Enantioselective Degradation Mechanism of Beta-Cypermethrin in Soil From the Perspective of Functional Genes

The behavior and mechanisms of the enantioselective degradation of beta‐cypermethrin were studied in soil. The four isomers were degraded at different rates, and the enantiomer fractions of alpha‐cypermethrin and theta‐cypermethrin exceeded 0.5. Moreover, 3‐phenoxybenzoic acid, phenol, and protocatechuic acid were detected; based on the presence of these metabolites, we predicted the degradation pathway and identified the functional genes that are related to this degradation process. We established quantitative relationships between the data on degradation kinetics and functional genes; we found that the quantitative relationships between different enantiomers differed even under the same conditions, and the genes pobA and pytH played key roles in limiting the degradation rate. Data obtained using path analysis revealed that the same gene had different direct and indirect effects on the degradation of different isomers. A mechanism was successfully proposed to explain the selective degradation of chiral compounds based on the perspective of functional genes. Chirality 27:929–935, 2015. © 2015 Wiley Periodicals, Inc. The degradation pathway of BCYM and the direct and indirect contributions of key rate‐limiting functional genes on the degradation of the four isomers. There are four isomers in BCYM: (+)‐ACYM, (−)‐ACYM, (+)‐ TCYM and (−)‐TCYM. The degradation pathway of these four isomers are the same: soil organisms degraded BCYM by first hydrolyzing the ester linkage in a reaction catalyzed by carboxylesterase (encoded by a key rate‐limiting functional gene pytH) and yielded 3‐PBA; 3‐PBA can further degraded via the cleavage of diphenylether by 3‐phenoxy acid dioxygenase (encoded by another key rate‐limiting functional gene pobA) and yielded phenol and protocatechuic acid. The direct and indirect contributions of these two key ratelimiting functional genes on the degradation of the four isomers revealed that the same functional gene can have different direct and indirect effects on the degradation of different isomers, even under the same conditions. A path analysis of 3‐PBA revealed that pobA was the only key rate‐limiting gene for 3‐PBA degradation.