氧化石墨烯对淡水微藻生长及生物活性物质的影响

Effects of graphene oxide on the growth and bioactive compounds in freshwater microalgae

为掌握氧化石墨烯(GO)的水环境风险,以斜生栅藻(Scenedesmus obliquus)和湖泊微拟球藻(Nannochloropsis limnetica)为研究对象,探究了GO对淡水微藻生长及其生物活性物质(碳水化合物、总蛋白质、总脂)的影响.结果表明,GO对2种微藻具有中等毒性,72h EC50值分别为25.63和48.44mg/L.透射电镜(TEM)观察发现,GO纳米片层既能附着于藻细胞表面也能进入藻细胞内部,造成藻细胞超微结构明显变化,包括:质壁分离;叶绿体收缩;淀粉粒数量减少甚至消失.较低浓度(10mg/L)GO会促进微藻中光合色素(叶绿素a、叶绿素b、类胡萝卜素)合成;而较高浓度(100mg/L)GO暴露下,2种微藻的类胡萝卜素和斜生栅藻叶绿素a的含量显著降低.2种浓度的GO总体上刺激了藻细胞内生物活性物质的合成,这是污染胁迫下的一种主动防御机制;而较高浓度GO造成碳水化合物含量显著降低,可能原因是细胞中储能物质由淀粉向中性脂转化.

To understand the risk of graphene oxide(GO)to aquatic environments,the effects of GO on the growth and three bioactive compounds including carbohydrate,total protein and total lipid,in two species of freshwater microalgae,Scenedesmus obliquus and Nannochloropsis limnetica,were investigated in this study.Results showed a moderate toxicity of GO to both species with the 72h EC50 values of 25.63mg/L and 48.44mg/L,respectively.Transmission electron microscopy(TEM)images displayed that GO nanosheets not only adhered to the cell surfaces but also entered the cells,which induced obvious changes in ultrastructure,including plasmolysis,shrinkage of chloroplasts,and the decrease or even disappearance of starch grains.Synthesis of three photosynthetic pigments(chlorophyll a,chlorophyll b and carotenoid)in microalgae was promoted at lower concentration(10mg/L)of GO after 72h exposure.However,contents of carotenoid in the cultures of both species and chlorophyll a in the culture of S.obliquus decreased significantly when exposed to the higher concentration(100mg/L)of GO.Basically,the synthesis of three bioactive substances in algal cells was stimulated under both experimental concentrations of GO,implying an active defense mechanism under stress.The decrease of carbohydrate content in cells of S.obliquus exposed to 100mg/L GO was hypothesized as results of the conversion of energy storage materials,i.e.from starch to neutral lipids.