Plastic substrates shape prokaryotic community structure and resistance gene assemblages in tropical coastal waters

Aquaculture environments in tropical coastal regions are increasingly exposed to plastic debris, creating novel microbial habitats with the potential to disseminate antibiotic resistance genes (ARGs). We deployed plastic substrates in situ for 21 days at a coastal aquaculture site in Singapore, profiling substrate-attached prokaryotic communities using long-read environmental DNA sequencing. Polypropylene (PE) and polyethylene (PP) plastics supported distinct microbial assemblages that diverged over time and differed by polymer type, while seawater hosted greater overall species richness. Despite comparable alpha diversity, PE and PP biofilms demonstrated diverse taxonomic and functional gene profiles, with substrate-driven enrichment of metabolic pathways. Fifteen classes of ARGs were detected, with increased diversity and abundance on plastics, and ARG patterns were correlated with salinity, turbidity, and chlorophyll. This study provides the first long-read characterization of plastisphere biofilms and their associated ARGs in tropical aquaculture systems in Southeast Asia. These findings position aquaculture plastics as reservoirs for diverse prokaryotes and resistance genes, highlighting their ecological and food safety implications in tropical coastal systems.