| Dicamba is an effective and popular herbicide all over the world,and also it is potentially toxic to both animals and humans.In this paper,a highly efficient dicamba degrading strain was isolated from the pesticide wastewater treatment pool by enrichment and separation technology,which could utilize dicamba as the sole carbon source for growth and the strain was named as XD-3.It was preliminary identified as Acidovorax delafeldii according to its physiological and biochemical properties and combined with 16S rRNA gene sequence analysis of the strain and its homology comparison.The stain XD-3 growed fast when cultured in LB liquid medium,after 6 h bacteria into the logarithmic growth and continued to 10 h.Then radually into stable growth period after 12 h.The optimum temperature for the growth of strain XD-3 was 30℃,the optimal pH range is 7.0.Liquid volume had effect on the growth of the strain,the less larger in the water the more benefit for the growth.The concentration of NaCl were 0-10 g·L-1,the strains growth better.The strain could highly utilize organic nitrogen source in the test,while had a highest utilization of peptone,however,the use of nitrate nitrogen rate is low.In all the carbon sources,the strain could highly utilize fructose.The followed are Mannitol and glucose.The strain XD-3 could use dicamba as the sole carbon source for growth and was able to degrade 400 mg·L-1 dicamba to undetectable level in 72 h with 5%encapsulated cell mass.The strain degraded dicamba the best at 30℃ and pH 7.0.Metal ions such as Ni2+,Cd2+,Ag+ and Cu2+ inhibited the degradation of dicamba,whereas Mg2+ was in favor to dicamba degradation.The exogenously supplied glucose can promote the degradation of dicamba.The metabolites were detected by LC/MS,three new metabolites had been detected,they were identified as 3,6-Dichlorosalicylic acid,2,5-Dichlorophenol and 1,4-Dichlorobenzene.We propose the following pathway of dicamba degradation by strain XD-3:the first step is the the cleavage of C-O bond in dicamba led to the release of-CH3.Then the 3,6-dichlorosalicylic acid was decarboxylized to 2,5-dichloroanisole.The 2,5-dichloroanisole was correspondingly demethylized to 2,5-dichlorophenol.The third step is dehydroxylation of 2.5-dichlorophenol to 1,4-dichlorobenzene and finally completely mineralized.A novel joint immobilization method was developed by using sodium alginate coupled with biochar to immobilize dicamba-degrading strain XD-3.The results indicate that the mechanical strength and mass transfer performance of sodium alginate-biochar joint immobilization beads were significantly higher than that of sodium alginate immobilized beads.The results from scanning electron microscope also revealed that sodium alginate-biochar joint immobilized beads was more suitable for dicamba-degrading bacteria growth and colonization.The removal efficiencies of joint immobilized bacteria and free bacteria under different environmental conditions were compared.The joint immobilized bacteria showed a better ability in adapting to a wide range of temperature,pH,NaCl and heavy metal ions concentrations.In laboratory-scale fluidized bed bioreactor(FBBR)experiment,the joint immobilized bacteria also showed stable and efficient performance,which would provide the foundation for its engineering application in dicamba wastewater treatment. |
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