Novel 2,4-dichlorophenoxyacetic acid degradation genes from oligotrophic Bradyrhizobium sp. strain HW13 isolated from a pristine environment.
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.
Kitagawa
Wataru
W
Department of Bioengineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan.
Takami
Sachiko
S
Miyauchi
Keisuke
K
Masai
Eiji
E
Kamagata
Yoichi
Y
Tiedje
James M
JM
Fukuda
Masao
M
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
D000085:Acetates; D004269:DNA, Bacterial; D015084:2,4-Dichlorophenoxyacetic Acid; C445306:2,4-dichlorophenoxyacetic acid oxygenase class III; D010105:Oxygenases