Co-metabolic biodegradation of quizalofop-p-ethyl by Methylobacterium populi YC-XJ1 and identification of QPEH1 esterase

Abstract Background Quizalofop-p-ethyl (QPE), a unitary R configuration aromatic oxyphenoxypropionic acid esters (AOPPs) herbicide, was widely used and had led to detrimental environmental effects. For finding the QPE-degrading bacteria and promoting the biodegradation of QPE, a series of studies were carried out. Results A QPE-degrading bacterial strain YC-XJ1 was isolated from desert soil and identified as Methylobacterium populi, which could degrade QPE with methanol by co-metabolism. 97.0% of QPE (50 mg/L) could be degraded within 72 h under optimum biodegradation condition of 35°C and pH 8.0. The maximum degradation rate of QPE was 1.4 mg/L/h, and the strain YC-XJ1 exhibited some certain salinity tolerance. Two novel metabolites, 2-hydroxy-6-chloroquinoxaline (HCQ) and quinoxaline, were found by HPLC-MS analysis. The metabolic pathway of QPE was predicted. The catalytic efficiency of strain YC-XJ1 toward different AOPPs herbicides in descending order was as follows: haloxyfop-p-methyl ≈ diclofop-methyl ≈ fluazifop-p-butyl \u003e clodinafop-propargyl \u003e cyhalofop-butyl \u003e quizalofop-p-ethyl \u003e fenoxaprop-p-ethyl \u003e propaquizafop \u003e quizalofop-p-tefuryl. The genome of strain YC-XJ1 was sequenced using a combination of PacBio RS II and Illumina platforms. According to the annotation result, one α/β hydrolase gene was selected and named qpeh1 which QPE-degrading function has obtained validation. Based on the phylogenetic analysis and multiple sequence alignment with other QPE-degrading esterases reported previously, the QPEH1 was clustered with esterase family V. Conclusion Methylobacterium populi YC-XJ1 could degrade QPE with a novel pathway, and the qpeh1 gene was identified as one of QPE-degrading esterase gene.