胞外高聚物对纳米颗粒的微生物吸附吸收与毒性效应的影响及机制

Engineered nanoparticles (ENPs) have been recognized as a type of emerging contaminant with the increasing research evidences on nanotoxicity. Adsorption and internalization of ENPs by microorganisms like unicellular algae and bacteria is an important process that can regulate the nanotoxicity toward the microbes themselves and the induced eco-effect by the potential transport of the cell-accumulated ENPs within food chains. Extracellular polymeric substances (EPS) excreted by microbes can be the first fortress of the microbes to meet ENPs and are sure of playing an important role in the cell adsorption and internalization and the toxicity of the ENPs. A few studies have already indicated that EPS can influence the toxicity of some ENPs to microbes. However, the role of EPS in the cell adsorption and internalization of ENPs and the underlying mechanism of the effect of EPS on the nanotoxicity to the microbes remain to be investigated. This project is therefore mainly focused on illustrating the roles of EPS in the cell adsorption and internalization of ENPs and the toxicity of ENPs to the microbes. The green alga (Microcystis aeruginosa) and bacteria (E. coli.) will be used as the representative microbes. Multiwalled carbon nanotubes (MWCNTs), nano-Ag, nano-Fe and nano-TiO2 will be selected as the typical ENPs. Dissolved and surface-bound EPS will be isolated from the microbes. The interaction between EPS and ENPs will be investigated for the discussion of the underlying mechanisms of the roles of EPS. The adsorption and desorption of the ENPs on the EPS-coated silica surfaces will be investigated by using a quartz crystal microbalance to model the process of cell adsorption and desorption of ENPs. Batch sorption experiments will be conducted to quantitatively analyze the thermodynamic and kinetic adsorptions of the ENPs by the intact and EPS-isolated microbial cells and by the active and inactivated cells. The accumulation and distribution of ENPs on and/or in the microbial cells will be qualitatively analyzed by using some microscopy technologies. The relationship between cell adsorption and cell internalization of the ENPs will be discussed. The effect of EPS on the nanotoxicity will be addressed through investigating the dose-effect relationship between the ENPs and the intact and EPS-isolated microbes. The effect of EPS on the nanotoxicity will be further investigated through the treatment of the ENPs or the EPS-isolated microbes with the EPS previous to the nanotoxicity studies. The effects of EPS on the production of reactive oxygen species and the release of toxic metal ions of the ENPs will be examined to explain the underlying mechanism of the role of EPS on the nanotoxicity together with the effect of EPS on the cell adsorption and internalization of ENPs. The outcomes of this project will shed light on the understanding of the bioavailability and toxicity of ENPs and are expected to further the environmental risk assessment of ENPs.

越来越多的研究发现人造纳米颗粒具有生物毒性效应，其已被认为是一类新型污染物。纳米颗粒被微生物细胞表面吸附与吸收内化进入细胞是导致其毒性效应及随食物链迁移影响生态系统安全的一个重要过程。微生物分泌的胞外高聚物(EPS)是纳米颗粒接触微生物细胞的第一道屏障，必然会影响纳米颗粒的微生物吸附吸收与毒性效应。已有研究发现EPS能影响一些纳米颗粒的微生物毒性效应，但对EPS在微生物表面吸附与吸收内化纳米颗粒过程中的作用及其影响毒性效应的机制不清。本项目拟以铜绿微囊藻和大肠杆菌为测试微生物，氧化碳纳米管、纳米Fe、纳米Ag和纳米TiO2为典型纳米颗粒，在阐明EPS与纳米颗粒相互作用的基础上，重点研究EPS在微生物细胞表面吸附与吸收内化纳米颗粒过程中的作用与机制，并解析EPS对纳米颗粒微生物毒性效应的影响机制，研究结果有望加深对纳米颗粒的生物有效性和毒理机制的认识，为评估纳米颗粒的环境风险提供科学数据。

作为一类新型污染物的纳米颗粒，被微生物细胞表面吸附与吸收内化进入细胞是导致其毒性效应及随食物链迁移影响生态系统安全的一个重要过程。微生物分泌的胞外高聚物(EPS)是纳米颗粒接触微生物细胞的第一道屏障，必然会影响纳米颗粒的微生物吸附吸收与毒性效应。已有研究发现EPS 能影响一些纳米颗粒的微生物毒性效应，但对 EPS 在微生物表面吸附与吸收内化纳米颗粒过程中的作用及其影响毒性效应的机制不清。为此，本项目以蛋白核小球藻和大肠杆菌为测试微生物，提取并表征了两种微生物的EPS；通过批量吸附试验、光谱学技术等阐明了 EPS 与典型纳米颗粒相互作用机制；通过生物富集实验重点研究了EPS 在微生物细胞表面吸附与吸收内化纳米颗粒过程中的作用及机制；在此基础上，通过剂量效应实验及显微技术解析了 EPS在纳米颗粒微生物毒性效应中的作用机制。.研究发现EPS中氨基、羧基、羟基等活性官能团，能与纳米颗粒结合，改变其物化性质，从而影响纳米颗粒与微生物细胞的相互作用；纳米颗粒不仅能吸附在微生物细胞表面，也能被吸收进入微生物细胞内部。微生物细胞表面的EPS能增加藻细胞对纳米颗粒的吸附，但会阻碍纳米颗粒与细胞壁/膜的直接接触，进而抑制微生物细胞对纳米颗粒的吸收内化，降低其对微生物的氧化胁迫和毒性效应。研究结果有望加深对纳米颗粒的生物有效性和毒理机制的认识，为评估纳米颗粒的环境风险提供科学数据。在本项目支持下，共发表18篇标注论文，其中SCI论文17篇；培养了1名博士后和8名研究生。项目负责人在本项目执行期间获国家杰出青年基金资助。