Dynamics and implications of biofilm formation and community succession on floating marine plastic debris

Abstract 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 little 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 (16S and 18S rRNA genes) and confocal laser scanning microscopy, we were able to profile the community and track changes in the plastisphere. 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. The successful establishment of the biofilm allowed other heterotrophic members to attach such as mixotrophic and heterotrophic dinoflagellates, zooplankton and various metazoans towards its maturation. These changes were accompanied by modifications in the both the morphology and molecular structure of the plastic surface, indicating potential degradation mediated by microbial action, making this microenvironment more habitable. This makes the plastics a hotspot of biological interactions that may 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.