Study On The Response Of Mixed Trophic Brown Flagellates To Heavy Metal Cadmium Stress And Its Enrichment Ability

Factors such as human activities and changes in the natural environment have led to the aggravation of heavy metal pollution and further deterioration of water quality and environment,which has seriously threatened the safety of drinking water and aquaculture water and aquatic products and become an urgent water environmental problem.Cadmium(Cd)is one of the main man-made pollutants in the aquatic ecosystem,which has affected the aquaculture water in China,and its residues have been detected in many kinds of aquatic animals.Protozoa can absorb and transport certain heavy metals and have become important organisms in water environment monitoring and prevention and control of heavy metal pollution.Taking protozoan Ochromonas gloeopara as the research species,this thesis studied the response of O.gloeopara to the increase of Cd concentration under autotrophic and mixotrophic conditions,and further studied the removal effect of different concentrations of Cd,and on this basis,how the fluctuation of nutrient concentration affected the Cd removal ability of O.gloeopara.Finally,the transcriptome changes of O.gloeopara under Cd stress were analyzed.The main conclusions of this paper are as follows:(1)The response of photoautotrophic O.gloeopara to Cd stress and its Cd removal ability under different nitrogen and phosphorus concentrations.In this study,photoautotrophic O.gloeopara were used to study their growth and photosynthetic response to Cd,with special attention to the effects of initial Cd concentration and nitrogen and phosphorus concentration on Cd removal capacity.The results showed that the growth rate and Cd removal ability of O.gloeopara were significantly inhibited when the concentration of Cd reached 0.5 mg L^-1,while the photosynthesis decreased significantly when the concentration of Cd reached 0.15 mg L^-1.In addition,when the Cd concentration was 0.15,0.5,0.9,1.6,and 2.0 mg L^-1,the removal efficiency of Cd by O.gloeopara was 83.2%,77.7%,74.6%,70.1%and 68.8%,respectively.The increase of nitrogen has no obvious effect on the Cd-removing ability of O.gloeopara,but the increase of phosphorus concentration significantly improves its Cd-removing ability.The above results show that the photoautotrophic O.gloeopara have strong tolerance and removal ability to Cd,and increasing the concentration of phosphorus can improve its removal ability,which indicates that O.gloeopara have great potential application value in reducing Cd pollution in water.(2)Growth and photosynthesis response of O.gloeopara to Cd stress and its ability to remove Cd under mixotrophic conditionsThere is a lot of organic matter that can be used by protozoa in the field water environment,and the use of organic matter can increase the biomass of protozoa.Therefore,this study used continuous addition of glucose at the concentration of 100mg L^-1as organic matter to study the photosynthesis of O.gloeopara under mixotrophic and the growth response to different concentrations of Cd stress,and focused on whether the addition of organic matter could improve the ability of O.gloeopara to remove Cd.First,set six Cd concentrations of 0,0.2,0.6,1.0,1.9 and 2.4 mg L^-1,and the initial O.gloeopara concentration was set to 5×10⁴ cells m L^-1.Glucose was added every 12 hours in the experiment to make the glucose concentration in the experimental100 mg L^-1 to ensure that the O.gloeopara were always in a mixotrophic state.The experimental results show that the addition of glucose can significantly improve the resistance of O.gloeopara to Cd toxicity,thus enhancing the ability of the O.gloeopara to remove Cd.O.gloeopara can remove 93.8%,92.1%,90.1%,76.4.1%and 69.2%of Cd.(3)Transcriptome analysis of tolerance to Cd toxicity of O.gloeopara under mixotrophicBased on the fact that the O.gloeopara can tolerate and eliminate the heavy metal Cd in this paper,transcriptome technology was used to compare the transcriptome test results of the O.gloeopara without Cd stress and with a concentration of 1.0 mg L^-1 Cd,and to analyze the molecular mechanism of Cd tolerance and removal in O.gloeopara.The experimental data indicated that differentially expressed genes are mainly related to transportation and anti-oxidative stress.The results of this study proved that O.gloeopara show high absorption and high tolerance to Cd,which are related to the various heavy metal transport proteins contained in their bodies and functional genes of antioxidant stress.In summary,O.gloeopara can tolerate higher concentrations of Cd stress and can remove Cd;changes in phosphorus concentration can affect their removal of Cd;continuous addition of glucose can improve the tolerance and removing ability of O.gloeopara to Cd;through the transcriptome analysis of O.gloeopara,it is revealed that the tolerance of the O.gloeopara to Cd under mixotrophic is related to the multiple heavy metal transporters contained in the body and the functional genes of antioxidant stress.