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Background  The chloroacetamide herbicides pretilachlor is an emerging pollutant. Due to the large amount of use, its presence in the environment threatens human health. However, the molecular mechanism of pretilachlor degradation remains unknown.    Results  Now,  Rhodococcus  sp. B2 was isolated from rice field and shown to degrade pretilachlor. The maximum pretilachlor degradation efficiency (86.1%) was observed at a culture time of 5 d, an initial substrate concentration 50 mg/L, pH 6.98, and 30.1 °C. One novel metabolite  N -hydroxyethyl-2-chloro- N -(2, 6-diethyl-phenyl)-acetamide was identified by gas chromatography-mass spectrometry (GC–MS). Draft genome comparison demonstrated that a 32,147-bp DNA fragment, harboring gene cluster ( EthRABCD   B2  ), was absent from the mutant strain TB2 which could not degrade pretilachlor. The  Eth  gene cluster, encodes an AraC/XylS family transcriptional regulator (EthR B2 ), a ferredoxin reductase (EthA B2 ), a cytochrome P450 monooxygenase (EthB B2 ), a ferredoxin (EthC B2 ) and a 10-kDa protein of unknown function (EthD B2 ). Complementation with  EthABCD   B2   and  EthABD   B2   ,  but not  EthABC   B2   in strain TB2 restored its ability to degrade chloroacetamide herbicides. Subsequently, codon optimization of  EthABCD   B2   was performed, after which the optimized components were separately expressed in  Escherichia coli , and purified using Ni-affinity chromatography. A mixture of EthABCD B2  or EthABD B2  but not EthABC B2  catalyzed the  N- dealkoxymethylation of alachlor, acetochlor, butachlor, and propisochlor and  O -dealkylation of pretilachlor, revealing that EthD B2  acted as a ferredoxin in strain B2. EthABD B2  displayed maximal activity at 30 °C and pH 7.5.    Conclusions  This is the first report of a P450 family oxygenase catalyzing the  O -dealkylation and  N- dealkoxymethylation of pretilachlor and propisochlor, respectively. And the results of the present study provide a microbial resource for the remediation of chloroacetamide herbicides-contaminated sites.

microbial cell factories

A bifunctional enzyme belonging to cytochrome P450 family involved in the O-dealkylation and N-dealkoxymethylation toward chloroacetanilide herbicides in Rhodococcus sp. B2