Abstract
Acetamiprid, a chloronicotinyl neonicotinoid insecticide, is among the most commonly used insecticides worldwide, and its environmental fate has caused considerable concern. The compound 1-(6-chloropyridin-3-yl)-N-methylmethanamine (IM 1-4) has been reported to be the main intermediate during acetamiprid catabolism in microorganisms, honeybees, and spinach. However, the molecular mechanism underlying the hydrolysis of acetamiprid to IM 1-4 has not yet been elucidated. In this study, a novel amidase (AceAB) that initially hydrolyzes the C-N bond of acetamiprid to generate IM 1-4 was purified and characterized from the acetamiprid-degrading strain Pigmentiphaga sp. strain D-2. Based on peptide profiling of the purified AceAB and the draft genome sequence of strain D-2, aceA (372 bp) and aceB (2,295 bp), encoding the α and β subunits of AceAB, respectively, were cloned and found to be necessary for acetamiprid hydrolysis in strain D-2. The characteristics of AceAB were also systematically investigated. Though AceA and AceB showed 35% to 56% identity to the α and β subunits of the N,N-dimethylformamidase from Paracoccus aminophilus, AceAB was specific for the hydrolysis of acetamiprid and showed no activities to N,N-dimethylformamide or its structural analogs.IMPORTANCE Acetamiprid, among the top neonicotinoid insecticides used worldwide, is one of the most important commercial insecticides. Due to its extensive use, the environmental fate of acetamiprid, especially its microbial degradation, has caused considerable concern. Although the catabolic pathways of acetamiprid in microorganisms have been extensively studied, the molecular mechanisms underlying acetamiprid biodegradation (except for a nitrile hydratase) remain largely unknown, and the enzyme responsible for the biotransformation of acetamiprid into its main intermediate, IM 1-4, have not yet been elucidated. The amidase AceAB and its encoding genes, aceA and aceB, characterized in this study, were found to be necessary and specific for the initial hydrolysis of the C-N bond of acetamiprid to generate IM 1-4 in Pigmentiphaga sp. strain D-2. The finding of the novel amidase AceAB will greatly enhance our understanding of the microbial catabolism of the widely used insecticide acetamiprid at the molecular level.