| With the rapid development and wide application of nanotechnology and nanomaterials in human life, the scientific community and environmentalists pay more attention to safety problems in nanomaterials. During its production and usage, a large number of nanoparticles get into animals and plants through the air, water and soil, which brought the potential impact to environment and ecological system. At present, many reports about the toxicity of nanomaterials research more focused on mice or in vitro cultured cells, but neglected the environment, especially aquatic organisms.Protozoan is a kind of single-cell organism, which has advantages of easy collection, rapid propagation, large cell volume, convenient operation and observation. Also, it plays an essential role on aquatic ecosystems and has an effect on nutrient cycle and energy flow. Therefore, protozoan is commonly as a research material to study toxicology. The influence of the Euplotes aediculatus structure in response to different concentration of 50 nm sized triangle plate shaped silver nanoparticles (SNPs) was visualized by using methylthiazoletetrazolium colorimetric assay (MTT), differential interference contrast microscopy (DIC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which was expected to provide experimental basis for the exploration of the cytotoxicity and toxicity mechanism of nanomaterials, scientific evidence for the biological toxicity evaluation system, environmental risk assessment and nanomaterials prediction, and the new data for the toxicity study of the aquatic species.1. The influence of SNPs on the cytotoxicity of ciliate E. aediculatusMTT is a routine cell viability assay in the study of cytotoxicity of SNPs. The influence of the cell proliferation, morphological and behavioral changes in response to different time and concentration of 50 nm sized triangle plate shaped SNPs was visualized by using MTT and DIC.The inhibition ratio on the growth of cell showed a trend of significant linear with the increase of the SNPs. However, the change of cell growth is nonlinear with treatment time. The results show that with the prolong of treatment time, the inhibition of the cells treated in the same concentration of SNPs decreased slightly. Besides, the median lethal concentration (LC50 value) was obtained by means of probit method, and the LC50,4 h of SNPs medium on E. aediculatus were 0.94 mg/L. Observation of E. aediculatus showed that the treated cell moved slowly, the morphology of cells changed obviously, such as, the length and width decreasing significantly, body shape changing from normal oval to spindle or even flat-spherical. The peak of the length-width ratio shifted gradually from the normal range of 1.7-2.2 to 1.3-1.7, and the finally length-width ratio of the cells tended to be 0.9-1.3. So in vivo observation also confirms that E. aediculatus is more sensitive to the toxicity of SNPs. In addition, the change of cellular morphology also effect on the growth of cell to some extent as well.2. The influence of SNPs on the ultrastructure of ciliate E. aediculatusThe influence of the ultrastructure of E. aediculatus in response to different concentration of 50 nm sized triangle plate shaped SNPs were visualized by SEM and TEM. The results show that most of the ciliary shafts of membranelles in the collar region and lapel region and frontal-ventral-transverse cirri ruptured sequentially, and kinetosomes of certain frontal-ventral-transverse cirri were also bared or desquamated; under the oral cortex, the lack of mitochondrial crista gradually aggravated from inside to outside, and under the pellicle, mitochondria swelled dramatically; with the nucleolus and chromatin gathering, the macronucleus membrane gradually became blurred, and holes appeared on the part of the chromatin mass; a large number of autophagic lysosomes and the medullary structures formed in the cytoplasm. In addition, SNPs were observed in cell membrane, cytoplasm, mitochondria membrane and its interior. According to available data, it is speculated that SNPs can invade the cell membrane besides of cytostome, and mainly by damaging the mitochondrial and macronucleus the toxicity can causes damages of other organelles which leads to cell morphology and functional disorders. And analysis of the characteristics of cell death revealed that the death way of cell treated with SNPs was a special cell death mode between autophagy and oncosis. |
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