Isolation And Identification Of A Simazine-degrading Strain And Its Degradation Characteristics

Simazine?6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine?,a selective and systemic triazine herbicide,is widely used as a sterilant herbicide to control the annual or perennial weeds in the fields of corn,sorghum,sugarcane,tea garden,and orchard as well as most of the monocotyledonous weeds or the non-cultivated extermination weeds.The relatively low soil adsorption capacity and strong water solubility of simazine lead to the potential pollution in the surface water and groundwater.It has stable chemical properties and thus is hard to degrade,leading to long consistent time in soil.Microbial degradation is the main route for dissipation of simazine in soil.In this paper,an effective simazine-degrading strain Y-2,which was isolated from the secondary sedimentation waste water.The growth characteristics of strain Y-2 was studied under enrichment cultivation in the beef extract peptone medium and the degradation conditions of strain Y-2 was optimized by the orthogonal test.The intermediate products and metabolic pathways were also studied to provide material resources and technical support for the pollution remediation of pesticide residues in water and soil.The main results are listed as following:1.A novel bacteria strain isolated from the secondary sedimentation waste water of a pesticide factory was capable of degrading simazine as the unique source of carbon and energy.According to its morphological,physiological and biochemical characteristics and the result of the 16S rDNA sequence homology analysis.this bacteria strain was identified as Pseudomonas stutzeri,namely Pseudomonas stutzeri Y-2.2.The growth of Pseudomonas stutzeri Y-2 was affected by some factors,such as temperature,pH and so on.The results showed that optimum temperature for the growth of the degrading bacteria was 30?,and its optimum pH was in the range of 6-8.Strain Y-2was resistant to erythromycin and roxithromycin below 50 mg·L^-1 but sensitive to ampicillin,chloramphenicol,tetracycline,streptomycin and kanamycin with the concentrations between25¹00 mg·L^-1.3.The best conditions for the degradation of simazine were optimized by the orthogonal test:The sequences of different factors that influenced the degradation of simazine were determined by the orthogonal test of 4 factors?temperature,pH,substrate concentration and inoculation amount?at 3 levels.The results showed that the best conditions for the degradation by strain Y-2 was the temperature of 30?,pH of 7,the inoculation amount of 3%and the substrate concentration of 200 mg·L^-1.pH was the main factor affecting the degradation of simazine.4.The results of degradation of other triazine compounds with the similar structure or functional groups by strain Y-2 showed that the degradation rates of 20 mg·L^-1 atrazine,terbutidine and thalidomide were 100%,30%and 7.3%,respectively.However,it showed no degradation activity for other"Jin"or"through"class of triazine and non-triazine compounds,,except for 20 mg·L^-1 cyanuric acid with the degradation rate after 6h of 56%.5.The intermediate products degraded by strain Pseudomonas stutzeri Y-2 were analyzed by HPLC and UPLC-ESI-MS.By comparing with the standard products,the intermediate products were identified as hydroxylsimazine,ethylamino-ammelide,cyanuric acid and biuret.Meanwhile,it was inferred that the the degradation process included dechlorination,deamination,and decyclization.