|
Pyrethroid,a kind of broad-spectrum insecticide with the structure of multi-benzenes by analogying the natural pyrethrin,is widely used in the field of agricultural production owing to its high efficiency,low toxicity,light-resistance and heat-resistance.But because of its stability,slow degradation rate and low degradation ratio,it caused many problems to the environment and food safety.At present,the most researches on the pyrethroid-degrading enzyme are focused on the effect of single degrading enzyme on one or few pesticides,while the reports on the degrading enzyme or degrading enzyme of mixed bacteria which,at the same time,can degradate kinds of Pyrethroids,are few.Therefore,this research based on the previous relative researches,was done to study the characteristics of degrading enzyme of degrading strains M6R9 and M5R14which,at the same time,can degradate bifenthrin, fenpropathrin and cypermethrin 3.By doing this,we hope we can provide scientific basis for reducing the residence of Pyrethroid in the agricultural product.The results showed that:1. Strain M6R9,identified as Enterobacter aerogenes,is aerobic Gram-positive bacilli,with the length,about(0.8-1.9)μm and the width,about(0.5-1.0)μm,which can make a living by using these three Pyrethroids as carbon source; Strain M5R14,identified as pseudomonas diminuta,is aerobic Gram-negative bacilli,with the size(0.3-0.7)μm,which can make a living by using these three Pyrethroids as its only carbon source.2. The results through the study on the characteristics of M6R9 degrading enzyme indicated:the degrading crude enzyme of this strain is intrace-llular enzyme.The best pH for degrading crude enzyme in degrading bifenthrin, fenpropathrin and cypermethrin3,is 7.5 and the optimum temperature is 30℃.The Michaelis constant and maximum degradation rate depend on the species of Pyrethroid.The degrading crude enzyme could maintain high degrading activity against these three kinds of Pyrethroid if the pH is 6.0-8.0,and the temperature is 20℃-40℃. 3. The results through the study on the characteristics of M6R9 degrading enzyme indicated:the degrading crude enzyme of this strain is intrace-llular enzyme.The best pH for degrading crude enzyme in degrading bifenthrin, fenpropathrin and cypermethrin3,is 6.5 and the optimum temperature is 35℃. The Michaelis constant and maximum degradation rate depend on the species of Pyrethroid. The degrading crude enzyme could maintain high degrading activity against these three kinds of Pyrethroid if the pH is 5.0-8.0,and the temperature is 20℃-50℃.4. The research that was done to study the degrading effect of mixed crude enzyme on bifenthrin, fenpropathrin and cypermethrin3 indicated:the degradation ratio of mixed crude enzyme of different inoculation proportion to thsese three Pyrethroids was different and the overall trend of degradation ratio increases as the increase of the amount of inoculation. The maximum degradation ratio to these three Pyrethroids appeared when the inoculation proportion is 1/1,and the separate ratio was 56.31%、55.76y%、54.91%. The same reaction system, with a single crude enzyme (M6R9 or M5R14) under the same inoculum (crude enzyme solution as a single 2ml, mixed crude enzyme M6R9and M5R14 the 1ml) of bifenthrin, fenpropathrin, cypermethrin degradation Rate (49.54%,46.23% and 47.83% and 44.56%,45.45% and 45.56%) compared to the proportion of mixed inoculation of crude enzyme solution (M6R9/M5R14) 1/1, the degradation ratio of mixed crude enzyme increased separatelyby 7.23%,9.35%,7.07% and10.75%,10.31%,9.35%.In other words,the mixed crude enzyme was more favorable to the degradation of these three kinds of pyrethroid than the single one.
|