Study On Degradation Of Chlorophenols By Cupriavidus Nantongensis X1~T And 2,4,6-trichlorophenol-4-monooxygenase

Chlorophenols（CPs）,as important chemical raw materials and organic intermediates,are widely used in industrial and agricultural development and human production activities.However,due to long-term large-scale use and non-standard emissions,they have caused serious environmental pollution,endangering human health and ecological safety,and are typical persistent organic pollutants in the environment.The microbial remediation method has the advantages of low investment cost,thorough treatment and no secondary pollution,and is considered to be the most potential pollution remediation method.In this paper,the degradation performance of Cupriavidus nantongensis X1^Tstrain on CPs was studied,the degradation characteristics of 2,4,6-trichlorophenol-4- monooxygenase（Tcp A）on CPs and their structural analogues were studied,and the metabolic pathway and mechanism of Tcp A catalytic degradation of CPs and their structural analogues were discussed.The main results are as follows:1.The degradation results of strain X1^Ton a variety of typical CPs show that:Strain X1^Thas a good degradation effect on CPs,which can completely degrade MCPs or2,4-DCP with an initial concentration of 20 mg/L within 6 hours,and the degradation effect decreased with the increase of the number of chlorine substituted on benzene ring.Strain X1^Tcan grow with 2,4-DCP as the sole carbon source and energy source,which can degrade not only 2,4-DCP but also metabolites of 2,4-DCP.2.The degradation kinetics of MCPs and DCPs by Tcp A showed that:Under aerobic condition,the degradation process of MCPs and DCPs by Tcp A conforms to the first-order kinetic reaction model.The initial concentration of substrate can affect the degradation effect of Tcp A,it can reduce the degradation activity of Tcp A.The position of the chlorine substituent on the benzene ring of CPs can affect the degradation effect of Tcp A,and the order of degradation rate of MCPs by Tcp A is:K_2-CP>K_3-CP>K_4-CP.The order of degradation rate of Tcp A to DCPs with initial concentration of 10 mg/L is:K2,4-DCP>K2,5-DCP>K2,3-DCP>K3,5-DCP>K3,4-DCP>K2,6-DCP.3.The degradation kinetics of 4-CP,2,4-DCP and their structural analogues by Tcp A showed that:The ability of Tcp A to catalyze the oxidation of CPs was positively correlated with the electron-withdrawing ability of the group at para-position on the benzene ring.The stronger the electron-withdrawing ability of the group at para-position,the easier the oxidation reaction will take place.Tcp A has the dual function of degrading halogenated phenol and nitrophenol,and has a broad spectrum of degradation substrates.4.The metabolic products and pathways of Tcp A to MCPs,DCPs and their structural analogues were analyzed.The mechanism of gradual dechlorination of CPs catalyzed by Tcp A under aerobic condition was discussed:Regardless of whether the para-position group on the benzene ring of the CPs is-Cl or-H,the first step of the Tcp A catalytic degradation reaction is to undergo an oxidation reaction at the para-position on the benzene ring to generate a p-benzoquinone structure compound.If the ortho-position of the compound is-Cl,then it will be hydrolyzed by Tcp A at the original binding site to remove the ortho-position;If the ortho-position of the compound is-H,it cannot be further catalytic degradation.The compounds of p-benzoquinone structure are finally reduced by excessive NADH or other reducing substances in the reaction system to generate compounds of hydroquinone structure.If there are two or more-Cl on the benzene ring of the p-benzoquinone structure compound,the electron cloud density on the benzene ring will be lower and relatively stable,and it cannot be further degraded by catalytic dechlorination degradation.