Microplastic-associated biofilm in an intensive mariculture pond: Temporal dynamics of microbial communities, extracellular polymeric substances and impacts on microplastics properties

Microplastics (MPs, plastic particles <5 mm) have been recognised as a novel ecological niche in the aquatic environments. Biofilm as a reservoir for opportunistic bacterial pathogens and MPs prevalence in the intensive mariculture could pose potential threats to the safety of cultured species. However, possible ecological consequences of biofilm colonising mariculture-associated MPs, such as effects on MPs fate, potential pathogens, and implications of extracellular polymeric substances (EPS) in biogeochemical cycles, are still unclear. The main objective of the present study was to investigate biota-MPs-EPS interactions in a mariculture pond. Polyethylene (PE) and polystyrene (PS), and biodegradable polylactic acid (PLA), with a mean size of ~1 mm, were exposed in situ to the pond after shrimp postlarvae were stocked. Several methods, including microscopy, spectroscopy, and high-throughput sequencing, were employed to investigate biota-MPs-EPS interactions with the shrimp growth. Genotypic data revealed distinct differences in bacterial compositions between MPs and pond water. Dissimilarities of microorganism compositions on MPs increased significantly as a function of exposure time, while microorganism abundance on MPs was co-determined by both exposure time and MPs type. Potential opportunistic pathogens, including Vibrio, Enterobacteriaceae and Tenacibaculum, were found in the mariculture-associated MPs biofilm. The attachment of predominant EPS (including proteins, polysaccharides and lipids) to MPs appeared to be reversible. Among these MPs, PE with large specific surface area exhibited higher biomass and EPS content than the other two MPs with smooth surface. Consequently, pronounced variations in physicochemical properties were observed for PE. This was the first study providing in-depth insights into the interactions of MPs-biota-EPS in the aquatic environment, which was beneficial to evaluate the seafood safety concern posed by MPs exposure to intensive mariculture. Given that the presence of pathogens on MPs surfaces and MPs covered by biofilm may raise a concern about the hazard potential of mariculture-associated MPs, efficient policies and technologies should be adopted to reduce MPs in aquaculture for facilitating sustainable and healthy development.