A novel pathway for initial biotransformation of dinitroaniline herbicide butralin from a newly isolated bacterium Sphingopyxis sp. strain HMH

•Herbicide butralin degrading bacteria was isolated from the agricultural field.•A gene encoding a novel multi-functional flavin-nitroreductase NfnB was identified.•NfnB was expressed in E. coli and purified to homogeneity.•NfnB biotransformed butralin to 5-tert-butyl-3-nitrobenzene-1,2- diamine.•A novel pathway for butralin biotransformation by the isolated strain was proposed.