Unveiling the catabolic biodegradation of pymetrozine in Pseudomonas guariconensis strain BYT-5 through genomics studies

Pymetrozine boosts crop yields by managing insect pests, but the United States Environmental Protection Agency (USEPA) has labeled it a potential carcinogen for its detrimental effects on human reproduction and respiratory health. In this study, Pseudomonas guariconensis strain BYT-5, capable of degrading pymetrozine via a typical metabolic pathway as its sole carbon source for growth, was isolated. Genome sequencing and analysis of strain BYT-5 revealed the presence of the pymetrozine hydrolase gene pyzH and two nicotinic acid (NA) catabolic gene clusters, nic1 (nicAB1R1X1C1D1E1F1T1) and nic2 (nicR2X2C2D2E2F2T2B2). Verification of these genes was achieved through heterologous expression, gene knockout, and complementation assays. The gene pyzH initiated the breakdown of pymetrozine into 4-amino-6-methyl-4,5-dihydro-2H-[1,2,4]triazin-3-one (AMDT) and nicotinaldehyde, which was further oxidized to nicotinic acid (NA) by non-specific dehydrogenases. The genes nicAB1, nicC2, and nicX1 sequentially converted NA into 6-hydroxynicotinic acid (6HNA), 2,5-dihydroxypyridine (2,5-DHP), and N-formylmaleamic acid (NFM), respectively. The genes nicD2E2F2 was ultimately responsible for converting NFM to fumaric acid, entering the TCA cycle. Furthermore, the presence of diverse transposases around the pyzH, nic1, and nic2 clusters may facilitate BYT-5's acquisition of genes necessary for pymetrozine degradation. This study elucidates the molecular metabolic mechanism of pymetrozine at the molecular level.