Biodegradation properties and mechanism of triketone herbicide mesotrione via newly isolated bacterium Klebsiella pasteurii CM-1

Mesotrione is an emerging environmental contaminant with potential hazards to agricultural environment and nontarget organisms. Microbes are major drivers of mesotrione biodegradation. However, understanding of the degradation characteristics, mechanisms and potential applications of the reported bacteria that can be utilized to eliminate mesotrione is very limited. Here, a novel mesotrione-degrading Klebsiella pasteurii CM-1 with excellent environmental adaptability was isolated, which could completely degrade 100 mg/L mesotrione within 20 h under the optimal condition. Metabolic pathway analysis showed that CM-1 degraded mesotrione to 2-(2-hydroxyamino-4-(methylsulfonyl)benzoyl)cyclohexane-1,3-dione, 1,3-dihydro-3-hydroxy-6-(methylsulfonyl)benzo[c]isoxazol-3-yl)cyclohexane-1,3-dione and 2-amino-4-methylsulfonylbenzoic acid. The predicted toxicities of these metabolites were lower than that of mesotrione. Combining genomic analysis and RT-qPCR, nitroreductase-encoding genes nfsA and nfsB were identified as key players driving mesotrione biodegradation. Molecular docking results suggested that residues His215 and Arg218 of NfsA and Lys14, Thr41 and Phe124 of NfsB might be the key sites for their binding to mesotrione. Purified enzyme in vitro assays indicated that NfsA and NfsB could degrade mesotrione under various conditions, and converted it to the same products as CM-1. Some metal cations could significantly enhance the activity of NfsA and NfsB. The Km values of NfsA and NfsB for mesotrione were 0.453 and 1.075 mmol/L. Furthermore, CM-1 could rapidly remove 97.21/96.50% of mesotrione (50 mg/kg) in nonsterilized/sterilized soil within 4 d. This study provided an efficient bioresource with remediation potential for mesotrione residual pollution and new insights into the mechanism of bacterial-mediated mesotrione degradation.