Microplastic-associated biofilms in a river catchment: Diversity, public health impact, and ecosystem risks

Microplastics (MPs) serve as vectors for microbial colonization and biofilm formation, posing risks to aquatic environments and public health. This study investigated the seasonal dynamics of biofilm-forming microorganisms in the Melen River catchment - a vital water source for the cosmopolitan city of İstanbul - using an environmental DNA (e-DNA) approach, which analyzes genetic material present in the environment to detect and study organisms. Polyethylene (PE) and polypropylene (PP) were the most prevalent polymers year-round, supporting the attachment of bacterial genera such as Acinetobacter, Pseudomonas, Flavobacterium, Paludibacter, and Undibacterium. A total of 70,366 and 83,327 genera were identified from water and MPs samples, respectively. The presence of pathogens such as Acinetobacter and Flavobacterium on MPs underscores significant threats to public health and aquatic food webs. Functional predictions made using PICRUSt2, a bioinformatics tool that infers metabolic pathways from 16S rRNA gene sequences, suggested that biofilm-forming bacteria on plastic surfaces may be involved in fermentation, vitamin biosynthesis, nucleoside and nucleotide degradation, and secondary metabolite degradation. These findings provide crucial insights into the ecological and health risks associated with MPs, emphasizing the role of these particles in harboring pathogens, influencing biofilm formation, and contributing to plastic degradation. This study highlights the urgent need to address MPs contamination in freshwater ecosystems to mitigate its environmental and public health risks within the framework of the 'One Health' approach.