Microplastic biofilms as potential hotspots for plastic biodegradation and nitrogen cycling: a metagenomic perspective

Microplastics are an emerging contaminant worldwide, with the potential to impact organisms and facilitate the sorption and release of chemicals. Additionally, they create a novel habitat for microbial communities, forming biofilms known as the plastisphere. While the plastisphere has been studied in select aquatic environments, those in estuarine ecosystems merit additional attention due to their proximity to plastic debris sources. Additionally, the role plastisphere communities play in nutrient cycling has rarely been examined. This study used metagenomic analysis to investigate the taxonomic composition and functional genes of developing plastisphere communities living on petroleum-based (polyethylene and polyvinyl chloride) and biopolymer-based (polylactic acid) substrates. Isolated metagenome-assembled genomes (MAGs) showed plastisphere communities have the genes necessary to perform nitrification and denitrification and degrade petroleum and biopolymer-based plastics. The functions of these plastispheres have implications for estuarine nitrogen cycling and provide a possible explanation for the plastisphere microbes' competitiveness in biofilm environments. Overall, microplastics in the estuarine system provide a novel habitat for microbial communities and associated nitrogen cycling, facilitating the growth of microbes with plastic-degrading capabilities.