Screening Of Dominant Bacteria Of Alachlor And Their Degradation Characteristics

Alachlor is a widely used herbicide among amide herbicides.It has the characteristics of broad spectrum,strong selectivity and convenient use.It is a selective pre-emergent herbicide.It is mainly used in corn,peanuts,soybeans,etc.Mainly remove annual grasses and some broadleaf weeds.However,because alachlor has a stable structure,long half-life,and is slightly soluble in water,it will remain in the environment for a long time after long-term use,easily causing phytotoxicity to subsequent crops,and enriching in organisms through food webs,posing a threat to human health.,therefore,has attracted widespread attention.Based on the two screened strains of alachlor dominant bacteria,the effects of temperature,p H and strain dosage on the degradation of alachlor by the dominant bacteria were studied,which enriched the diversity of herbicide degradation resources,and explored the effects of different concentrations of alachlor.Whether alachlor dominant bacteria can be efficiently degraded.At the same time,the content of malondialdehyde(MDA)and the changes of superoxide dismutase(SOD),catalase(CAT),and acetylcholinesterase(Ach E)activities in earthworms were analyzed to characterize alachlor and its metabolites.Toxicity changes,and finally,the dominant bacteria were added to the rhizosphere soil of maize to establish a maize-microbe joint remediation system to explore the effect of the joint remediation system on maize biomass and the remediation effect of alachlor,in order to eliminate amide herbicides.The rational use of chemical species and environmental restoration have laid a theoretical foundation.The results of the study are as follows:1.Two strains of alachlor degrading bacteria were screened from farm soil and the degradation conditions were optimized.By analyzing the morphological characteristics of the strain and 16 Sr DNA sequence analysis,a degrading bacteria was identified as Trichoderma harzianum and named H12.The optimal degradation conditions for 50mg/L alachlor were p H=6.73 and the inoculum amount was 564 mg./L,temperature26.8℃,degradation rate: 96.1%,half-life period of 4.07 d.One was identified as Phyllobacterium myrsinacearum and named as A12.The optimal degradation conditions for 50 mg/L alachlor were p H=5.55,inoculum volume 9.7%,temperature29.2℃,degradation rate: 76.4%,and half-life of 5.88 d.2.The toxicity of alachlor and its metabolites to earthworms was studied.The results showed that when earthworms were exposed to alachlor-contaminated soil,the activities of SOD and CAT in the body were significantly increased,and the activity of Ach E was significantly inhibited,causing oxidative damage and lipid peroxidation in earthworms.After the dominant bacteria degraded alachlor,the toxicity of alachlor was reduced.The order of toxicity of alachlor and its metabolites to earthworms was:alachlor > metabolites of strain H12 > metabolites of strain A12.3.The combined effect of degrading bacteria and corn in remediation of alachlorcontaminated soil was studied.The results showed that the combined remediation of maize and strain A12 was similar to that of A12 and maize alone in remediation of alachlor,but both were higher than the natural degradation rate of soil.When the alachlor concentration was 2 mg/kg and 5 mg/kg,the biomass of maize increased significantly,indicating that the combined restoration of alachlor can increase the biomass of plants within a certain concentration range.The combined restoration of maize and strain H12 improved the degradation rate of alachlor,and the biomass of maize increased significantly when the alachlor concentration was 2 mg/kg and 5 mg/kg,but H12 had a higher concentration of alachlor.The amine degradation effect is not good.Alachlor in soil was not affected by indigenous microorganisms during the degradation process,and the combined remediation application of degrading bacteria and corn could effectively remediate alachlor-contaminated soil.