两种粒径纳米银对Nitrosomonas europaea的毒性效应

为明晰不同粒径纳米银（AgNPs）对欧洲亚硝化毛杆菌（Nitrosomonas europaea）的毒性效应，采用室内培养方式，探究10nm和50nm的AgNPs对N.europaea生长、氮转化能力、细胞结构、活性氧生成和功能基因表达的影响.结果表明，AgNPs暴露抑制N.europaea生长，随着暴露时间的延长，细菌生长抑制率增加，在4h达到最大值；培养基中NH₄⁺向NO₂^-转化速率减缓，N.europaea的铵态氮转化能力降低；扫描电镜（SEM）图像显示AgNPs造成部分细菌表面塌陷且有孔洞，细胞膜受损严重；透射电镜（TEM）图像显示AgNPs造成细菌内部核物质消融，细胞质膜界限模糊；流式细胞仪（FCM）检测发现AgNPs增加细胞内活性氧的生成；qRT-PCR技术对AgNPs暴露后N.europaea功能基因amoA、hao、merA表达进行测定，发现AgNPs抑制N.europaea功能基因的转录表达.综上所述，AgNPs通过与细胞膜相互作用和产生氧化应激损伤N.europaea，抑制amoA和merA的表达，进而影响铵态氮转化过程，且小粒径AgNPs的毒性强于大粒径.

Toxicity of two sizes of silver nanoparticles to Nitrosomonas europaea

The laboratory incubation experiments were conducted to study the toxicity of silver nanoparticles with different particle sizes on Nitrosomonas europaea, and the effects of two sizes of nanosilver (10nm and 50nm) on the bacterial growth, nitrogen transformation, cellular structure, reactive oxygen generation and gene expression were investigated. The results showed that nanosilver inhibited the growth of N. europaea. With the extension of exposure time, the inhibition rate of bacterial growth activity increased and reached to maximum at 4h. In the medium, the transformation rate of NH₄⁺ to NO₂^-was slowed down, and the nitrogen transformation ability by N. europaea was reduced. Scanning electron microscopy (SEM) images showed that nanosilver heavily damaged the cell membrane by causing holes on the surface of bacteria. Transmission electron microscope (TEM) images showed that the nuclear material inside the bacteria was disappeared and the boundary of the cytoplasmic membrane was blurred. Flow cytometry (FCM) was employed to detect that nanosilver could generate intracellular reactive oxygen (ROS) in the cells. qRT-PCR technology was used to determine the expression of amoA, hao and merA of N. europaea after the exposure to nanosilver, and it was found that nanosilver inhibited the expression of the functional genes. In conclusion, nanosilver could interact with cell membrane, generated oxidative stress damage and inhibited the expression of functional genes amoA and merA of N. europaea, which further affected the transformation process of ammonium nitrogen. In addition, the toxicity of nanosilver with small particle size was stronger than that of large particle size.