| With the rapid development of nanotechnology, nanoparticles (NPs) are widely applied in many industrial and living products, which mean that an increasing number of nanoparticles will be released to sewage treatment systems through production, transportation, application, disposal processes or pollution accidents. The potential influence of NPs on sewage treatment systems has thus got more and more widely attention and needs to be explored. The aim of this study was to investigate the short-term (6h) effects of single NPs (n-TiO2, n-CeO2 or n-ZnO) and coexisting NPs on indicative nitrite bacteria(Nitrosomonas europaea) in biological nitrogen removal system. Compare the differences between them and summarize the rule of effect, then provide necessary theoretical support for the further study of NPs on sewage treatment system and mechanism research.The study of single toxicity found that with 6h incubation, three kinds of NPs all showed obvious biological stress effect on N.europeae. Meanwhile, there was a positive correlation between the biological stress and the additive concentration of NPs. When under the same concentration, n-ZnO had the largest toxic effect, in turn were n-CeO2 and n-TiO2. Toxicity of n-ZnO is due to the size effect of itself, because that the experimental group of 50mg/L n-ZnO on the cell membrane damage and ammonia oxidation inhibition was significantly higher than that of its corresponding solubility Zn2+. In addition, the toxicity of Zn2+ on N.europeae was higher than n-ZnO with the same molar concentration.The study of coexistence toxicity found that when n-TiO2 mixed with n-ZnO or n-CeO2, n-TiO2 would lower the toxicities of n-ZnO or n-CeO2 on N.europeae. At the same time, the degree of toxicity reduction has a positive correlation with the added n-TiO2 concentration. On the other hand, n-CeO2 mixed with n-ZnO would increase the toxicity of n-ZnO on N.europeae. The examined parameters had different sensitivity to NPs stress and the cell membrane was most sensitive for NPs, which indicated the cell membrane damage as an important NPs toxicity exertion pathway.By using reverse transcription real-time quantitative polymerase chain reaction PCR technology (RT-qPCR) and genome-wide expression level spectrum detection technology (microarray gene chip technology) to analyze the whole genome expression of N.europeae after their exposure to NPs. n-TiO2 mixed with n-ZnO or n-CeO2 would increase the expression of amoA gene. Meanwhile, the expression of amoA has a positive correlation with the n-TiO2 concentration. In constract, n-CeO2 would decrease the expression of amoA when it mixed with n-ZnO. In addition, the amoA gene expression profile was different from of the AMO enzyme activity, which suggested that NPs AMO enzyme activity inhibition might through mRNA translation impairment, NPs combining with the enzyme active site or destroying the cell membrane structure. n-ZnO showed the strongest stress among the three NPs on the hao gene expression, while n-TiO2 showed the least. The biological stress of NPs would stimulate the expression of some stress response genes such as reaction regulatory genes and chemotaxis genes and down-regulated the expression of some gene related to translations such as tRNA pseudouridine synthase and adenosine transferase. Microarray gene chip technology also further confirmed that n-TiO2 would lower the toxicities of n-ZnO or n-CeO2 on N.europeae and n-CeO2 mixed with n-ZnO would increase the toxicity of n-ZnO. The biological toxicity effect of NPs to N.europeae has a close relationship with its additive concentration, solubility, and charge in water, and at the same time affect cell morphology and physiological function and the function of micro molecular gene expression and activity of key enzyme. |
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