THE TFDK GENE-PRODUCT FACILITATES UPTAKE OF 2,4-DICHLOROPHENOXYACETATE BY RALSTONIA-EUTROPHA JMP134(PJP4)

Uptake of 2,4-dichlorophenoxyacetate (2,4-D) by Ralstonia eutropha JMP 134(pJP4) was studied and shown to be an energy-dependent process. The uptake system was inducible with 2,4-D and followed saturation kineti cs in a concentration range of up to 60 mu M, implying the involvement of a protein in the transport process. We identified an open reading frame on plasmid pJP4, which was designated tfdK, whose translation pr oduct TfdK was highly hydrophobic and showed resemblance to transport proteins of the major facilitator superfamily. An interruption of the tfdK gene on plasmid pJP4 decimated 2,4-D uptake rates, which implies a role for TfdK in uptake. A tfdA mutant, which was blocked in the fir st step of 2,4-D metabolism, still took up 2,4-D. A mathematical model describing TfdK as an active transporter at low micromolar concentrat ions fitted the observed uptake data best.