The　accumulation　of　micro/nanoplastics　in　wastewater　significantly　hinders　denitrification　in　biological　wastewater　treatment　systems,　yet　the　intrinsic　mechanisms　are　not　fully　understood.　Herein,　we　combined　signal　molecule　monitoring,　electrochemical　characterization　and　multi-omics　analysis　to　investigate　how　quorum　sensing　(QS)-mediated　microbial　interactions　influence　denitrification　in　aerobic　granular　sludge　systems.　Results　showed　that　after　90-day　exposure　to　micro/nanoplastics,　cross-talk　between　multiple　signal　molecules　significantly　declined,　thereby　disrupting　the　QS　system　to　opportunely　sense　changes　in　the　external　environment.　As　a　consequence　of　impaired　QS,　only　5　species　exhibited　up-regulation　of　the　genes　encoding　amino　acids　and　cofactors　to　sustain　cross-feeding,　while　others,　acting　as　＇cheaters＇,　relied　on　metabolites　offered　by　cross-feeding　but　without　reciprocating.　This　imbalance　resulted　in　insufficient　availability　of　metabolites,　including　redox-active　metabolites　such　as　riboflavin,　and　subsequently　deteriorated　the　denitrification　electron　transfer　process.　Compared　to　the　control　group,　the　extracellular　electron　transfer　capacity　and　denitrification　electron　transfer　chain　activity　decreased　to,　respectively,　88.08　%　and　63.33　%　(microplastics-exposure)　and　79.64　%　and　63.75　%　(nanoplastics-exposure),　which　directly　contributed　to　the　decline　in　nitrogen　removal.　Overall,　this　study　provided　deeper　insights　into　the　denitrification　in　complex　microbial　communities　under　the　stress　of　micro/nanoplastics　from　the　perspective　of　QS-mediated　microbial　social　behavior.　©　2025　Elsevier　Ltd