Microbial composition on microplastics mediated by stream impairment

Studies into biofilm interactions with microplastic polymers in marine environments are widespread in the literature. Increasing evidence suggests that lotic microplastics are a significant contributor and may accumulate harmful or pathogenic organisms, thereby contributing to the degradation of marine ecosystems where they meet riverine systems. Suboptimal water quality of these riverine systems may influence these biomes. This project compared the microbial diversity of biofilms that developed on microplastics to natural stone substrates in an impaired and unimpaired section of the Quinnipiac River Watershed. In this project, the influence of impairment was studied based on microbial diversity via 16S rRNA gene sequencing while monitoring total colony and fecal coliform colony counts using standard water sampling methods.

Total coliform colony counts were greater in the impaired Quinnipiac River site than in the unimpaired Honeypot Brook tributary and on the microplastic substrate than the stone substrate. Sequenced features to the class level were dominated by Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria, comprising 75% of the community biome. Simpson's Diversity indices indicated that within the two substrates, there was little variation between the communities. However, it was noted that microplastic alpha diversity trended slightly lower than the stone. Further analysis of common aquatic enteropathogens showed that the genus Citrobacter was significantly more abundant on the microplastics at both locations.

Our results indicate impaired waterbodies with a microplastic burden may retain greater fecal coliform bacterial loads than unimpaired waterbodies. Increased microplastic loads in compromised lotic systems may have an additive impact. Water quality remediation and careful monitoring are recommended to reduce this effect. Comparing this study with environmental community analysis could provide valuable insight into preferential surface attachment of bacteria onto microplastic.