Isolation, identification and application of a fenoxaprop ethyl-degrading strain Rhodococcus sp. DSB-1

[Objective] The purpose of this study is to isolate and identify the high-efficient degradation strains of fenoxaprop ethyl, providing strain resources and theoretical basis for the development of degradation agents, enhancing the in-situ bioremediation of fenoxaprop ethyl residue contaminated soil, and ensuring the safety of cucumber products. [Methods] The degradation strain was isolated by enrichment culture method and identified by morphology, physiological, biochemical characteristics and 16S rRNA gene evolution analysis. Intermediate products during fenoxaprop ethyl degradation were analyzed by HPLC/MS. The key hydrolase gene was cloned by shotgun method, and heterologously expressed. Michaelis-Menten double reciprocal curve and orthogonal tests were used to determine the enzyme kinetic and liquid fermentation parameters of the degradation strain. Through the irrigation of degradation strain, the fenoxaprop ethyl degradation in cucumber rhizosphere soil and the enhancement effect of mannitol on degradation efficiency were studied. [Results] Rhodococcus sp. DSB-1 was able to transform 100 mg/L fenoxaprop ethyl to fenoxaprop acid as sole carbon source within 24 h. The optimum degradation temperature and pH were 30 °C and 8.0, respectively. A fenoxaprop ethyl hydrolase gene named pepE was cloned from the genome of strain DSB-1 by shotgun method. The K_m and k_cat/K_m of the hydrolase PepE towards fenoxaprop ethyl were 28.2 μmol/L and 11.0 L/(μmol·s). The degradation agent acquired possessed the highest degradation efficiency towards fenoxaprop ethyl under the fermentation conditions: temperature of 30 °C, ventilation rate of 1:0.4, stirring speed of 200 r/min and culture time of 48 h. Strain DSB-1 could colonize on the cucumber root surface, and completely degraded 10 mg/kg fenoxaprop ethyl residue in cucumber rhizosphere soil within 12 d. Addition of mannitol could improve the degradation efficiency by 14.8% compared with the non-added treatment. [Conclusion] Strain DSB-1 could be potentially applied in bioremediation of fenoxaprop ethyl contaminated soil.