Degradation Characteristics Of Triadimefon Degrading Bacteria SM3 And Its Application In Polluted Soil

Triadimefon is widely used in wheat,corn,fruits,vegetables,flowers and other crops to control rust and powdery mildew as well as to regulate plant growth because of its high broad-spectrum activity,fast fungicidal speed,long duration of action and strong absorption and conduction.With the massive use of triadimefon in agricultural production,excessive amounts of triadimefon will enter the soil environment in a direct or indirect manner.Meanwhile,due to its high stability,mobility and adsorption,it accumulates in the soil environment for a long time,posing a threat to the ecosystem,affecting the ecosystem balance and eventually human health and economic well-being,so the problem of triadimefon residue contamination in the environment needs to be addressed urgently.Microbial remediation has become a research hotspot for environmental pollution management in recent years because of its advantages of low cost,high efficiency,no secondary pollution and easy operation.Microbial degradation of pesticides has been widely studied at home and abroad,and strains of pesticide degradation have been isolated and screened,and with the increasing depth of research,microbial species of pesticide degradation have been discovered,and the degradation effect has been steadily improved,and some microorganisms have been applied in soil pollution remediation.However,the types of microbial degradation of pesticides are mostly concentrated in herbicides and insecticides,and the microbial degradation of fungicides is less studied,and there are few studies have been reported on triadimefon degrading bacteria.In this study,an efficient triadimefon degrading bacteria strain SM3,which was screenedby the group in the early stage,was used to study the effects of various environmental factors on the degradation characteristics of triadimefon under simulated laboratory conditions,and on this basis,the localization and enzymatic properties of the strain SM3 degrading enzymes were studied,and then the strain SM3 was applied to remediate triadimefon contaminated soil,analyze the degradation dynamics of triadimefon in soil,determine its degradation effect on triadimefon This study provides a theoretical basis for the further use of microbial degradation of triadimefon contaminated environment.The main research results are as follows.1.Study on the growth and degradation characteristics of triadimefon degrading bacteria The effects of different temperature,p H,inoculum,salinity and glucose content on the growth of strain SM3 and on the degradation of triadimefon were investigated by single-factor experiments.Initially,the optimal conditions for the growth of strain SM3 and for the degradation of triadimefon were obtained as follows:temperature 30°C,p H 7.0,inoculum level 5%,salt concentration 10 g/L and glucose content 1%.2.Response surface analysis to optimize the degradation conditions of degradation bacteria.The degradation conditions of strain SM3 were optimized by using BBD experimental design and response surface analysis.The results showed that the theoretical optimal value of degradation rate of triadimefon by strain SM3 could reach 87.61%at p H 7.3,7%inoculum and 31.2℃.The actual degradation of triadimenone by strain SM3 under these conditions was 86.05%（the average of three replicates）and the fit with the theoretical optimum value was 98.22%,indicating that the optimization of the conditions for the degradation of triadimenone by strain SM3 through the response surface method is reasonable and effective,and has practical significance.3.Study on the enzymatic properties of triadimefon degrading bacteria.The crude enzyme solution of intracellular enzyme,extracellular enzyme and periplasmic enzyme of strain SM3 was extracted,and the localization analysis of the degrading enzymes was performed.The results showed that the intracellular enzyme degraded triazolone better than the extracellular and periplasmic enzymes,and the degradation rate could reach 62.64%at 36 h.It can be inferred that the key enzyme for the degradation of triadimefon by strain SM3 is the intracellular enzyme.The conditions for the enzymatic degradation of triadimefon by this enzyme:the optimum p H was 7,the optimum temperature was 30℃.The enzyme had good degradation activity in the temperature range of 10-30℃and p H range of 6.0-8.0,indicating that the enzyme has good tolerance to heat and p H.Different metal ions produced different effects on the enzyme activity,Fe²⁺,Cu²⁺,Zn²⁺had an inhibitory effect on the enzyme activity,Ca²⁺,Mg²⁺,Mn²⁺had a promotional effect on the enzyme activity.The Mie constant（Km）of the enzyme was 67.477 mmo L/m L,and the maximum reaction rate（Vmax）was 1.3537 mmo L/h.4.Study on the application of triadimefon degrading bacteria in soil.Laboratory simulated triadimefon contaminated soil was remediated using strain SM3 to analyze the degradation dynamics of triadimefon in soil and to determine the degradation effect of strain SM3 on triadimefon.When the concentration of triadimefon in soil was 0.4mg/kg,2.0 mg/kg and 5.0 mg/kg,the degradation half-lives of the treated groups with strain SM3 were 4.72 d,13.08 d and 21.67 d,respectively,while the degradation half-lives of the treated groups without strain SM3 were 16.12 d,33.01 d and 46.21 d,respectively.The degradation half-lives of triadimefon were shortened by 70.72%,60.38%and 53.11%,respectively,compared with those of the treatment group without strain SM3.When the concentration of triadimefon was 0.4 mg/kg,the degradation rate of triadimefon was the fastest,reaching 99.7%at 25 d.When the concentration was 5 mg/kg,the maximum degradation rate of triadimefon was only 58.1%.The results indicated that the less the amount of triadimefon was added,the more easily it was degraded in the soil and the shorter the residual period.