Decoding the microplastic Micro-interface: a complex Web of gene transfer and pathogenic threats in wastewater

• MP micro-interfaces show enhanced microbial stability and durability. • Pathogens encoding multidrug resistance genes dominate MP interfaces. • Pathogens significantly drive ARG and VFG enrichment on MP interfaces. • MGE-mediated ARG transfer occurs preferentially via pathogens on MPs. • Microbiome, pathogens, MGEs, VFGs directly affect ARGs on MP interfaces. The microplastic micro-interface (MPMI) in the municipal wastewater treatment system (MWTS) provides a new ecological niche for the microbiome (MGs) and potential pathogenic (PPHs), facilitating both vertical and horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs) and virulence factor genes (VFGs). In the transverse gradient and horizontal interface of the MPMI in MWTS, gene transfer chain events and the distribution patterns of PPHs, ARGs, and VFGs remain unknown. This study examined three representative MPMIs (PET-MPMI, PE-MPMI, and PP-MPMI) colonized in the transverse gradient of MWTS using metagenomics. MPMI MGs, PPHs, ARGs, VFGs, and MGEs varied significantly across transverse gradients and horizontal interfaces. In MPMI, MGs/PPHs had better connectivity and robustness (closeness centrality 19.51/21.45 and betweenness centricity 19.66/14.07), ARG hosts (mostly Escherichia coli and Salmonella enterica ) showed greater contig diversity and richness (6.44–7.36%), and adhesive VFGs had superior competitive advantages. Additionally, MPMI shows a more complex and persistent coexistence pattern of MGs, ARGs, and VFGs (54.30–57.25%), increasing pathogenicity risk. MPMI accelerates the HGT of ARGs mediated by MGEs at the horizontal interface and transverse gradients through PPHs, with MGs, PPHs, MGEs, and VFGs directly influencing the alterations in ARGs within MPMI. This study developed a conceptual framework to understand MPMI gene co-occurrence and transfer across transverse gradients and interfaces and the health risks of MPMI from ARG and VFG metastasis mediated by PPHs.