystems, by using 16S rRNA gene high throughput sequencing and Fluorescence In Situ Hybridization (FISH) combined with confocal laser scanning microscopy (CLSM). To address the lack of information on plastisphere microbiome composition, and to evaluate the eventual selection and recruitment of specific taxa from the planktonic community, this study analysed plastisphere and associated water communities in the main Italian lakes. Clear differences in microbial community composition among plastisphere and the corresponding planktonic populations were found. Freshwater biofilms shared a core microbiome constituted by known biofilm formers. 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. It is here suggested that MPs may select, from water column, microorganisms able to adhere to these substrata (i.e. generalist taxa as members of Sphingomonadaceae and Rhodobacteraceae families) that likely act as pioneers, thus allowing the further attachment of other microbial colonizers (i.e. members of Hyphomonadaceae, Rhizobiaceae, Rhodocyclaceae, Xanthomonadaceae and of cyanobacterial families). Interestingly, several bacterial genera previously reported to be able of degrading PE were found in plastisphere samples. This finding deserves further attention and efforts to evaluate if these micro-consortia may be good candidates for MP degradation in freshwater environments.

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