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Dynamics and implications of biofilm formation and community succession on floating marine plastic debris
Summary
An in situ 42-day exposure experiment in a tropical coastal environment tracked the stepwise colonization of polyethylene plastics by microbial communities, revealing succession from initial Gammaproteobacteria attachment through secondary colonization by cyanobacteria, diatoms, and ultimately multicellular organisms including dinoflagellates and zooplankton. The plastisphere alters both the physical structure of plastic and the dispersal of microorganisms — including potential pathogens — raising concerns about plastic debris as a vector for biological hitchhiking across ocean systems.
The formation of the plastisphere has been suggested to be a stepwise process shaped by various interactions that have implications on both the fate of the plastic and key microbial processes. However, several aspects of the colonization process by microbial communities to the recruitment of multicellular groups, and the implications of their interactions remain poorly studied. Here, through an in situ exposure experiment, polyethylene (PE) plastics were exposed in a tropical coastal environment for over 42 days. Using high throughput amplicon sequencing (16 S and 18 S rRNA genes) and confocal laser scanning microscopy, we were able to profile the community and track changes in the plastisphere. Results further showed significant changes in some abundant bacterial and eukaryotic taxa over time in plastics but not in seawater. Specifically, Gammaproteobacteria abundantly colonized the plastics from Day 1 including putative hydrocarbonoclastic bacteria. During secondary colonization, a shift in community composition was observed where photosynthetic cyanobacteria and diatoms as well as several heterotrophic Bacteroidetes increased in abundance. Our results suggest that successful establishment of the biofilm may have influence in the attachment of mixotrophic and heterotrophic members such as dinoflagellates, zooplankton, and various metazoans towards its maturation. These changes were accompanied by modifications in both the morphology and molecular structure of the plastic surface, indicating potential degradation mediated by microbial action, making this microenvironment more habitable. Biological interactions may then influence the fate of plastics such as in facilitating ingestion by larger animals, change in density properties resulting in sinking, biodeterioration leading to production of microplastics, and production of byproducts and molecules.