Mesotrione is a selective herbicide belonging to the triketone family commonly used on maize cultures since 2003. A mesotrione-transforming Bacillus megaterium Mes11 strain isolated from an agricultural soil was used as a model to identify the key enzymes initiating the biotransformation of this herbicide. Two enzymes (called NfrA1 and NfrA2/YcnD) were identified and functionally and structurally characterized. Both belong to the NfsA FRP family of the Nitro FMN reductase superfamily (Type I oxygen-insensitive nitroreductase) and show optimal pH and temperature of 6-6.5 and 23-25°C, respectively. Both undergo a ping-pong Bi-Bi mechanism, with NADPH and NADPH/NADH as cofactors for NfrA1 and NfrA2/YcnD respectively. Interestingly, both are also able to reduce various nitro-compounds including pesticides, antibiotics, one prodrug and 4-methylsulfonyl-2-nitrobenzoic acid, one of the mesotrione metabolites retrieved in the environment. This study constitutes the first identification of mesotrione-transforming enzymes. These enzymes (or their corresponding genes) could be used as biomarkers to predict the capacity of ecosystems to transform mesotrione and to assess their contamination both by the parent molecule and/or by the metabolites.
- Copyright 2016 The Author(s)
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