Carboxylesterase, a de-esterification enzyme, catalyzes the degradation of chlorimuron-ethyl in Rhodococcus erythropolis D310-1.

Microbial degradation is considered to be the most acceptable method for degradation of chlorimuron-ethyl, a typical long-term residual sulfonylurea herbicide, but the underlying mechanism at the genetic and biochemical levels is unclear. In this work, the genome sequence of the chlorimuron-ethyl-degrading bacterium Rhodococcus erythropolis D310-1 was completed, and the gene clusters responsible for the degradation of chlorimuron-ethyl in D310-1 were predicted. A carboxylesterase gene, carE, suggested to be responsible for carboxylesterase de-esterification, was cloned from D310-1. CarE was expressed in Escherichia coli BL21 and purified to homogeneity. The active site of the chlorimuron-ethyl-degrading enzyme CarE and the biochemical activities of CarE were elucidated. The results demonstrated that CarE is involved in catalyzing the de-esterification of chlorimuron-ethyl. A carE deletion mutant strain, D310-1ΔcarE, was constructed, and the chlorimuron-ethyl degradation rate in the presence of 100 mg L-1 chlorimuron-ethyl within 120 h decreased from 86.5 % (wild-type strain D310-1) to 58.2 % (mutant strain D310-1ΔcarE). Introduction of the plasmid pNit-carE restored the ability of the mutant strain to utilize chlorimuron-ethyl. This study is the first to demonstrate that carboxylesterase can catalyze the de-esterification reaction of chlorimuron-ethyl and provides new insights into the mechanism underlying the degradation of sulfonylurea herbicides and a theoretical basis for the utilization of enzyme resources.