A Pan-European Whole-Microbiome Study of Wastewater Influent: Prokaryotes, Protists, Fungi, and Metazoa

Microbial communities entering wastewater treatment plants (WWTPs) through untreated sewage represent an important interface between human, environmental, and treatment-associated microbiomes, yet our understanding of their biogeography remains poorly resolved, particularly for microbial eukaryotes. Using shotgun metagenomic time-series data from influent samples of seven WWTPs across a European latitudinal gradient, we analyzed the taxonomic composition and dynamics of bacteria, protists, fungi, and microscopic metazoa. Influent community composition varied with geographic location and season, with a pronounced north-south divergence driven by dominant taxa and stronger seasonal shifts observed at higher latitudes. Cross-domain associations were pervasive, suggesting that co-varying bacterial and eukaryotic components structure the incoming microbial pool. Our findings provide a pan-European baseline for whole-microbiome wastewater surveillance and highlight that influent communities differ regionally and seasonally. These patterns may be relevant for downstream treatment-stage microbiomes, but direct effects on reactor community assembly and treatment performance require targeted sampling across treatment stages.