Extracellular enzyme mediated biotransformation of imidacloprid by white-rot fungus Phanerochaete chrysosporium: Mechanisms, pathways, and toxicity

As one of the widely used neonicotinoid insecticide, imidacloprid (IMI) poses serious threat on many kinds of non-target species. The acceleration of its removal from the contaminated environment is therefore an urgent task. Herein, the transformation of IMI by white-rot fungus Phanerochaete chrysosporium was examined, and the reaction mechanism underlying enzymes-mediated IMI biotransformation was elucidated. In addition, transformed products, pathways, and toxicity to Escherichia coli and Microcystis aeruginosa or the growth of rice seeds were investigated. P. chrysosporium could efficiently transform 93.5% of IMI for 6 days primarily through biotransformation, in which extracellular manganese peroxidase and lignin peroxidase substantially responded to transform IMI. IMI mainly underwent nitrate reduction, hydroxylation, and de-chlorination. A less neurologically toxic major metabolite of IMI, 6-chloronicotinic acid, was detected. Molecular dynamics simulation demonstrated that IMI stably bonded to active pocket of extracellular enzymes. This study reveals the key metabolic mechanism and fate of IMI in environment, and highlights the potential of fungi for IMI transformation.