| Iprodione is a kind of efficient broad-spectrum,contact antiseptic belonging to dicarboximide.It is used in the plantation of a variety of crops to control several pathogens,such as Botrytis cinerea,Monilia and Sclerotinia,and receives good effect.But the residues of iprodione in soil and crop bring the threat to the safety of food and human.Bioremediation based on the microbial degradation has received increasing attention,because it is as an efficient,safe and promising biotechnological approach to clean up iprodione residues in the environment.Currently,only 3 articles concerning the isolation of iprodione-degrading strains have been published,and these strains only degraded low concentration of iprodione(10 mg L-1)within 7 days.In addition,little information about the enzymatic and pathway aspects involved in the degradation of iprodione is available up to date.The main objective of this study is to isolate efficient iprodione-degrading strains,to investigate the degradation mechanisms against iprodione,and to provide strain resources and theoretical basis for bioremediation.The main results are as follows:1)A bacterial strain YJN-G capable of degrading iprodione was isolated from the activated sludge in the wastewater treatment system of a pesticide factory.According to its physiological&biochemical characters,and the similarity analysis of its 16S rRNA gene sequence,strain YJN-G was primarily identified as Microbacterium sp.Strain YJN-G could grow well under the condition of pH 6.0?9.0,the optimum temperature and pH for its growth was 30?37 ? and 7.0.Strain YJN-G was able to grow normally under the NaCl concentration lower than 30 g L-1.2)Strain YJN-G could use iprodione as the sole carbon source for its growth.With the inoculation amount of 5%,strain YJN-G was able to degrade 100 mg L-1 iprodione within 24 hours.The optimum temperature and pH for the degradation of iprodione was 30?37 ?and 7.0,respectively.The degradation efficiency increased positively with the increase of inoculation amount.With the addition of metal ions(2 mmol L-1),Ba2+ and Mn2+ had no significant influence on the degradation of iprodione,Ni2+ slightly inhibited the degradation with Cd2+,while Cu2+ and Hg2+ completely inhibited the degradation of iprodione.3)The metabolites appeared during the degradation of iprodione by strain YJN-G were detected by HPLC.A metabolite kept on accumulating during the degradation and its concentration didn't derease along the extension of the culture time.The metabolite was identified as N-(3,5-dichlorophenyl)-2,4-dioxo-imidazolidin.Accordingly,we speculated that strain YJN-G could convert iprodione to N-(3,5-dichlorophenyl)-2,4-dioxo-imidazolidin and sopropyl carbamic acid by a hydrolase.However,isopropyl carbamic acid was not detected,it may have no UV absorption or have been used as the carbon source for growth by strain YJN-G.Therefore,strain YJN-G actually used isopropyl carbamic acid as the sole carbon source for its growth.As iprodione is able to hydrolyze under basic conditions,we designed experiments to study whether the degradation of iprodione by strain YJN-G was due to the alkaline hydrolysis or not.The results showed that iprodione was converted to 3-formic acid-5-(3,5-dichlorophenyl)glycoluric acid and isopropylamine at pH 9,which was different from the metabolites resulted from the degradation of iprodione by strain YJN-G.When the pH value was adjusted to pH 7,most of the metabolites formed the original state of iprodione.This result confirmed that strain YJN-G degraded iprodione by its hydrolase.4)According to the degradation pathway of iprodione by strain YJN-G,we speculated that the enzyme which converted iprodione to N-(3,5-dichlorophenyl)-2,4-dioxo-imidazolidin and isopropyl carbamic acid was a hydrolase designated as iprodione hydrolase.The optimal temperature and pH for the degradation of iprodione by crude iprodione hydrolase was 30?37 ? and 7.0,respectively.The result of the enzyme distribution experiment showed that iprodione hydrolase was an endoenzme. |
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