Study On The Characteristics And Kinetics Of Biodegradation Of Organophosphate Pesticides By The Aspergillus

Biodegradation of organophosphate pesticides and bioremediation of polluted water and soil are the main focus of current research. In this thesis, we studied the biodegradation characteristics of organophosphate pesticides by the Aspergillus and the related techniques. Separated from the wastewater soil in the pesticide factory of Sannong Group, Fujian Province, We got a Aspergillus G21 which can stand the high-density omethoate(3000mg/L) and degrade the omethoate at a high rate. The strain was identified preparatory as the Aspergillus niger G21. The effects of the Aspergillus G21 on the degradation of omthoate were studied systematically. The Aspergillus G21 can not grow on the substrate, where the only carbon resource was omethoate. Adding other fermentable carbon resource (say, glucose) was the key factor to control the growth of the Aspergillus G21. In the systems using glucose/omethoate as co-substrate, the degradation and intake of glucose and omethoate took place in sequence. At the initial stage, the glucose as the fermentable carbon resource was used preferentially. Only when the glucose was used up, the degradation of omethoate was accelerated。The emphasis of our study was put on the effects of temperature, pH, density of glucose, density of omethoate and added phosphor resource on the growth of cell and its degradation activity of omethoate. Under the optimized conditions (30℃, pH 5.5 and 3g/L glucose, 2000mg/L omethoate ) , after 7-day degradation, the degradation rate of omethoate was 90%. Employing the Fed-Batch culture method, the kinetics of biodegradation of omethoate was studied. It was shown that biodegradation of omethoate was a substrate-inhibited process. At the optimum density of omethoate(900mg/L), the maximum specific degradation rate was 0.5mg/h?gdw. At the larger density of omethoate, the substrate-inhibited effect become dominant and the omethoate degradation rate decreased obviously. By the computer-aided fit, we got the kinetic model and the related parameters for the degradation of omethoate by the Aspergillus G21. Our model well described the relationship between the degradation rate and the density of omethoate, therefore, provided the important guidance to control the Aspergillus G21-aided biodegradation of omethoate。Using GC-MS, the intermediate product of the Aspergillus-aided biodegradation of omethoate was traced and its accumulation was studied. For the first time it was reported that O,O,S-trimethyl phosphorothioate was the main intermediate product of Aspergillu-aided biodegradation of omethoate. The C-C bond between the carbonyl group of omethoate molecule and its adjacent carbon atom was the potential acting site of extracelluar enzyme of the Aspergillus G21. In environment medium, the Aspergillus G21 had strong activity to the further degradation of O,O,S-trimethyl phosphorothioate, and the deleterious intermediate would not accumulate in the medium with increasing the degradation rate of omethoate, but degraded further. Therefore, the Aspergillus G21-aided biodegradation of omethoate was of biological safety. Bioremediation of the contaminated soil is the hotspot in the field of environmental protection. We also studied the bioremediation of the omethoate-contaminated soil by the Aspergillus G21. At the low density pollutant (15mg/kg dry soil), adding the Aspergillus G21 had no obvious intensification on bioremediation, but at the large density pollutant (150~500mg/kg dry soil), adding the Aspergillus G21 obviously increased the degradation rate of omethoate,decreasing the half life time of omethoate pollutant in the soil from 8.9d to 4.9d. Therefore, the Aspergillus G21 is applicable to the bioremediation of polluted soil of high density pollutant. Using the Aspergillus G21 as the female parent, screening and domesticating using glyphosate, the Aspergillus G21b was obtained. the Aspergillus G21b had high activity for the degradation of glyphosate. The biodegradation of glyphosate also showed the obvious substrate-inhibited effect. When the density of glyphosate was 500mg/L, the specific degradation rate reached its maximum 0.016 g/h·gdw. Under the optimized conditions (30℃, pH6.0, glucose density 5~7g/L and glyphosate initial density 300mg/L),after 5d degradation, the degradation rate of glyphosate was up to 97%. The Aspergillus is an environment-friendly microbe. The Aspergillus G21 could stand high-density omethoate and glyphosate, and exhibit high biodegradation activity. The intermediate product of the degradation did not accumulate. Therefore, the Aspergillus G21 has the application potential in the bioremediation of contaminated environment by organophosphates pesticides.