Chlorimuron ethyl

Chlorimuron-ethyl is a typical long-term residual sulfonylurea herbicide, and strategies for its removal have attracted increasing attention. Microbial degradation is considered the most acceptable dissipation method. In this study, we optimized the cultivation conditions (substrate concentration, pH, inoculum concentration, and temperature) of the chlorimuron-ethyl-degrading bacterium Rhodococcus sp. D310-1 using response surface methodology (RSM) to improve the biodegradation efficiency. A maximum biodegradation rate of 88.95 % was obtained. The Andrews model was used to describe the changes in the specific degradation rate as the substrate concentration increased. Chlorimuron-ethyl could be transformed with a maximum specific degradation rate (q max), half-saturation constant (K S), and inhibition constant (K i) of 0.4327 day(-1), 63.50045 mg L(-1), and 156.76666 mg L(-1), respectively. Eight biodegradation products (2-amino-4-chloro-6-methoxypyrimidine, ethyl 2-sulfamoyl benzoate, 2-sulfamoyl benzoic acid, o-benzoic sulfimide, 2-[[(4-chloro-6-methoxy-2-pyrimidinyl) carbamoyl] sulfamoyl] benzoic acid, ethyl 2-carbonyl sulfamoyl benzoate, ethyl 2-benzenesulfonyl isocyanate benzoate, and N,N-2(ethyl formate)benzene sulfonylurea) were identified, and three possible degradation pathways were proposed based on the results of high performance liquid chromatography HPLC, liquid chromatography tandem mass spectroscopy (LC-MS/MS), and Fourier transform infrared spectroscopy (FTIR) analyses and the relevant literature. This systematic study is the first to examine the chlorimuron-ethyl degradation pathways of the genus Rhodococcus.

Microbial degradation is one of the most efficient and reliable ways to remove the residues of Chlorimuron-ethyl in the environments such as soil and water. In this study, a glutathione-s-transferase (GST) gene Kj-gst was cloned from the Chlorimuron-ethyl degrading bacterial strain Klebsiella jilinsis 2N3. Results showed that Kj-gst played a key role in the degradation of Chlorimuron-ethyl by strain 2N3. The mutant with gene Kj-gst knocked out showed reduced relative activity up to 70% compared with the wild type in 8 h in culture. After the knockout gene was complemented, the degradation ability of the complement mutant was essentially comparable to that of the wild type. The protein Kj-GST (50 μg) obtained from the gene Kj-gst expressed and purified in E. coli strain BL21(DE3) was capable of degrading Chlorimuron-ethyl with an initial concentration of 50 mg/mL by 42.91% under the optimal conditions (15 °C and pH = 7). Point mutation experiments on a glycine located at position 101 (Glu101) confirmed that the H site of glutathione (GSH) is the key component in Kj-GST for degrading Chlorimuron-ethyl. We conclude that Kj-GST is demonstrated for the first time to degrade Chlorimuron-ethyl with its main functional site identified at the H site of GSH, shedding insight to revealing the molecular mechanisms of degrading Chlorimuron-ethyl by Klebsiella jilinsis 2N3.

Excessive application of chlorimuron-ethyl has led to soil contamination and limited crop rotation; therefore, tactics to decrease and eliminate residual chlorimuron-ethyl in the environment have attracted increasing attention. In this study, two chlorimuron-ethyl-degrading bacterial strains (Rhodococcus sp. D310-1; Enterobacter sp. D310-5) were used to ferment and prepare a chlorimuron-ethyl-degrading bacterial consortium. To improve the degradation efficiency of the bacterial consortium, the cultivation conditions were optimized using response surface methodology (RSM). The maximum biodegradation rate (87.42%) was obtained under optimal conditions (carbon concentration, 9.21gL-1; temperature, 26.15°C; pH, 6.95). The rate of chlorimuron-ethyl degradation by the bacterial consortium in the chlorimuron-ethyl-contaminated soil was monitored and reached 80.02% at the end of a 60-d incubation period. Illumina MiSeq sequencing results showed that microbial diversity was high, and 33 phyla were identified in the analyzed samples. Proteobacteria, Acidobacteria, Acidobacteria, Firmicutes and Bacteroidetes were present in relatively high abundances in the samples. The bacterial consortium made a positive impact on the remediation of chlorimuron-ethyl-contaminated soil and somewhat altered the composition of the bacterial community in the chlorimuron-ethyl-contaminated soil. These findings provide highly valuable information on the production of bacterial consortium for the remediation of chlorimuron-ethyl and other sulfonylurea-herbicide-contaminated soil.