Screening Of Degradation Bacteria Of Acifluorfen And Its Degradation Characteristics And Immobilized Cell

Acifluorfen is a typical diphenyl ether herbicides.It is widely used to control broadleaf weeds in soybean fields and also is potentially toxic to ecological environment.In this paper,a highly efficient acifluorfen degrading strain,named as DK-3,was isolated from the pesticide wastewater treatment pool by enrichment and separation technology.It was preliminary identified as Pseudomonas citronellolis according to its physiological and biochemical properties and combined with 16S rRNA gene sequence analysis.When cultured in LB liquid medium,the results showed that the strain DK-3 entered into the logarithmic phase after 6 h.After that,DK-3 gradually entered into stable growth period after 19 h.The optimum temperature and pH for the growth of strain DK-3 was 30℃and 6.0-8,0,respectively.When the concentration of NaCl was more than 15 g·L-1,the growth of DK-3 was significantly inhibited.The strain could efficiently utilize fructose but sucrose.The strain could highly utilize peptone for the nitrogen source.When the initial concentration of acifluorfen was 100 mg·L-1,the degradation rate of acifluorfen by the strain DK-3 reached 97.2%after 120 h.The best degradation was achieved at 30℃ and pH 7.0-8.0.The degradation of acifluorfen was increased by improving inoculation amount.The degradation was significantly inhibited by addition of 1.0 mmol/LCu2+or Co2+.The degradation rate is 77.3%in the natural soil inoculated with the strain DK-3.On the other hand,67.5%of the acifluorfen was degraded in the sterilized soil.The metabolites were detected by HPLC-MS/MS.Three metabolites were identified by mass spectrometry as 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate,5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-hydroxyl and 3-chloro-4-hydroxyl benzotrifluoride.We propose the following pathway of acifluorfen degradation by strain DK-3:the first step was that acifluorfen was decarboxylated to 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate.The last step was to form 3-chloro-4-hydroxyl benzotrifluoride and p-dihydroxybenzene by cleavage of ether-bond.A novel joint immobilization method was developed by using sodium alginate supported Fe3O4 nanoparticles(Fe3O4/SA)to immobilize acifluorfen-dagrading strain Pseudomonas citronellolis DK-3.The results of experiments showed that when the dosage of Fe3O4 nanoparticles was 90 mg·L-1,the initial concentration of acifluorfen was 100 mg·L-1,degradation rate of acifluorfen was 97.9%.The results from scanning electron microscope indicated that Fe3O4/SA joint immobilized beads was more suitable for acifluorfen-degrading bacteria growth and colonization.The most approrate pH and temperature for degrading acifluorfen by joint immobilized bacteria was 7～8、30℃respectively.Moveover,Fe3O4/SA joint immobilized cells showed a better ability of adapting to a wide range of temperature,pH,NaCl,anti-toxic heavy metal ions and can be used repeatedly.Finally,in laboratory-scale sequencing batch reactor(SBR)experiment,Fe3O4/SA joint immobilized cells could maintain stable operation for 35 days and degradation rate(over 95%).The investigation would provide the foundation for its engineering application in acifluorfen wastewater treatment.