title: Novel 2,4-dichlorophenoxyacetic acid degradation genes from oligotrophic Bradyrhizobium sp. strain HW13 isolated from a pristine environment.
abstract: The tfd genes of Ralstonia eutropha JMP134 are the only well-characterized set of genes responsible for 2,4-dichlorophenoxyacetic acid (2,4-D) degradation among 2,4-D-degrading bacteria. A new family of 2,4-D degradation genes, cadRABKC, was cloned and characterized from Bradyrhizobium sp. strain HW13, a strain that was isolated from a buried Hawaiian soil that has never experienced anthropogenic chemicals. The cadR gene was inferred to encode an AraC/XylS type of transcriptional regulator from its deduced amino acid sequence. The cadABC genes were predicted to encode 2,4-D oxygenase subunits from their deduced amino acid sequences that showed 46, 44, and 37% identities with the TftA and TftB subunits of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) oxygenase of Burkholderia cepacia AC1100 and with a putative ferredoxin, ThcC, of Rhodococcus erythropolis NI86/21, respectively. They are thoroughly different from the 2,4-D dioxygenase gene, tfdA, of R. eutropha JMP134. The cadK gene was presumed to encode a 2,4-D transport protein from its deduced amino acid sequence that showed 60% identity with the 2,4-D transporter, TfdK, of strain JMP134. Sinorhizobium meliloti Rm1021 cells containing cadRABKC transformed several phenoxyacetic acids, including 2,4-D and 2,4,5-T, to corresponding phenol derivatives. Frameshift mutations indicated that each of the cadRABC genes was essential for 2,4-D conversion in strain Rm1021 but that cadK was not. Five 2,4-D degraders, including Bradyrhizobium and Sphingomonas strains, were found to have cadA gene homologs, suggesting that these 2,4-D degraders share 2,4-D degradation genes similar to those of strain HW13 cadABC.
authors.affiliation: Department of Bioengineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan.
authors.forename: Wataru
authors.initials: W
authors.lastname: Kitagawa
authors.forename: Sachiko
authors.initials: S
authors.lastname: Takami
authors.forename: Keisuke
authors.initials: K
authors.lastname: Miyauchi
authors.forename: Eiji
authors.initials: E
authors.lastname: Masai
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Kamagata
authors.forename: James M
authors.initials: JM
authors.lastname: Tiedje
authors.forename: Masao
authors.initials: M
authors.lastname: Fukuda
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000378:metabolism*; D000085:Acetates / Q000378:metabolism*; D001483:Base Sequence; D020369:Bradyrhizobium / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D004926:Escherichia coli; D015870:Gene Expression; D005798:Genes, Bacterial; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D010105:Oxygenases / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013379:Substrate Specificity; D014158:Transcription, Genetic
chemical_list: D000085:Acetates; D004269:DNA, Bacterial; D015084:2,4-Dichlorophenoxyacetic Acid; C445306:2,4-dichlorophenoxyacetic acid oxygenase class III; D010105:Oxygenases