Study On The Toxic Effects And Mechanisms On Bacillus Subtilis Induced By Perfluorooctane Sulfonate

Perfluorinated compounds(PFCs)are widely used in industrial products and daily products,while perfluorooctane sulfonic acid(PFOS)is considered as degradation products of PFCs.Due to incomplete or ineffective treatment,PFOS enters soil environment through waste water and dust discharge,landfill and usage of fertilizers and pesticides.A significant level of PFOS exists in soil,which is environmental persistent,bioaccumulative and biotoxic.At present,investigations on distribution,migration,transformation and toxicity of PFOS are mainly about animal tissues,blood and aquatic organisms,while the study on toxicity of PFOS on bacteria is still limited.The effect of organic compounds and heavy metals coexisting with PFOS on PFOS bacterial toxicity has not been clarified.Cr(VI)and PFOS coexist in the chromium plating wastewater and are discharged into environment due to the incomplete removal.Moreover,the chromium pollution in environment is widespread.However,the ecological risks caused by the coexistence of PFOS and Cr(VI)haven't gained enough attention.PFOS is an amphiphilic organic substance.The interactions between organic matters(such as humic acid and protein)and PFOS may affect the toxic effects of PFOS and the response of bacteria to its stress.?-amylase is one of the metabolites of Bacillus subtilis,and it is also an important starch hydrolyzing enzyme,which is widely presented in animals and plants,microorganisms,sludge and soil.It is beneficial to the degradation and utilization rate of organic matters by microorganisms.It can hydrolyze the extracellular polymer substances produced by microorganisms,which can affect the flocculation and film formation of microorganisms,thereby increasing the susceptibility of microorganisms to toxic substances.Most importantly,it can also provide binding sites for pollutants and reduce the bioavailability of pollutants.Thus,it is meaningful to study the effect of ?-amylase on the combined toxicity of PFOS or/and Cr(VI)on bacteria and bacteria response to PFOS stress.Firstly,this paper studied the combined toxic effect and mechanism of PFOS and Cr(?)on bacteria,in order to analyze the difference between the combined exposure of two pollutants and single pollutant exposure,which provides references for accurate assessment of PFOS ecological risk.Secondly,?-amylase that is widely presented in soil is chosen as model organic matter to study the effect of its presence on combined toxicity of PFOS and Cr(?)on bacteria,and the response of bacteria to PFOS.Part 1:The study of the single toxicity of PFOS and the combined toxicity of PFOS and Cr(?).Firstly,monitor the growth of bacteria and draw a growth curve to characterize the growth toxicity of PFOS,PFOS and Cr(?)to bacteria.Secondly,the cell membrane permeability,hydrophobicity and bacterial surface morphology were measured by fluorescent probe method,contact angle and scanning electron microscope to characterize the influence of PFOS,PFOS and Cr(?)on the cell membrane properties.Then redox indicators(active oxygen content,superoxide dismutase and catalase activity)were measured to analyze the effects of PFOS,PFOS and Cr(?)on the bacterial redox system.Analyze the composition and content of extracellular polymers(EPSs)using three-dimensional fluorescence technology and colorimetry.Results showed that the toxicity of PFOS to bacteria is dose-dependent,and the presence of Cr(?)reduces the toxicity of PFOS to bacteria.PFOS without or with Cr(VT)exposure mainly cause cytotoxicity by interfering with cell metabolism,inducing cell membrane damage and oxidative stress.The second part:studying the role of ?-amylase in the response of Bacillus subtilis to PFOS exposure.Molecular simulation was used to analyze the interaction between ?-amylase/sortase A and PFOS.In addition to some experiments using the same experimental methods as the first part,the measurement of zeta potential,Fourier infrared spectroscopy and high performance liquid chromatography were also used to explore the effects of ?-amylase on cell membrane properties,redox and cell metabolism.The results show that the competitive adsorption of PFOS by ?-amylase and sortase A can reduce the bioavailability of PFOS and promote the metabolic adaptation of bacteria to PFOS.?-amylase can reduce the toxicity of PFOS to bacterial growth,membrane permeability and oxidative damage,and can affect a series of complex metabolic reactions such as the production of metabolic signal molecules(acetic acid)and the surface properties of bacteria.To study the effect and mechanism of ?-amylase on the combined toxicity of PFOS and Cr(?)to bacteria.CCK-8 was used to detect the activity of bacteria,and spectroscopy techniques were used to measure cell membranes properties,redox system,and the production of extracellular polymers in order to study the effects of?-amylase on the combined toxicity of PFOS and Cr(?)to bacteria.Results show that the addition of ?-amylase can enhance the combined toxicity of PFOS and Cr(?)to bacteria.The results of this study clarify the toxic effects and possible mechanisms of PFOS and Cr(?)on Bacillus subtilis,and analyze the role of ?-amylase in the response of Bacillus subtilis to PFOS and Cr(?)exposure.