Isolation And Characterization Of A Bensulfuron-Methyl-Degrading Strain And Its Degradation Pathway

Bensulfuron methyl as one of the main representative of the sulfonylurea herbicides, was mainly used for control of weeds in the planting of important food crops of rice, wheat and soybeans and economic crops of peanuts, tea and apples. Long-term repeated application of bensulfuron methyl was likely to cause bensulfuron methyl residues, resulting in the injury to succession sensitive crops and economic losses. Microbial degradation was the main way to eliminate bensulfuron methyl residues in soil.One bensulfuron methyl(BSM)-degrading strain, designated BSM-1, was isolated from the sludge sample of a chemical factory of JiangXi province. It was able to utilize bensulfuron methyl as the sole carbon and energy sources for its growth. It’s degradation rate against20mg·L-1bensulfuron methyl was86.1%within7days. Based on its phenotypic characteristics, physiological and biochemical characteristics analysis,16S rRNA sequencing and homology analysis, strain BSM-1was identified as Achromobacter sp..The optimal carbon source and nitrogen source for strain BSM-1were glucose and yeast extract, respectively. Strain BSM-1grew well in a NaCl concentration of2%to2.5%, too low or too high salt concentration of the NaCl could produce some degree of inhibition to the its growth. Strain BSM-1grew well between25-35℃and the optimal growth temperature was30℃. When the growth temperature was42℃, its growth rate decreased. Strain BSM-1grew well in pH of6-8and optimum pH was7, when the pH value was below4. the growth of the strain was significantly inhibited.The research on the degradation characteristics of strain BSM-1revealed that the inoculum size was correlated positively with the degradation rate within a certain range. When the inoculum size was greater than5%, the increase in the inoculum size did not result in the significant increase of degradation rate. The degradation rate were stable when the250mL flask were filled with medium less than100mL, it was significantly decreased, when the volume of medium was above100mL. Strain BSM-1coule degrade bensulfuron methyl well in pH6-8, its optimum pH was7, high or low pH value:aused the decrease in the degradation rate. The optimum degradation temperature was30℃. Increase or decrease of the temperature would led to the decline in the degradation rate.The degradation pathway of bensulfuron methyl by strain BSM-1was proposed according to the structure analysis of metabolites.The result showed that bensulfuron methyl was degraded to benzyl sulfonic acid by easter bond cleavage, which was converted to ortho-formate benzyl sulfonamide and2-amino-4,6-dimethoxypyrimidine by breakage of the sulfonylurea bridge. Ortho-formate benzyl sulfonamide was further metabolized to ortho-toluic acid through cleavage of carbon-sulfur bond. Ortho-toluic acid cyclohydrated automatically immediately. This is the latest progress in biodegradation pathway of bensulfuron methyl. The results of this study provided strain resources and theoretical basis for the microbial remediation of bensulfuron methyl polluted environments.