title: Molecular characterization of the enzymes involved in the degradation of a brominated aromatic herbicide.
abstract: Dehalogenation is the key step in the degradation of halogenated aromatics, while reductive dehalogenation is originally thought to rarely occur in aerobes. In this study, an aerobic strain of Comamonas sp. 7D-2 was shown to degrade the brominated aromatic herbicide bromoxynil completely and release two equivalents of bromides under aerobic conditions. The enzymes involved in the degradation of bromoxynil to 4-carboxy-2-hydroxymuconate-6-semialdehyde, including nitrilase, reductive dehalogenase (BhbA), 4-hydroxybenzoate 3-monooxygenase and protocatechuate 4,5-dioxygenase, were molecularly characterized. The novel dehalogenase BhbA was shown to be a complex of a respiration-linked reductive dehalogenase (RdhA) domain and a NAD(P)H-dependent oxidoreductase domain and to have key features of anaerobic respiratory RdhAs, including two predicted binding motifs for [4Fe-4S] clusters and a close association with a hydrophobic membrane protein (BhbB). BhbB was confirmed to anchor BhbA to the membrane. BhbA was partially purified and found to use NAD(P)H as electron donors. Full-length bhbA homologues were found almost exclusively in marine aerobic proteobacteria, suggesting that reductive dehalogenation occurs extensively in aerobes and that bhbA is horizontally transferred from marine microorganisms. The discovery of a functional reductive dehalogenase and ring-cleavage oxygenases in an aerobe opens up possibilities for basic research as well as the potential application for bioremediation.
authors.affiliation: Department of Microbiology, Key Lab of Microbiological Engineering of Agricultural Environment, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, 210095, Nanjing, China.
authors.forename: Kai
authors.initials: K
authors.lastname: Chen
authors.forename: Linglong
authors.initials: L
authors.lastname: Huang
authors.forename: Changfeng
authors.initials: C
authors.lastname: Xu
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Liu
authors.forename: Jian
authors.initials: J
authors.lastname: He
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Zinder
authors.forename: Shunpeng
authors.initials: S
authors.lastname: Li
authors.forename: Jiandong
authors.initials: J
authors.lastname: Jiang
mesh_terms: D000332:Aerobiosis; D001711:Biotransformation; D001965:Bromides / Q000378:metabolism; D020585:Comamonas / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004798:Enzymes / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D022761:Gene Transfer, Horizontal; D006540:Herbicides / Q000378:metabolism*; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D008969:Molecular Sequence Data; D009570:Nitriles / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D001965:Bromides; D004269:DNA, Bacterial; D004798:Enzymes; D006540:Herbicides; D009570:Nitriles; C006826:bromoxynil