Isolation, Identification And Biodegradation Characteristics Of A Bacterial Strain Able To Degrade Bifenthrin

Pyrethroid is a kind of artificial biomimetic compounds to natural pyrethrin, and it’s one of the main agricultural insecticides in recent years. At present, the common used pyrethroid pesticides include cypermethrin, deltamethrin, fenvalerate, and bifenthrin. They are similar in structure, but different in substituent, which makes respective differences in half-life, biotransformation, and toxicity. Studies have shown that these pesticides are generally hard to biodegrade and have the immune system toxicity, cardiovascular toxicity and genetic toxicity to mammals, and some species are carcinogenic, teratogenic and mutagenic.Bifenthrin (BF), developed in the early1980s, is a broad-spectrum and highly efficient synthetic insecticide. However, this compound is stable to light and heat, and cannot easily be washed away form crop surface with rain or surface water. The difficulty of its natural degradation makes it widely remain in the environment, which causes many critical environmental problems.Microbial biodegradation of pesticide residues, especially bacterial biodegradation, is the main way in repair of such sort of environment pollution. Rencently, studies on microbial biodegradation of pyrethroid pesticide have made great progress with the performance of new-found strain, the intensifying degrading mechanism and increasingly degrading effect and stability. But at home and abroad, this research is mainly focus on cypermethrin and deltamethrin, very few on BF, and the BF-degrading bacteria strains that have found grow slow and show low degrading effect. In this study, a BF degrading bacterium was isolated, purified and sorted from the surface soil near the Yangzhou Pesticide Plant, and further researches of identification, degradation characteristics and degradation pathways indicated that the BF-degrading strain S8had great application potential for the future bioremediation of environmental contamination by BF.The main findings are as follows:1. A new efficient BF-degrading bacteria. The strain S8isolated from the long-term pesticide-contaminated soil, the5d-degradation rate reached55.2%during the BF’s concentration of100mg·L-1. Based on the morphological, physiological and biochemical characterization, and phylogenetic analysis of the16S rDNA gene sequence, S8was identified as Acinetobacter sp. and showed the similarity of100%between strain S8and Acinetobacter calcoaceticus.2. The sole carbon source degradation of BF by strain S8. According to the experiment of the sole carbon source culture, S8can degrade BF as the sole carbon source. Strain S8cannot only use acetone and tween-20to grow, therefore, in the culture media system, strain S8grows by BF as the sole carbon source.3. Degradation progress kinetics analysis of strain S8. BF degradation by strain S8reached equilibrium at the3rd day and the progress accords with one order reaction kinetics equation (R2=0.9713, k=0.289d-1, t1/2=60.7h).4. Degradation characters of strain S8. By the experiment of degrading characters, the optimal conditions for BF degradation were at pH6.0-8.0,30℃-35℃and with5%inoculation. S8has good environmental tolerance, especially in pH and temperature.5. Degradation products analysis of strain S8. Degradation firstly can produce Lambda cyhalthrin acid and2-Methyl-3-biphenylmethanol. By analysis of GC-MS, BF firstly was degraded by ester bond fracture and generated smaller carboxylic acid and alcohol:Lambda cyhalthrin acid and2-Methyl-3-biphenylmethanol, and then generate other less toxic or nontoxic compounds with further oxidation, dehydrogenation, and benzene ring opening.6. Improvement of degradation performance of strain S8. Though improvement of re-domestication, UV mutagenesis and carbon starvation, strain S8can enhance degrading performance respectively. After high concentration of re-domestication, the BF5d-degradation rate was improved from57.1%to71.9%. After UV mutagenesis, the strain individuals became obviously larger, and the degrading performance was significantly improved, Z10, Z15, and Z20’s BF5d-degrading rate increased by33.5%,20.2%, and36.3%. After1d carbon starvation, the BF-degrading rate increased by20.8%. But the carbon starvation induced strain with3d and5d respectively increased by4.4%and1.7%.