2,4-Dichlorophenoxyacetic acid (2,4-D)- and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)-degrading gene cluster in the soybean root-nodulating bacterium Bradyrhizobium elkanii USDA94.
Herbicides 2,4-dichlorophenoxyacetic acid (2,4-D)- and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)-degrading Bradyrhizobium strains possess tfdAα and/or cadABC as degrading genes. It has been reported that root-nodulating bacteria belonging to Bradyrhizobium elkanii also have tfdAα and cadA like genes but lack the ability to degrade these herbicides and that the cadA genes in 2,4-D-degrading and non-degrading Bradyrhizobium are phylogenetically different. In this study, we identified cadRABCK in the genome of a type strain of soybean root-nodulating B. elkanii USDA94 and demonstrated that the strain could degrade the herbicides when cadABCK was forcibly expressed. cadABCK-cloned Escherichia coli also showed the degrading ability. Because co-spiked phenoxyacetic acid (PAA) could induce the degradation of 2,4-D in B. elkanii USDA94, the lack of degrading ability in this strain was supposed to be due to the low inducing potential of the herbicides for the degrading gene cluster. On the other hand, tfdAα from B. elkanii USDA94 showed little potential to degrade the herbicides, but it did for 4-chlorophenoxyacetic acid and PAA. The 2,4-D-degrading ability of the cad cluster and the inducing ability of PAA were confirmed by preparing cadA deletion mutant. This is the first study to demonstrate that the cad cluster in the typical root-nodulating bacterium indeed have the potential to degrade the herbicides, suggesting that degrading genes for anthropogenic compounds could be found in ordinary non-degrading bacteria.
Faculty of Life and Environmental Science, Shimane University 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan.
Shohei
S
Hayashi
Faculty of Life and Environmental Science, Shimane University 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan.
Tomoki
T
Sano
Faculty of Life and Environmental Science, Shimane University 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan.
Kousuke
K
Suyama
Faculty of Life and Environmental Science, Shimane University 1060 Nishikawatsu, Matsue, Shimane 690-8504, Japan. Electronic address: itohkz@life.shimane-u.ac.jp.
Kazuhito
K
Itoh
D015085:2,4,5-Trichlorophenoxyacetic Acid / Q000378:metabolism*; D015084:2,4-Dichlorophenoxyacetic Acid / Q000378:metabolism*; D000085:Acetates / Q000378:metabolism; D001711:Biotransformation; D020369:Bradyrhizobium / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D015870:Gene Expression; D005798:Genes, Bacterial; D006540:Herbicides / Q000378:metabolism*; D005810:Multigene Family; D018517:Plant Roots / Q000382:microbiology*; D013025:Glycine max / Q000382:microbiology*; D015533:Transcriptional Activation / Q000187:drug effects
D000085:Acetates; D006540:Herbicides; D015084:2,4-Dichlorophenoxyacetic Acid; D015085:2,4,5-Trichlorophenoxyacetic Acid; C415326:phenoxyacetic acid
2,4,5-Trichlorophenoxyacetic acid; 2,4-Dichlorophenoxyacetic acid; Bradyrhizobium elkanii USDA94; Herbicide-degrading gene; Non-degrading bacterium; Soybean root-nodulating bacterium