摘要:
为了探讨AgNPs对典型微藻的急性毒性效应及其机制，采用柠檬酸钠还原法制备AgNPs，以摇瓶实验法评估了不同浓度的AgNPs和Ag+对铜绿微囊藻和普通小球藻叶绿素a含量、形态结构和叶绿素荧光参数的影响。实验结果表明：AgNPs对普通小球藻和铜绿微囊藻的96 h-EC50分别为1.113 mg·L-1和0.697 mg·L-1，而Ag+对2种藻的96 h-EC50分别为0.106 mg·L-1和0.032 mg·L-1。扫描电镜结果表明：AgNPs处理使普通小球藻细胞表面出现褶皱，细胞变形甚至向内塌陷。对铜绿微囊藻部分细胞出现变形变得不规则，且出现某些胞外物质使细胞粘附在一起。透射电镜观察发现，高浓度Ag+处理使2种藻的细胞均发生质壁分离，部分细胞转变为孢子。而AgNPs处理使普通小球藻细胞蛋白核增大，蛋白核与类囊体区无明显连接通道。铜绿微囊藻拟核区膨大，类囊体和色素体被推向四周，部分类囊体断裂，同时，发现该藻可以分泌胞外物质在细胞周围吸附AgNPs颗粒。对于普通小球藻，0.6 mg·L-1 AgNPs处理后细胞光系统Ⅱ的最大光化学量子产率φP0相对于CK没有显著差异，但0.09 mg·L-1 Ag+处理使φP0显著增加。在高浓度AgNPs或Ag+处理时，φP0均显著降低。AgNPs未对普通小球藻光系统II性能参数PI_Abs造成影响，但不同浓度Ag+处理均使得该参数显著升高。对于铜绿微囊藻，2种毒物均使其φP0显著降低。而PI_Abs仅在2种毒物的最高浓度处理时显著降低。综上，AgNPs对2种藻的急性毒性远小于Ag+，而两者对铜绿微囊藻的毒性均大于普通小球藻。AgNPs胁迫使2种藻叶绿素a含量显著降低，并诱导2种藻在形态结构和光合生理方面发生了显著变化，造成不同程度的损伤，但与Ag+的毒性效应存在一定的差异。提高光吸收能通量补偿耗散能量和分泌胞外物质结合Ag+是微藻2种重要的解毒机制。
Abstract:
To investigate the effects of silver nanoparticles (AgNPs) on microalgae and its mechanism, batch experiments were conducted to examine the acute effects of AgNPs and silver ion (Ag+) on chlorophyll a content, cell morphology and chlorophyll fluorescence parameters of Chlorella vulgaris and Microcystis aeruginosa. The results showed that the 96 h-EC50 of AgNPs on two algae were 1.113 mg·L-1 and 0.697 mg·L-1, while for Ag+ 0.106 mg·L-1 and 0.032 mg·L-1, respectively. Scanning electron microscopy results showed that the AgNPs treatment induced cell surface drape, cell deformation or even collapse inwards in C. vulgaris cells. For M. aeruginosa, some algal cells became irregular, and extracellular material made cells stick together. Moreover, according to transmission electron microscope results, plasmolysis showed in cells of both algae and some algal cells have turn into spores with the high concentration of Ag+ treatment. In addition, the pyrenoid of C. vulgaris enlarged and the channel between nuclear and thylakoid protein area disappeared in treatment with high concentration of AgNPs. It is showed that in M. aeruginosa cells the nucleus region enlarged, the thylakoid and plastid pushed around, and some thylakoids fractured. There was no difference showed in the maximum quantum yield of primary photochemistry (φP0) of C. vulgaris cells between the treatment with 0.6 mg·L-1 AgNPs and CK, while there was a significant difference in φP0 between CK and the treatment with 0.09 mg·L-1 Ag+. Moreover, significant reduction in φP0 showed in treatments with high concentration of AgNPs or Ag+ compared with CK. The performance index of PSII on absorption basis (PI_Abs) of C. vulgaris cells treated with Ag+ was always greater than that of CK, while there was no significant difference among all the treatments with AgNPs. For M. aeruginosa, the values of φP0 were significantly lower in all treatments with AgNPs or Ag+ than that in CK. However, only at the highest concentrations of AgNPs and Ag+ exposure, there was significant reduction in values of PI_Abs. In conclusion, the acute toxicity of AgNPs on both algae were lower than that of Ag+, while the toxicity of AgNPs and Ag+ on M. aeruginosa was greater than that on C. vulgaris. Promoting the light absorption energy flux to compensate energy dissipation and releasing extracellular materials to complex with Ag+ could be two important deintoxication mechanisms.
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