Characterization of Microplastic-Associated Biofilm Development along a Freshwater-Estuarine Gradient

Microplastic contamination is an increasing concern worldwide. Biofilms rapidly develop on surfaces in aquatic habitats, but the processes of biofilm formation and variation in bacterial community succession on different microplastics introduced into freshwater and estuarine environments are not well understood. In this study, the biofilm bacterial communities that developed on three different types of microplastics that are prevalent in the environment, high-density polyethylene (HDPE), polyethylene terephthalate (PET), and polystyrene (PS), was investigated. Virgin microplastics were incubated in microcosms over a period of 31 days with water collected along a freshwater-estuarine gradient of the Raritan River in New Jersey. Through long-read MinION sequencing of bacterial ribosomal operons, we were able to examine biofilm bacterial communities at a species- and strain-level resolution. Results indicated that both salinity level and microplastic type impacted biofilm formation and promoted colonization by distinct microbial communities. Limnobacter thiooxidans was found to be one of the most abundant microplastics colonizing-bacteria, and it is hypothesized that different types of microplastics could select for different strains. Our findings indicate that multiple groups of highly similar L. thiooxidans rRNA operons could be discerned within the community profiles. Phylogenetic reconstruction further established that various Linmobacter species uniquely colonized the different microplastics from the different sampling sites. Our findings indicate that microplastics support abundant and diverse bacterial communities and that the various types of microplastics can influence how different bacterial biofilms develop, which may have ecological impacts on aquatic ecosystems.