Bioinformatics of a Novel Nitrile Hydratase Gene Cluster of the N₂-Fixing Bacterium <i>Microvirga flocculans</i> CGMCC 1.16731 and Characterization of the Enzyme

Abstract

<i>Microvirga flocculans</i> CGMCC 1.16731 can degrade many cyano group-containing neonicotinoid insecticides. Here, its genome was sequenced, and a novel nitrile hydratase gene cluster was discovered in a plasmid. The NHase gene cluster (<i>pnhF</i>) has gene structure β-subunit 1, α-subunit, and β-subunit 2, which is different from previously reported NHase gene structures. Phylogenetic analysis of α-subunits indicated that NHases containing the three subunit (β1αβ2) structure are independent from NHases containing two subunits (αβ). <i>pnhF</i> was successfully expressed in <i>Escherichia coli</i>, and the purified PnhF could convert the nitrile-containing insecticide flonicamid to <i>N</i>-(4-trifluoromethylnicotinoyl)glycinamide. The enzymatic properties of PnhF were investigated using flonicamid as a substrate. Homology models revealed that amino acid residue β1-Glu56 may strongly affect the catalytic activity of PnhF. This study expands our understanding of the structures and functions of NHases and the enzymatic mechanism of the environmental fate of flonicamid.