Characterization of nitrilases from Variovorax boronicumulans that functions in insecticide flonicamid degradation and beta-cyano-L-alanine detoxification

Aims: To characterize the functions of nitrilases of Variovorax boronicumulans CGMCC 4969 and evaluate flonicamid (FLO) degradation and beta-cyano-L-alanine (Ala(CN)) detoxification by this bacterium. Methods and Results: Variovorax boronicumulans CGMCC 4969 nitrilases (NitA and NitB) were purified, and substrate specificity assay indicated that both of them degraded insecticide FLO to N-(4-trifluoromethylnicotinoyl)glycinamide (TFNG-AM) and 4-(trifluoromethyl)nicotinol glycine (TFNG). Ala(CN), a plant detoxification intermediate, was hydrolysed by NitB. Escherichia coli overexpressing NitA and NitB degraded 41.2 and 93.8% of FLO (0.87 mmol.L-1) within 1 h, with half-lives of 1.30 and 0.25 h, respectively. NitB exhibited the highest nitrilase activity towards FLO. FLO was used as a substrate to compare their enzymatic properties. NitB was more tolerant to acidic conditions and organic solvents than NitA. Conversely, NitA was more tolerant to metal ions than NitB. CGMCC 4969 facilitated FLO degradation in soil and surface water and utilized Ala(CN) as a sole nitrogen source for growth. Conclusions: CGMCC 4969 efficiently degraded FLO mediated by NitA and NitB; NitB was involved in Ala(CN) detoxification. Significance and Impact of the Study: This study promotes our understanding of versatile functions of nitrilases from CGMCC 4969 that is promising for environmental remediation.