Analysis of Two Gene Clusters Involved in 2,4,6-Trichlorophenol Degradation by Ralstonia pickettii DTP0602

Ralstonia pickettii DTP0602 utilizes 2,4,6-trichlorophenol (2,4,6-TCP) as sole source of carbon and energy. We have characterized hadABC which is involved in the degradation of 2,4,6-TCP. To identify the other genes involved in 2,4,6-TCP degradation, the DNA sequence around hadABC was determined. A regulatory gene, hadR, homologous to the LysR-type transcriptional regulator was located upstream of hadA, but no maleylacetate (MA) reductase gene was located near hadABC. An 8.4-kb DNA fragment containing a MA reductase gene, hadD, was cloned using a DNA probe designed from the N-terminal sequence of purified MA reductase. hadD was located upstream of an open reading frame, hadS, which codes for a homolog of the LysR-type transcriptional regulator. A hadS insertion mutant, DTP62S, constitutively expressed MA reductase when grown on aspartate in the absence of 2,4,6-TCP. MA reductase was repressed in DTP62S supplemented with hadS. HadR and HadS are proposed to be a positive and a negative regulator, respectively. A draft genome sequence analysis revealed that the hadRXABC and hadSYD clusters were separated by 146-kb on the 8.1-Mb chromosome.