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

The microplastic micro-interface (MPMI) in the municipal wastewater treatment system (MWTS) provides a new ecological niche for the microbiome (MGs) and potential pathogens (PPHs), facilitating both vertical and horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs) and virulence factor genes (VFGs). However, the distribution patterns and gene transfer events of PPHs, ARGs, and VFGs in MPMI remain unknown. This study examined three representative MPMIs (PET-MPMI, PE-MPMI, and PP-MPMI) colonized in the transverse gradient of MWTS using metagenomics. MGs, PPHs, ARGs, VFGs, and MGEs varied significantly across transverse gradients and horizontal interfaces. In MPMI, MGs/PPHs exhibited 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) demonstrated greater contig diversity and richness (6.44-7.36%), and adhesive VFGs provided 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, as well as the health risks of MPMI from ARG and VFG metastasis mediated by PPHs.