Isolation and characterization of a stable 2,4-dichlorophenoxyacetic acid degrading bacterium, Variovorax paradoxus, using chemostat culture

A strain of Variovorax paradoxus degrading 2,4-dichlorophenoxyacetic acid ( 2,4-D) was isolated from the Dijon area (France) using continuous chemostat culture. This strain, designated TV1, grew on up to 5 mM 2,4-D and efficie ntly degraded the herbicide as sole carbon source as well as in presence of soil extracts. It also degraded phenol and 2-methyl, 4-chlorophenoxyacetic acid at 3 mM and 2,4-dichlorophenol at 1 mM. This organism contained a sta ble 200 kb plasmid, designated pTV1, which showed no similarity in its rest riction pattern with the archetypal 2,4-D catabolic plasmid pJP4. However, pTV1 contained an 11 kb BamHI fragment which hybridized at low stringency w ith the 2,4-D degradative genes tfdA, tfdB and tfdR from pJP4. PTV1 partial tfdA sequence showed 77 % similarity with the archetypal tfdA gene sequenc e from Ralstonia eutropha JMP134. Tn5 mutagenesis confirmed the involvement of this gene in the 2,4-D catabolic pathway.