Genetic characterization of 2,4,6-trichlorophenol degradation in Cupriavidus necator JMP134

The degradation pathway of 2,4,6-trichlorophenol (2,4,6-TCP), a hazardous pollutant, in the aerobic bacterium Cupriavidus necator JMP134(pJP4) (formerly Ralstonia eutropha JMP134) is encoded by the tcp genes. These genes are located in a genetic contest, tcpRXABCYD, which resembles a putative catabolic operon. In this work, these gene sequences were individually disrupted and mutant strains were evaluated for their ability to grow on or degrade 2,4,6-TCP. The tcpX and tcpA mutants completely failed to degrade this compound. Although the tcpC mutant was also unable to grow on 2,4,6-TCP, it still transformed this chlorophenol to 6-chlorohydroquinol. In contrast, the tcpD mutant grew on 2,4,6-TCP, suggesting the presence of additional maleylacetate reductase-encoding genes. Five other open reading frames encoding maleylacetate reductases, in addition to the tcpD gene, were found in the genome of C. necator, and two of them provide this function in the tcpD mutant. The tcpR gene, encoding a putative LysR-type transcriptional regulator, was disrupted, and this mutant strain completely failed to grow on 2,4,6-TCP. Transcriptional fusion studies demonstrated that TcpR activates the expression of the tcp genes, responding specifically to 2,4,6-TCP. The transcriptional start of the tcp operon was mapped, and a putative σ⁷⁰-type promoter was identified.