纳米氧化铈作用下活性污泥胞外聚合物及溶解性微生物产物特性

Characterization of extracellular polymeric substance and soluble microbial products under impact of Ce O2 nanoparticles

【目的】纳米氧化铈作为一种应用普遍的人工纳米材料,其生物毒性和环境效应得到了越来越多的重视。尝试从微生物代谢产物的角度,解读纳米氧化铈对活性污泥微生物的影响规律和过程。【方法】在实验室活性污泥系统中投加不同质量浓度纳米氧化铈,研究纳米氧化铈短期作用下微生物胞外聚合物(EPS)和溶解性微生物产物(SMP)这两类主要的微生物代谢产物含量和组分的变化规律。【结果】短期作用下,EPS和SMP的总量都随着纳米氧化铈浓度的增加而增加。低浓度纳米CeO_2不会导致活性污泥中松散型胞外聚合物(LB-EPS)、紧密型胞外聚合物(TB-EPS)含量和组分的显著改变。高浓度纳米CeO_2(25 mg/L以上)作用下TB-EPS含量和组分不受影响,而LB-EPS中多糖和蛋白质为抵抗纳米CeO_2毒性而增多。EPS分层组分含量显著提高,且LB-EPS的增幅显著高于TB-EPS增幅。当纳米氧化铈浓度为50 mg/L时,相较于空白对照组,蛋白质和多糖增幅分别达到35.18%和46.57%。当纳米氧化铈超过25 mg/L以上时,SMP不仅出现蛋白质,多糖和腐殖酸的含量也明显增加。【结论】SMP中蛋白质的产生,可能会与纳米材料相结合,以减小纳米材料的毒性。当纳米氧化铈浓度较低时,EPS的吸附作用会抵制其进入细胞内,当纳米氧化铈浓度较高时,刺激细胞产生更多EPS吸附纳米CeO_2,形成更厚的外部屏障层保护细胞。EPS和SMP的共同作用,构成了微生物细胞对纳米CeO_2的毒性抵抗机制。

[Objective] With the universal application of CeO_2 nanoparticles（CeO_2 NPs）, its biological toxicity and environmental effect have been paid more and more attention. The purpose of this study was to acquire the process and influence of CeO_2 NPs on activated sludge from activated microorganisms metabolites. [Methods] EPS and SMP are the two main types of microbial metabolites, the content and composition of which were both examined after dosing different concentrations of CeO_2 NPs in laboratory-scale activated sludge. [Results] The content of EPS and SMP increased with the increasing dosage of CeO_2 NPs during a short period. The content of TB-EPS and LB-EPS didn＇t have changed observably at low concentration of CeO_2 NPs. The content of TB-EPS and its compositions were not significantly affected, while the polysaccharide and protein of LB-EPS increased for resistant to the toxicity of CeO_2 NPs（more than 25 mg/L）. Compared to the control upon exposure to CeO_2 NPs（50 mg/L）, the protein and polysaccharide increased 35.18% and 46.57% respectively. The content of two types of EPS increased in the presence of CeO_2 NPs, and LB-EPS increased significantly higher than the LB-EPS growth. When the concentration of CeO_2 NPs was more than 25 mg/L, the content of protein of SMP appeared, polysaccharide and humic also increased significantly as well. [Conclusion] The protein generated from SMP might be combined with nanometer materials to reduce the toxicity of nanomaterials. At the low concentration of CeO_2 NPs, the adsorption effect of EPS would prevent CeO_2 NPs from passing into the cell. However, when the concentration was higher, CeO_2 NPs would stimulate the microorganisms to produce more EPS which could form a thicker outer barrier layer to protect cells better. EPS and SMP worked together to resist the toxicity of CeO_2 on microbial cell.