Qian Chen,Tingting Li,Mengyao Gui,Shufeng Liu,Maosheng Zheng,Jinren Ni
Anaerobic denitrification has been proved to be negatively affected by ZnO nanomaterials (NPs), but little is known about how ZnO NPs affects aerobic denitrification. In this study, inhibition of ZnO NPs to an aerobic denitrifier, Pseudomonas stutzeri PCN-1, was firstly reported. The results showed total nitrogen removal efficiency was decreased from 100% to 1.70% with the increase of ZnO NPs from 1 to 128 mg/L. The presence of ZnO NPs caused significant inhibition of gene expressions and catalytic activities of nitrate reductase and nitrite reductase, which finally led to delayed nitrate reduction and high nitrite accumulation. Further studies revealed that the deposition of nanoparticles on the bacterial surface caused by electrostatic forces and the generation of reactive oxygen species (ROS) were responsible for the cytotoxicity of ZnO NPs, where ROS played a more important role. These results were of significance to evaluating the potential ecological toxicity and risks of nanomaterials.
The cytotoxicity of titanium dioxide nanoparticles (TiO2 NPs) to microorganisms has attracted great attention over the past few decades. As an important participator in the nitrogen cycle, aerobic denitrifiers have been proven to be negatively affected by TiO2 NPs, but the mechanism of this effect remains unclear. In this study, the bacteria-nanoparticle interaction was investigated by exposing an aerobic denitrifier, Pseudomonas stutzeri PCN-1 to different concentrations of TiO2 NPs at the dark condition, in order to investigate the cytotoxicity mechanism. The results illustrated that aerobic denitrification was inhibited at different TiO2 NPs concentrations from 1 to 128 mg/L, accompanied by the postponement of nitrate reduction and the accumulations of nitrite and nitrous oxide. But this inhibitory effect was mitigated with increasing TiO2 NPs concentrations. Further studies revealed that expressions of aerobic denitrification genes were also inhibited with the presence of TiO2 NPs, and the inhibition effect on napA and nirS genes was more significant than that on nosZ and cnorB, which might directly bring about the delayed nitrate reduction and hindered nitrite transfer. Moreover, the decreased toxicities at higher TiO2 NPs concentrations could be attributed to the formation of larger aggregates (>1000 nm), which greatly reduced the chance for direct interactions between NPs and bacterial membranes, as well as the interruption of denitrifying genes expressions. These findings were meaningful for the formation of deep insights into the mechanism of TiO2 NPs cytotoxicity as well as the development of strategies to control the negative effect of nanoparticles in the environment.Aerobic denitrification characteristics of strain PCN-1 under different carbon sources.
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.
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