Biodegradation of the Neonicotinoid Insecticide Imidacloprid by Endophytic Bacterium Flavobacterium sp. Strain IM-1 Isolated from Imidacloprid-Treated Host Plants

Imidacloprid is a neonicotinoid applied to protect crops from pests. This study considered endophytic bacteria capable of degrading imidacloprid and aimed to isolate, characterize, and analyze their degradation efficiencies. Approximately 300 endophytic bacterial strains were isolated from imidacloprid-treated plants (Brassica rapa var. perviridis), incubated with imidacloprid, and analyzed by periodic sampling using high-performance liquid chromatography (HPLC). One endophytic strain (IM-1) could degrade 58.40% of the initial concentration of imidacloprid after 28 days of incubation in broth media. The 16S rRNA gene sequence confirmed the degrading strain to be Flavobacterium sp. strain IM-1. A chemical structure associated with 5-hydroxy-imidacloprid with similar fragment patterns was identified as a metabolite by liquid chromatography–tandem mass spectrometry (LC-MS/MS). In soil microcosm studies, imidacloprid degradation by strain IM-1 followed first-order kinetics, with calculated half-lives (T1/2) of 16.75 and 12.74 days under sterile and nonsterile conditions, respectively. Considering the degradation potential of isolated strain IM-1, it could be used to degrade imidacloprid insecticide residues.