Enantioselective Biodegradation Of The Chiral Insecticides Isocarbophos And Profenofos By Cupriavidus Nantongensis X1~t

Isocarbophos and profenofos are chiral organophosphorus insecticide and acaricide.They mainly control thrips,rice leaf rollers,prodenia litura in rice and cotton through contact and stomach poisoning.Due to the frequent application of isocarbophos and profenofos,their residual pollution in the environment and human health risks have attracted increasing attention.However,the toxicit of the chiral enantiomer is selective.Researchs have shown that S-isocarbophos and R-profenofos have the main insecticidal activity,while R-isocarbophos and S-profenofos are highly toxic to mammals.Bioremediation was the mainly pathway of environmental restoration.In this study,a bacterial strain of Cupriavidus nantongensis X1^T,which efficiently degrades different chiral enantiomers of isocarbophos and profenofos.This study analyzed their degradation characteristic,metabolic pathway,and degradation mechanism.It provides a theoretical basis for the environmental restoration of chiral pesticides.The main research results are as follows:1.Strain X1^T can preferentially degrade R-isocarbophos and S-profenofos.The optimal degradation conditions of R-isocarbophos by strain X1^Tin mineral salt medium is 37°C,p H 7-8 and 10%.Strain X1^T can degrade 97.4%of 12.5 mg/L R-isocarbophos within 1 h in the optimum conditions.As the concentration increases,the degradation rate of strain X1^T becomes slower and slower,and ability of degradation gradually becomes weaker.Taking dd water as a reference standard,in a 5mmol/L metal ion solution,Ni²⁺?Co²⁺?Mn²⁺?Mg²⁺?Ca²⁺?K⁺?Na⁺can promot the degradation of the R-isocarbophos by strain X1^T,while Cr³⁺?Al³⁺?Fe³⁺have an inhibitory effect on the degradation.2.UPLC and UPLC-MS/MS were used to determine the metabolites in the degradation process of isocarbophos.The results show that the degradation rate of isocarbophos under an alkaline condition is significantly faster than that under acidic and neutral conditions,because an alkaline condition promoted the hydrolysis of P-O or P-S bonds.However,isocarbophos was preferentially degraded to break the ester bond(C-O)rather than the P-O bond under alkaline condition,So a new chiral compound 2-((amino(methoxy)phosphorothioate)oxy)sodium benzoate(AMPOBA)was produced,which can be further degraded and eventually mineralized.By using ECOSAR(a tool for analyzing toxicity of pollutants to aquatic life)software,simulation analysis of the toxicity of isocarbophos and its metabolites.AMPOBA,a main metabolite under alkaline conditions,was much less toxic to fish and green algae than the metabolite isopropyl salicylate under neutral or acidic conditions.Therefore metabolite in an alkaline environment is safer for non-target organisms.3.In a mixed system of equal molar concentration of isocarbophos and profenofos,strain X1^T preferentially degrades R-isocarbophos,followed by S-profenofos,S-isocarbophos,and finally R-profenofos.In the same period of time,the separated degradation rate is always greater than the mixed degradation rate.Mixed degradation can weaken the degradation ability of strain X1^T.4.Continuous addition experiments have found that the degradation of S-isocarbophos is related to the concentration ratio of the two enantiomers in the degradation system.When EF_R<0.019,the two enantiomers of isocarbophos are degraded at the same time.The profenofos degradation experiment found that the degradation of R-profenofos is also related to the ratio of the two enantiomers in the degradation system.When EF_S<0.27,the strain X1^T can simultaneously degrade the two chiral enantiomers of profenofos;When EF_S>0.27,only S-profenofos can be degraded.