Biodegradation Of Six Organophosphorus Insecticides By Cupriavidus Nantongensis X1~T

Organophosphorus pesticides(OPs)as one of the most widely used pesticides in the world greatly contribute to increasing agricultural product.However,the abundant usage of OPs has caused severe ecological and environmental problems,threatening human health.Hence,it is urgent to enhance the degradation of OPs in the environment and to remediate the contaminated environment.Microbial remediation is recognized as an economic,efficient,and environmental friendly remediation strategy,with no further contamination,hence is with high potential for practical application.In this study we investigated the degradation capability of a chlorpyrifos degrading strain,Cupriavidus nantongensis X1T,for six widely used OPs,with further discussion.on the degradation pathway of these six OPs.Main conclusions are as following:1.The single factor experimental method,was used to reveal the optimal conditions for chlorpyrifos degradation.Results show that:(1)The optimal temperature,pH,optimal amount of application are 37?,7-9,and 10%,respectively.(2)The degradation efficiency of the bacteria X1T for chlorpyrifos within 12 hours are 100%,100%,92.8%,46.2%and 39.1%,with an initial chlorpyrifos concentration of 5,50,100,500 and 1000 mg/L,respectively.The results indicate that this bacteria strain can tolerant chlorpyrifos concentrations as high as 1000 mg/L.(3)The crude enzyme had degrading activity for chlorpyrifos,yet with lower activity than the living cells with an equivalent amount of bacteria.2.The bacteria X1T has a broad spectrum for substrate degradation,with high degradation efficiency for parathion-methyl,parathion,fenitrothion triazophos,phoxim 3,5,6-trichloro-2-pyridinol,p-nitrophenol,2-chloro-4-bromophenol,2,4-dichlorophenol and phenol.3.The degradation kinetics of X1T for six representative OPs(parathion-methyl,triazophos,chlorpyrifos,phoxim,isocarbophos and profenofos)showed than(1)the degradation process conformed to the first-order kinetics equation Ct=Coe-kt;(2)The degradation of X1T for parathion-methyl,triazophos,phoxim(50mg/L)was most efficient,with half-life being 8.5min,9.4min,and 44.6min,respectively.The degradation half-life of X1T for chlorpyrifos,isocarbophos and profenofos was 3.3h,10.2h,and 34.7 h,respectively.4.The investigation of X1T for profenofos and isocarbophos at the enantiomer level showed that:(1)the degradation of X1T for these two OPs had significant enantiomer selectivity,with a significantly higher degradation efficiency of(+)-profenofos and R(-)-isocarbophos than that of(-)-profenofos and S(+)-isocarbophos,respectively.(2)The degradation half-life of X1T for Rac-isocarbophos(50mg/L)was 10.2 h,and within 2 hours the R(-)-isocarbophos was nearly 100%degraded,namely with a half-life of 0.3 h;while S(+)-isocarbophos was hardly degraded within 2 hours,with a ES value of 1,indicating that the degradation of isocarbophos by X1T has absolute selectivity before the degradation of R(-)-isocarbophos was completed.5.In this study we analyzed the metabolic intermediates during the degradation of parathion-methyl,triazophos,chlorpyrifos,phoxim,isocarbophos and profenofos by X1T.And the degradation pathways of these six OPs were speculated.Results indicated that these OPs were primarily hydrolyzed with the role of hydrolases into phenols,which were further accumulated or stepwise oxidized(dehalogenated)afterwards with the role of 2,4,6-trichlorophenol monooxygenase,finally following by the cracking of benzene rings and pyridine rings and the final mineralization.In conclusion,our study revealed that the bacteria strain X1T has high degradation efficiency and a broad spectrum for the degradation of several OPs and phenols.The degradation mechanism of OPs by X1T was that:the OPH(Organophosphorus Hydrolase)catalyzed the hydrolysis of phosphoester bond of the OPs.And the produced phenols were stepwise oxidized with the role of 2,4,6-trichlorophenol monooxygenase,finally following by the cracking of benzene rings and pyridine rings and the final mineralization.This study is with practical and theoretical significance for utilizing the X1T strain for the OPs contamination remediation in the environment.