Characterization of EstQE, a new member of esterase family VIII from the quizalofop-P-ethyl-degrading bacterium Ochrobactrum sp. QE-9

Abstract

Quizalofop-P-ethyl (QE) is a selective, systemic, post-emergence aryloxyphenoxy propanoate (AOPP) herbicide for the control of annual and perennial grassy weeds in a variety of crops. An efficient QE-degrading bacterial strain, QE-9, was isolated from a QE-manufacturing facility in China and identified as Ochrobactrum sp. A 4.0kb DNA fragment from QE-9 containing a full length esterase encoding gene was cloned and analyzed. Multiple sequence alignment showed that the esterase gene estqe encoded a 382 amino acid protein that contained the conserved S-X-X-K esterase motif and clustered within esterase family VIII, owning to a lack of beta-lactamase activity. Full-length estqe was amplified by PCR and cloned into plasmid pET-29a for functional expression in Escherichia coli BL21 (DE3). The purified recombinant esterase EstQE converted QE to quizalofop acid (QA) at an optimum temperature and pH of 45°C and 8.0, respectively. Enzyme activity was severely inhibited by Cu2+, whereas, Ca2+ and Mg2+ significantly increased enzyme activity to 142 and 122% of the control, respectively. The inhibitors PMSF, pCMB, and DEPC as well as detergent SDS strongly inhibited esterase activity. Furthermore, EstQE was capable of hydrolyzing a wide range of other AOPP herbicides, in the following order of catalytic efficiency, quizalofop-P-ethyl>fenoxaprop-P-ethyl>clodinafop-propargyl>cyhalofop-butyl>quizalofop-P-tefuryl>haloxyfop-P-methyl. These results suggest that EstQE is a potential candidate for remediation of AOPP herbicide-contaminated environments.