Microplastics (MPs) serve as carriers for microbial community colonization, forming unique ecosystems known as plastispheres in urban aquatic ecosystems. However, interactions among microbes, extracellular polymeric substances (EPS), and MPs remain poorly understood. This study investigates microbial consortia and their EPS secretion behaviors across various plastispheres at two representative coastal urban water sites. Permutational multivariate analysis of variance revealed that MP type significantly influenced microbial community structures in reservoir environments (R² = 0.60, p < 0.001), highlighting the pronounced impact of MP types in high-quality urban waters. Specific microbial phyla and genera were identified as key contributors to EPS compositional variations across different plastispheres. Hierarchical partitioning results identified Acidobacteria, Nitrospirae, and Planctomycetes as influential phyla positively affecting EPS composition. Spearman correlation analysis pinpointed Robiginitialea (positive correlation) and Fimbriiglobus (negative correlation) as critical genera influencing EPS dynamics. Moreover, EPS-related gene abundance corresponded closely with observed EPS compositional differences. Dominant genes associated with protein biosynthesis included xapD in reservoirs and glnA in bays, while glmS and eno were predominant for polysaccharide biosynthesis in bays. This research advances our understanding of microbial-EPS-MP interactions in urban water systems, offering critical insights into ecological remediation and risk assessment of MP pollution.

The scarcity of electron acceptors in municipal wastewater hampers nitrogen removal in anaerobic ammonium oxidation (anammox) systems, limiting their wider adoption. Electrochemically-assisted anammox (E-AMX) addresses this by using electrodes as alternative electron acceptors to nitrite (NO₂⁻), thereby enhancing electron transfer and reducing NO₂⁻ dependency. However, the underlying nitrogen metabolism and extracellular electron transfer (EET) mechanisms in E-AMX require further exploration. Here, we employed metagenomic sequencing to elucidate nitrogen-metabolic pathways and EET mechanisms in an E-AMX system, focusing on key functional genes and extracellular polymeric substances (EPS) synthesis genes. The genetic potential for pili synthesis in Candidatus (Ca.) Brocadia was, for the first time, revealed through binning analysis. Under a 0 V (vs. Ag/AgCl) electric field, E-AMX achieved stable and efficient operation on day 27 with near 100% ammonia and NO₂⁻ removal. The abundance of Ca. Brocadia increased to 13.9% (1.9× that of the control), accompanied by more abundant core anammox genes (hzs and hdh). These results allow the prediction of the nitrogen-metabolism pathway in E-AMX. Functional gene profiling indicated that direct EET relied chiefly on heme, the Mtr pathway, flagella and pili. Additionally, the electric field increased copies of EPS-associated amino acid metabolism genes (e.g., cysK, thrC), which likely facilitated protein-mediated indirect EET. Binning analysis further revealed selective enrichment of Ca. Brocadia sinica, indicating species-level niche differentiation under the electric field. This study proposes potential mechanisms by which an applied micro-electric-field enhances anammox activity and EET, offering theoretical clues for future optimization of electric-field-driven nitrogen removal processes.