| The problem of heavy metal pollutions is one of the hottest spots in recent researches. The biodegradation and bioaccumulation by microbes in the treatments of heavy metals has been confirmed. However, the use of protoza (e.g. Tetmemena pustulata) to accumulate heavy metals has not been largely reported. On the one hand,the biological indexes of the protozoa can be used as indicators in the detection of environmental, on the other hand, the bioaccumulation of heavy metals of protozoa can help to relieve the heavy metal pollutions. This study is aimed to select a tolerant species of protozoa,so as to provide new ideas for the bioremediation of water pollution.In this paper,the experiments were carried out from the following four aspects and the experimental results were exhibited as bellow:1. The toxic Microcystis aeruginosa (PCC 7806) was supplied as the sole food source to simulate the environmental stress condition to screen out a certain tolerant species. The water drawed from wild ponds was added by M aeruginosa and cultured for several generations. The dominant species of protozoa was selected. Accrodding to the morphological characteristics and the SSU rRNA gene sequence, the dominant protozoa was identified as Tetmemena pustulata. When explored to different food resources, it turned out that 0.1% yeast, 1% glucose and 0.1% barley water could be used as the food resources of T. pustulata, but T. putulata showed different growth capacity in different food resources. When the yeast was the sole food, the population of T. pustulata can maintain in the level of environmental capacity, the decline stage delayed. When the glucose and the barley water were supplied as food, the environmental capacity were lower than fed by yeast and the population decline stage were advanced. Yeast powder is considered to be the ideal food for T. pustulata. The population of T. pustulata could grow stably and the decline stage is delayed.2. The acute toxicity test revealed the tolerance of T. pustulata to some heavy metals. The 24h acute toxicity test revealed that the median lethal concentrations(LD50) of copper, zinc, chromium and cadmium to T. pustulata were 126.1 ?g/L,28.26 mg/L, 4.57 mg/L and 7.03 mg/L, respctively. The order of toxicity of these four heavy metals to T. pustulata was generally: Cu2+> Cr6+> Cd2+> Zn2+. The 48h acute toxicity test revealed that the LD50 of copper, zinc, chromium and cadmium to T.pustulata were 53.46 ?g/L, 23.28 mg/L,4.19 mg/L and 2.52 mg/L, the order of toxicity was generally: Cu2+> Cd2+> Cr6+> Zn2+. The toxicity of cadmium was stronger than chromium in 48h. The 72h acute toxicity test revealed that the LD50 of copper?zinc?chromium and cadmium to T. pustulata were 43.55 ?g/L, 21.53 mg/L,4.02 mg/L and 1.43 mg/L, the order of toxicity was generally: Cu2+> Cd2+> Cr6+>Zn2+. The 96h acute toxicity test revealed that the LD50 of copper, zinc, chromium and cadmium to T. pustulata were 41.63 ?g/L, 19.37 mg/L, 3.94 mg/L and 0.95 mg/L, the order of toxicity was generally: Cu2+> Cd2+> Cr6+> Zn2+. The results showed that the effective lethal concentrations of these four heavy metals showed a downward trend with the extension of exposure time. Copper was the most toxic heavy metals,followed by cadmium and chromium, zinc is the weakest.3. The chronic toxicity test analyzed the effect of heavy metals on the cell division and the antioxidant enzyme activities of T. pustulata. The results showed that when the concentration of copper was 5 to 10 ?g/L, the cell division of T. pustulata was promoted, and the time to first division was shortened. When the concentration of copper was 15 to 30 ?g/L,the cell division of T. pustulata inactive was inhibited, and the time to first division was delayed. When the concentration of copper exceeds 30?g/L, the cell division of T. pustulata stopped. When the concentration of zinc reached to 5 mg/L, the cell division of T. pustulata was promoted, and the time to first division was shortened. When the concentration of zinc was 10 to 20 mg/L, the cell division of T. pustulata was inhibited, and the time to first division was delayed. When the concentration of zinc exceeded 20 mg/L, T. pustulata stopped divising. Under the exposure to cadmium and chromium, the result showed that the cell division was inhibited and the time to first division was delayed. When the concentration of cadmium exceeded 0.7 mg/L, it makes T. pustulata stop divising. And the concentration of chromium exceeds 2.0 mg/L, it makes T. pustulata stop divising. The antioxidant enzyme activity T. pustulata has been showed that under the low concentrations of heavy metals the activities of antioxidant enzymes were promoted to protect the organisms from the damage of free radicals, but high concentrations of heavy metals will then destroy the antioxidant system, therefore stop the cell division,even cause death.4. Accroding to the bioaccumulation experiments, the potential use of T.pustulata in decontamination industrial wastewater is possible. In this study,chromium and zinc were chosen to analyze the possibility of T. pustulata in decontamination. The result showed that T. pustulata can bioaccumulate the environment metals (Zn2 + and Cr6+ ) It turned out that the concentration of Zn2+decreased by 78.2%, and the concentration of Cr6+ decreased by 63.2% after 24-hour-accumulation by T. pustulata. The concentration of Zn2+ decreased by 89.8%, and the concentration of Cr6+ decreased by 69.5% after 48-hour- accumulation by T. pustulata.After 72 hours the concentration of Zn2+ in the environment decreased by 91.8%, and the concentration of Cr6+ decreased by 74.7%. After 96 hours the concentration of Zn2+ in the environment decreased by 93.2%, and the concentration of Cr6+ decreased by 75.8%. Therefore, the apply of T. pustulata to bioaccumulate the aquatic environmental heavy metal is assumed to be possible... |
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