Department of Environmental Science and Engineering, School of Energy and Environment, Wuxi Engineering Research Center of Taihu Lake Water Environment, Southeast University, Nanjing, Jiangsu, 210096, China; Key Laboratory of Environmental Medicine Engineering, Ministry of Education, Southeast University, Nanjing, Jiangsu, 210009, China.
Key Laboratory of Environmental Medicine Engineering, Ministry of Education, Southeast University, Nanjing, Jiangsu, 210009, China.
Chemosphere. 2018 Mar;195:693-701. doi: 10.1016/j.chemosphere.2017.12.078. Epub 2017 Dec 13.
Although the antibacterial performances of emerging nanoparticles (NPs) have been extensively explored in the nitrifying systems, the impacts of dissolved oxygen (DO) levels on their bio-toxicities to the nitrifiers and the impaired cells' recovery potentials have seldom been addressed yet. In this study, the physiological and transcriptional responses of the typical ammonia oxidizers - Nitrosomonas europaea in a chemostat to the chronic ZnO NP exposure under different DO conditions were investigated. The results indicated that the cells in steady-growth state in the chemostat were more persevering than batch cultured ones to resist ZnO NP stress despite the dose-dependent NP inhibitory effects were observed. In addition, the occurred striking over-expressions of amoA and hao genes at the initial NP exposure stage suggested the cells' self-regulation potentials at the transcriptional level. The low DO (0.5 mg/L) cultured cells displayed higher sensitivity to NP stress than the high DO (2.0 mg/L) cultured ones, probably owning to the inefficient oxygen-dependent electron transfer from ammonia oxidation for energy conversion/production. The following 12-h NP-free batch recovery assays revealed that both high and low DO cultured cells possessed the physiological and metabolic activity recovery potentials, which were in negative correlation with the NP exposure time. The duration of NP stress and the resulting NP dissolution were critical for the cells' damage levels and their performance recoverability. The membrane preservation processes and the associated metabolism regulations were expected to actively participate in the cells' self-adaption to NP stress and thus be responsible for their metabolic activities recovery.
尽管新兴纳米颗粒 (NPs) 的抗菌性能在硝化系统中得到了广泛的研究，但溶解氧 (DO) 水平对其生物毒性对硝化菌的影响以及受损细胞的恢复潜力却很少被提及。在这项研究中，考察了在不同 DO 条件下，典型氨氧化菌——欧洲亚硝化单胞菌在恒化器中对慢性 ZnO NPs 暴露的生理和转录响应。结果表明，尽管观察到剂量依赖性的 NP 抑制作用，但在恒化器中处于稳定生长状态的细胞比批培养细胞更能抵抗 ZnO NP 应激。此外，在 NP 暴露初期，amoA 和 hao 基因的显著过表达表明细胞在转录水平上具有自我调节潜力。低 DO（0.5mg/L）培养的细胞对 NP 应激的敏感性高于高 DO（2.0mg/L）培养的细胞，这可能是由于氨氧化的氧依赖性电子转移效率较低，无法为能量转换/产生提供足够的能量。随后进行的 12 小时无 NP 批处理恢复实验表明，高 DO 和低 DO 培养的细胞均具有生理和代谢活性恢复的潜力，这与 NP 暴露时间呈负相关。NP 应激的持续时间和 NP 的溶解程度是细胞损伤水平及其可恢复性的关键。膜保护过程和相关的代谢调节可能积极参与细胞对 NP 应激的自适应过程，从而对其代谢活性的恢复负责。
