Isolation And Identification Of Two Degradation Strains For Pyrethriod Pesticides And Their Degradation Properties

Synthetic pyrethroid insecticides are broad-spectrum insecticide containing more than one kind of benzene ring structure with the characteristics of high efficiency,low toxicityd and lightersistant,and sprayed frequently on the production of agricultural products.However, due to slow degradation,high residue,and stability in the environment of such pesticides,which has brought environmental and food safety issues.Currently,most researches were focus on one or a few microbial degradation on pyrethroid pesticide-degrading bacteria,rather than the microbial that can degrade a variety of synthetic pyrethroid pesticides or mixed efficient strains of synthetic pyrethroid insebctici-desdegrading bacteria.In view of this,in the paper,two efficient strains of synthetic pyrethroid insecticidesdegrading bacteria,M6R9 and M5R14,isolated from the tame sludge near sewer in pesticide factory of Hangzhou,which can degrade bifenthrin,fenpropathrin and cypermethrin simultaneously,by investigating and identifying the physiological characteristics of the strains,to study the degrading performance of the single strain and mixed strains for synthetic pyrethroid insecticides degradation with a view to reduce and control pyrethrins pesticide residues in agricultural products.The main results were summarized as below:1.Pesticides residues of bifenthrin,fenpropathrin and cypermethrin were determined by gas chromatography equipped with cleaned-capture detector (GC-ECD),the results indicated that,petroleum ether possessed the best extractive effect for three pyrethriods pesticides residues as extractive reagents,the detection limits were 0.001,0.003和0.002 mg·L^-1,for bifenthrin,fenpropathrin and cypermethrin.A mixed standard solution prepared from primary standards of the 3 pesticides,and calibration curve for each of the 3 pesticides was prepared covering the concentration ranges of 0.001 to 20 mg·L^-1,the correlation coefficients of these calibration curves were 0.9994,0.9984 and 0.9943.respectively.The recoveries of 3 standard addition levels of low,medium,high concentrations were 95.37%to 103.41%,with relative standard deviations from 2.36%to 4.11%.This method is quick,simple and suitable for detecting the residues of pyrethroid pesticides, simultaneously.2.Isolation and identification of degradation bacteria M6R9 for pyrethriods pesticides residues and its degradation characteristics were studied,the results indicated that,the strain of M6R9 was identified as Enterobacter aerogenes,which had highly efficient degradation for bifenthrin,fenpropathrin and cypermethrin.By investigating the physiological characteristics of the strain,the results show that the bacterium is a gram-negative aerobe bacilli,size is(0.8-1.9)μm×(0.5-1.0)μm,and is capble of utilizing bifenthrin,fenpropathrin and cypermethrin as sole carbon source. Under the condition of ventilation,(25-30)℃.inoculated amount at OD_415nm=0.2,pH 7.0,pesticide concentration 100 mg·L^-1 and vibrational speed 180 r·min^-1,the degradation efficiencys to bifenthrin,fenpropathrin and cypermethrin are highest by strain M6R9.Under such condition,in the mixture culture medium with 100 mg·L^-1 bifenthrin,fenpropathrin and cypermethrin,the degradation ratios are 55.74%, 55.11%and 55.96%after culturing 3 days,respectively,the degradation processes are fitted for first-order kinetic equation and the half limbs(t_1/2) are 65.4,70.7 and 68.6h respectively.The degradation ability of Enterobacter aerogenes M6R9 on bifenthrin, fenpropathrin and cypermethrin is positively correlated to inoculated amount, vibrational speed and ventilation.3.Isolation and identification of degradation characteristics of the stain M5R14 able to degrade pyrethriods pesticide were studied,the results showed that,the bacterial strain labeled as M5R14 was identified as pseudomonas diminuta.By investigating the physiological characteristics of the strain,the results showed that the bacterium was a bacilli,aerobe,roundness,size was(0.3-0.7)μm,gram-negative,and was capable of utilizing bifenthrin,fenpropathrin and cypermethrin as sole carbon source.Under ventilation,30℃,inoculated amount at OD_415nm=0.2,pH 6.0-7.0, pesticide concentration 100 mg·L^-1,vibrational speed 180 r·min^-1,the degradation efficiency to bifenthrin,fenpropathrin and cypermethrin was highest by the strain M5R14.Under such condition,in the mixture culture medium with 100 mg·L^-1 bifenthrin,fenpropathrin and cypermethrin,the degradation ratios to the above 3 kinds of pyrethriod pesticides were 43.78%,43.91%and 43.75%after incubating 3 days,respectively.The degradation process was fitted for first-order kinetic equation and the half life(t_1/2) were 97.6,106.6 and 101.9h,respectively.The degradation ability of pseudomonas diminuta M5R14 on bifenthrin,fenpropathrin and cypermethrin were positively correlated to inoculated amount at inoculated amount, vibrational speed and ventilation.4.Degrading performance of two efficient mixed strains for synthetic pyrethroid insecticides degradation were studied,it's found that the degradation process was fitted to first-order kinetic equation.Under the optimum inoculated amount at OD_415nm=0.2(the mixed strains M6R9 and M5R14 respectively inoculated OD_415nm= 0.1 at equal proportion,while the single strain M6R9 or M5R14 inoculated OD_415nm= 0.2),the degradation rates of mixed strains for bifenthrin,fenpropathrin and cypermethrin(100 mg·L^-1)increased by 2.5%,3.4%,2.3%and 14.5%,14.6%,15.5%, and the half life(t_1/2) was shorten by 8.1,14.8,13.1h and 40.3,50.7,46.4h,compared with the single strain M6R9 or M5R14 after culturing 3 days in the condition of pH 7.0,30℃,180 r·min^-1.It's proposed that there is a synergistic effect between M6R9 and M5R14 on bifenthrin,fenpropathrin and cypermethrin.