Study Of Biodegradation Of Organophosphorus Pesticide By Stenotrophomonas Acidaminiphila G1

A chlorpyrifos degrading bacteria strain, Stenotrophomonas acidaminiphila G1, has been isolated in this lab before. Strain G1 can’t degrade chlorpyrifos completely but can transform it to trichlorophenol (TCP), a metabolite of chlorpyrifos. And the methyl parathion degradation gene (mpd) has been cloned from G1 in this lab. Data revealed that this strain was highly efficient to degrade methyl parathion (MP). This paper studied the degradation of MP by G1, the location of Methyl Parathion Hydrolase (MPH) which is coded by mpd, and the degradation of other 9 pesticides by this strain.Such as the degradation pathway of chlorpyrifos, G1 was highly efficient to degrade 95% MP of 200mg·L-1 in 24 hours, but can’t degrade p-nitrophenol (PNP), the metabolite of MP. The concentration of PNP was rising along with the decrease of MP in the beginning. After MP was almost degraded the concentration of PNP reached the highest level. And then the concentration of PNP was not changed. Methyl paraoxon and profenofos were used as substrate, respectively, the results were similar to the degradation ofMP.Strain G1 was cultured by enrichment medium at 37 ℃ and shaking at 120 r·min-1 After 24h, the cell culture liquid was transferred into centrifuge tubes and then centrifuged at 5000 rmin-1 forl5min to separate cells from the enrichment solution. The supernatant was discarded. Cells were resuspended in the mineral basal medium after washing by normal saline and the suspension’s optical density (OD) was 1.0 at 600nm. The suspension was regarded as mother liquor. An orthogonal experiment in three factors and three levels was designed by SPSS. The factors were concentration of substrate, incubation temperature and inoculum percentage of bacteria. Degradation was performed in tubes with MP of different concentrations and different inoculum of bacteria, and tubes were incubated in incubators at different temperature with shaken at 120 rpm. All data were analyzed by SPSS, and the analysis of variance and Duncan’s multiple range tests were used. When MP was at 50mg·L-1, the volume of bacteria being 20% and culturing at 40℃, the half-time of degradation of MP was 1.6h. The degradation was in the optimality condition.This paper also studied the localization of MPH. The enzyme activity of MPH was measured by determining the residue of PNP which was produced through the enzymatic degradation of MP. The enzyme activities of MPH from three different components were compared. Strain G1 is a gram negative bacterium, so periplasmic enzyme was extracted by using osmotic shock method, intracellular enzyme was extracted by ultrasonication, and the supernatant of culture media was regarded as extracellular enzyme. The molarity of PNP produced by intracellular enzyme was more higher than the rest two components. So MPH is an intracellular enzyme.Seven kinds of organophosphorus pesticides were chosen to be as the only carbon resource for G1 growth. The results suggested that G1 can’t utilize all of them to growth, but 6 of them can be degraded. The degradation of organophosphorus pesticides was affected by the acting site and the chemical structure of pesiticides.