Toxic Effect And Toxic Mechanism Of Bacteria Induced By PFOS Combined With Chromium Or Aluminum Pollution

Since their excellent physical and chemical properties,perfluoroalkyl compounds(PFASs)are widely used in various aspects of industry,agriculture and life.However,due to the incomplete treatment,PFASs exist widely in the environment,soil is an important destination for PFASs.Perfluorooctane sulfonic acid(PFOS)is an intermediate product of many PFASs that is difficult to be further degraded.Therefore,great attention has been paid to the soil ecological risks and hazards caused by PFOS.However,the ecological risk and bacterial toxicity of soil acidification to PFOS have not yet been clarified,and the joint ecological toxicity of PFOS and other typical pollutants(chromium and aluminum)in soil under acidic conditions should be paid more attention.Chromium pollution in soil and aluminum leaching caused by soil acidification may affect the ecological risks and hazards induced by PFOS.Therefore,in the background of soil acidification,this thesis took the functional model microorganism Bacillus subtilis as the research object,carried out the study of the combined toxicity effect and mechanism of PFOS and Cr(?)/Al on bacteria,and studied the effect of PFOS+Cr(?)/Al on bacterial growth and metabolism.The specific research results are as follows.The first part:Effect of PFOS on toxicity of Bacillus subtilis induced by Cr(?).The results of the study show that compared with Cr(?)alone,PFOS+Cr(?)is more toxic to bacteria.Compared with the biological activity of bacteria exposed to Cr(?)alone and the control bacteria,the biological activity of bacteria exposed to PFOS+Cr(?)was reduced by 18%and 56%,respectively,which indicated that PFOS increases the toxicity of Cr(?)to Bacillus subtilis.In addition,the properties and components of the extracellular polymer of Bacillus subtilis have changed,such as a decrease in potential,an increase in extracellular polysaccharides,a decrease in extracellular proteins,and irregular morphology,which also confirmed that PFOS increases the toxicity of Cr(?)to the bacteria.Oxidative damage and increased membrane permeability are the main toxic mechanisms.The second part:Under the condition of soil acidification,the study of PFOS+Cr(?)on the growth and metabolic toxicity of Bacillus subtilis.The results of the study showed that under the acidic condition of pH=5,the inhibition rates of Cr(?)alone,PFOS alone and PFOS+Cr(?)on bacterial growth(24.3%,42.3%and 41.6%,respectively),the inhibition rate of bacterial growth is 2?3 times of that pH=7.Under acidic stress conditions,PFOS+Cr(?)greatly reduces the metabolic activity of bacteria.The metabolic activity indicators of bacteria(DHA and ETS)at pH=7 are 5?8 times and 2?13 times,respectively,of the activities at pH=5.The isoelectric point,surface hydrophobicity and molecular docking analysis of bacteria consistently show that under acidic conditions,the interaction of hydrogen bonds,hydrophobicity and static electricity enhances the interaction between bacteria and PFOS/Cr(?).The third part:Under the acidic conditions of pH 4.5 and 5,the study of the influence of PFOS+Al on the growth and material metabolism of Bacillus subtilis.The results of the study showed that,compared with the pH value of 5,the toxicity of PFOS+Al to Bacillus subtilis was significantly increased under the acidic stress of pH 4.5.PFOS+Al significantly inhibited the production of NH4+ and soluble protein.In addition,with the extension of the culture time,the decrease of tryptophan and tyrosine protein-like components in the bound extracellular polymer,the production of humus,and the large production of acetic acid indicate that bacteria regulate the pH of the system by regulating metabolism,and then affect the existence of PFOS+Al to adapt to the adverse environment.When the acidic stress increases,the toxicity of PFOS+Al increases,and the metabolic activity of bacteria is greatly reduced.This is due to the decrease of bacterial membrane potential(MP)and the increase of NPN absorption,causing membrane damage,affecting the normal growth of bacteria and cell metabolism,and ultimately leading to bacterial death.In summary,the joint toxicity of PFOS+Cr(?)/Al to bacteria increases in acidic soil.Therefore,in the treatment of soil ecology,we should not only to detoxify and restore pollutants,but also pay attention to the aggravation of toxicity caused by soil acidification.