Mechanistic insights into the effects of polystyrene nanoplastics (NPs) on aerobic denitrification in Pseudomonas stutzeri PCN-1: Integrated physiological and transcriptional analysis

Polystyrene nanoplastics (NPs), ubiquitous contaminants in aquatic ecosystems, are known to impede conventional anoxic denitrification processes. However, their effects on aerobic denitrification systems remained poorly understood. This study systematically elucidates the mechanistic interactions between polystyrene NPs and aerobic denitrification performance. Results revealed polystyrene NPs caused concentration-dependent suppression of denitrification efficiency in the aerobic denitrifier Pseudomonas stutzeri PCN-1 under controlled laboratory conditions (aerobic, 30 ℃). At NPs concentrations escalating from 100 to 1000 μg L⁻¹ , nitrate removal rates decreased markedly (0.4–3.3 mg L⁻¹ h⁻¹), paralleled by progressive accumulation of nitrite (8.8–87.2 mg L⁻¹) and N₂O (31.2–58.3 mg L⁻¹). Mechanistic analyses revealed that polystyrene NPs induced biotoxic effects through two primary pathways: (1) disruption of cellular membrane integrity and (2) excessive generation of reactive oxygen species (ROS), collectively impairing bacterial viability and metabolic activity. Furthermore, critical denitrification processes were compromised, including diminished electron transport system activity, reduced catalytic activities of key denitrification enzymes, and downregulation in transcriptional expression of functional genes (e.g. napA , nirS , cnorB , and nosZ ). These multilevel inhibitions collectively contributed to the observed deterioration in nitrogen removal capacity. This investigation provides novel insights into the ecotoxicological risks posed by NPs to microbial nitrogen cycling in aquatic environments.