Virulence-mediated colonization mechanism for TEP as a promising watershed-scale recorder and source-tracking...

Waterborne pathogens related diseases have been a global health concern. Precise source tracking of pathogens in rivers is crucial for understanding and reducing waterborne pathogens transmission risks. Current microbial source tracking techniques are still limited by identifying pathogen indicators at low concentrations, particularly in highly dynamic confluence zones of rivers where the coalescence of microbiomes exacerbates community disturbances. This study explored the potential of transparent exopolymeric particles (TEP) as effective carriers for pathogen source tracking, owing to their capacity to concentrate surrounding pathogenic bacteria as hitchhikers. The relative abundance of TEP-associated pathogenic bacteria (TAPs) was 1.61 times higher than that of overall pathogenic bacteria (OPs), which enhanced the detectability of pathogenic bacteria. Deterministic processes, particularly homogeneous selection, which accounts for 36 % of the variance, were found to govern the assembly of TAPs communities in contrast to OPs communities. In addition to nutrient and shelter functions of TEP, the selective enrichment of TAPs is mediated by virulence factors including adherence, motility, and biofilm-forming capacity, which are predominantly encoded within pathogenic bacteria. Furthermore, the relative stability of TAPs communities across watershed enabled them to record footprint of the hitchhiking pathogenic bacteria. Watershed-scale FEAST analysis confirmed superior capabilities of TAPs for source tracing than OPs, with fluctuations reduced by 0.11-32.02 %. This new MST technique based on TAPs can overcome some limitations with the traditional OPs-based methods and enables us to more precisely track pathogen sources and take evidence-based countermeasures to reduce pathogen transmission risk via rivers.