Isolation&Characterization Of A Dicamba Degrading Strain SC-1 And Its Degrading Characteristics

Dicamba is widely used in agricultural weeding in China,it is mainly used as a pre-and postemergent herbicide for the control of annual and perennial broadleaf weeds and several grassy weeds.Because of its stable structure and excessive use,it remains a lot in the soil,so more and more people begin to pay attention to the degradation of Dicamba in the soil.Many other countries have reported that the strains which can degrade Dicamba had been found.What s more the pathways of the degradation were also reported,but until now there is only a little research about this in our country.In this essay,Dicamba-degrading strain was isolated;the physical and chemical properties of the stain and the biodegradating characteristic were studied;the initial steps of Dicamba degradation and hydrolase gene were investigated and cloned.Using dicamba as sole carbon source,we isolated a strain which can degrade Dicamba by the enrichment and domestication Technology of wastewater sludge in pesticide factory and it was named SC-1,according to its morphological observation,physiological biochemical test,the comparison sequences of its 16S r DNA and phylogenetic analysis,it was identified as Shingobium sp.The strain can degrade 90%of Dicamba,the optimum temperature and pH for its growth were 30 ?and 7.0 respectively,it can not stand high concentration of NaCl.SC-1 can grow well when using glucose,maltose and as sole carbon,but it can not grow well when using inorganic nitrogen as sole nitrogen sources.SC-1 could use Dicamba as the sole carbon source,it could degrade 90%of 1000mg/L Dicamba within 36 hours.The best conditions for SC-lto degrade Dicamba:Temperature was 30 ?,pH was about 7,the concentration of NaCl was 10 g/L.These conditions were almost the same with the best conditions for SC-1 to grow,and the conditions of enough inoculum and ventilation could promote the degradation of Dicamba.When the concentration of Dicamba was below 1000 mg/L,SC-lcould degrade very well;When the concentration was over 1000 mg/L,SC-1 could not degrade Dicamba even could not grow.Using HPLC and mass spectrometry to analysis the intermediate product of degradation of dicamba by SC-1,the results show that the first step of the degradation by the dicamba bacteria was Methylation reaction,the intermediate product of this reaction was 3,6-DCSA which had no herbicide activity.The key role in the first step of Dicamba degradation was DMO gene,this gene regulated the compound of O-demethylase,it was made up by Reductase,Ferredoxin and Oxygenase.This enzyme system was mainly used in the electron transport chain,NADH(nicotinamide adenine dinucleotide reduced)shuttled a ferredoxin finally to a reductase in the electron transport chain.There are many researches about this enzyme in other countries,also there are many researches about gene DMO,so the gene sequence of DMO has been reported.According to this,we designed the primers.Using the DNA of SC-1 as the template to amplify gene DMO and sequencing the per products,we found that its sequence was the same with what was been reported.So,we could sure that the degradating pathway of Dicamba by SC-1 was the same with what was been reported.