Isolation And Characterization Of Fenoxaprop-P-Ethyl Degrading Bcteria Strain MEPE-0128 And Purification Of A Fenoxaprop-P-Ethyl Hydrolase

Fenoxaprop-p-ethyl (FE) was an aryloxyphenoxypropanoic acid herbicide for controlling of annual grass weeds, and wildly applied in China. Just as other pesticides, aryloxyphenoxypropanoic acid herbicides would pose stresses on organisms and ecosystem when they were applied into the environment.A strain of bacterium, designated as strain MEPE-0128, capable of degrading FE, was isolated from contaminated soils by FE. Strain MEPE-0128 was preliminarily identified as Acinetobacter sp. based on its physiological and biochemical characters and the result of the 16S rRNA gene sequence alignment.The optimal pH for the growth of strain MEPE-0128 was 5.0-10.0. Growth of strain MEPE-0128 was significantly inhibited when the pH was lower than 4.0. The optimal temperature range was wide, lower temperature (20℃) did not show significant inhibition to the growth of strain MEPE-0128, and grew well under aerobic condition. The osmotic pressure for strain MEPE-0128 was 0-10 g-L-1 NaCl. The optimal medium for the growth of strain MEPE-0128 was arabinose as carbon source and organic nitrogen as nitrogen source. The strain MEPE-0128 was sensitive to erythromycin. Strain MEPE-0128 could utilize FE as the sole carbon source for growth, and the total degradation rate was higher than 80% for 50 mg-L"1 FE after 5 days. The optimal temperature of FE degradation by strain MEPE-0128 was 37℃, pH 4.0-10.0 did not show significant influence on the degradation rate of FE, and the autohydrolysis rate improved with decreasing of pH values. With the initial concentration of FE increasing, the degradation rate became lower. The degradation rate of FE was related positively to inoculation level. There was no significant effect to degradation rate by metal ions. During the degradation of FE, major metabolites were analyzed by LC-MS. The proposal metabolic pathways had been deduced as follows:FA and ethanol formed by the cleavage of ester bonds.We studied the degradation of FA, CDHB and HPP which were the potential metabolites of FE by the enriched cultures. The degradation rate were higher than 90% for 50 mg·L-1 FA, CDHB, HPP after 5 days, a strain MEPE-0129could efficiently degradate HPP in 5 days was isolated.Rhodococcus sp. MEPE-0172 was another FE degradative strain isolated by our laborotary. The cell-free extracts showed optimal activity at pH 8.0 on the hydrolysis of FE, The enzyme activity decreased markedly at pH values below 6.0 or above 9.0 and almost completely disappeared at pH4.0, the optimal temperature was 42℃. The enzyme retained more than 80% of its maximum activity at temperatures ranging from 25℃to 42℃. Ag+ seriously inhibited the degradation of FE.The fenoxaprop-p-ethyl esterase from cell-free extract of the strain T was purified up to 369.5-fold by ammonium sulfate precipitation, hydrophobic chromatography, ion-exchange chromatography and superdex-200 with 3% recovery and specific activity was 21.5 U·mg-1. The monomer molecular mass of the esterase was estimated to be 42.3 kDa by SDS-PAGE.