The invisible threats of sunscreen as a plastic co-pollutant: Impact of a common organic UV filter on biofilm formation and metabolic function in the nascent marine plastisphere.

Plastic debris in marine environments serves as a substrate for microbial colonisation, forming biofilms known as 'plastispheres'. Also accumulated on plastic debris are co-pollutants including UV-protective organic UV-filters from sunscreens, which likely interact with this niche through their lipophilicity. Despite their widespread use and environmental accumulation, the influence of UV-filters on plastisphere composition and function has never been investigated. This study therefore investigates, for the first time, how co-pollution - specifically by an organic UV-filter - impacts the composition and function of marine plastisphere communities. To achieve this, low-density polyethylene (LDPE) was incubated with marine microbial communities for six days to cultivate a nascent plastisphere, which was then exposed to 5 mg/L of EthylHexyl MethoxyCinnamate (EHMC); the most used organic UV-filter in sunscreens, and a prevalent marine pollutant. Metagenomic analyses revealed that EHMC favoured the growth of bacterial generalists Pseudomonas and Psychromonas while reducing pollutant-degrading genera like Marinomonas. Analysis of 3070 proteins revealed a consistent upregulation of proteins used for biofilm maintenance by Pseudomonas with EHMC exposure, including the considerable upregulation of outer membrane porin F (OprF) which regulates exopolymeric substance (EPS) production. Additionally, proteins thought to indicate a shift from aerobic to anaerobic respiration were frequently expressed after exposure to EHMC. This may have selected against the obligate aerobes Marinomonas and Pseudoalteromonas, contributing to the observed shift in community composition. These findings underscore the importance of considering chemical co-pollutants in plastisphere research as we now begin to discover how ecologically significant, and potentially harmful microbial genera are affected by this interaction.