Screening Of Highly Efficient Degradation Bacteria Of Bromoxynil Octanoate And Its Degradation Characteristics And Immobilized Cell

Bromoxynil octanoate, the most widespread herbicide applied to maize, is potentially toxic to both animals and humans. In this paper, a highly efficient bromoxynil octanoate degrading strain was isolated from the pesticide wastewater treatment pool by enrichment and separation technology, which could utilize bromoxynil octanoate as the sole carbon source for growth and the strain was named as XB2. It was preliminary identified as Acinetobacter sp. according to its physiological and biochemical properties and combined with16S rRNA gene sequence analysis of the strain and its homology comparison.The stain XB2growed fast when cultured in LB liquid medium, after2.5h bacteria into the logarithmic growth and continued to8h. Then radually into stable growth period after10h. The optimum temperature for the growth of strain XB2was30℃, the optimal pH range is6.0-8.0. Ventilation had effect on the growth of the strain, larger dissolved oxygen in the water was more benefit for the growth. The concentration of NaCl had great impact on the growth of stain XB2, when the concentration of NaCl were0-10g-L-1, the strains growth better, more than15g-L", strains are significantly inhibited growth. The strain could highly utilize organic nitrogen source in the test, while had a highest utilization of peptone. In all the carbon sources, the strain could highly utilize fructose. The followed are Mannitol, xylose and glucose. The Strain XB2are resistant to ampicillin and chloramphenicol, and more sensitive to carbenicillin, kanamycin, gentamicin and streptomycin.The strain XB2could use bromoxynil octanoate as the sole carbon source for growth and was able to degrade100mg·L-1bromoxynil octanoate to undetectable level in72h. The degradation of bromoxynil octanoate could reach99.43%. The strain degraded bromoxynil octanoate the best at30℃and pH7.0-8.0. The lower initial concentration, the easier utilization of bromoxynil octanoate by the strain. Improving inoculation rate speeded up the degradation of bromoxynil octanoate. Degradation in soil inoculated with bacteria XB2could accelerate the degradation of bromoxynil octanoate. The relative degradation rate is81.14%in the natural soil inoculated with the strain XB2. The indigenous microbiology and the exogenous degradation bacteria both degraded bromoxynil octanoate, and improved the soil degradation rate of bromoxynil octanoate.The metabolites were detected by MS/MS, three new metabolites had been detected, they were identified as3-bromo-4-hydroxybenzoic acid, bromoxynil and3,5-dibromo-4-hydroxybenzoic acid. We propose the following pathway of bromoxynil octanoate degradation by strain XB2:the first step is the scission of the ester bond to form bromoxynil, bromoxynil then transformed to3,5-dibromo-4-hydroxybenzoic acid due to the hydrolysis of nitriles, and debromination finally results in the formation of3-bromo-4-hydroxybenzoic acid. The performance of bromoxynil octanoate degradation by crude enzyme and induced enzyme showed that the strain XB2were induced to produce the enzyme debromination by bromoxynil octanoate.Used sodium alginate embedding the bromoxynil octanoate degrading strain XB2, results showed that mechanical strength of immobilized beads best and the degradation of bromoxynil octanoate effect was best when the concentration of sodium alginate was2%, the concentration of CaCl2was3%and the packet bacteria were1.5g·L-1, immobilized time was4h. The degradation rate of immobilized bacteria was slower than the free bacteria, but immobilized bacteria could tolerance pH and temperature in a wider range.