Biphenyl-inducible promoters in a polychlorinated biphenyl-degrading bacterium, Rhodococcus sp. RHA1.

Five transcriptional promoters of biphenyl-degradation genes in Rhodococcus sp. RHA1 were characterized. We newly identified the etbA4 promoter region, which was located adjacent upstream from a ferredoxin reductase gene, etbA4 and a dihydrodiol dehydrogenase gene, bphB2. The etbA4 promoter activity was determined in RHA1 using a promoter probe vector with a luxAB luciferase reporter gene, and was induced by a variety of aromatic compounds as well as the bphA1, ebdA1, etbA1, and etbD1 promoters. All these promoters were induced by aromatic compounds in a closely related heterologous host, R. erythropolis IAM1399 in the presence of RHA1 bphST genes, suggesting that these five promoters are under the control of bphST-coding two-component regulatory system. Sequence comparison of the bphA1 promoter with the ebdA1 and etbA1 promoters, whose transcription starts were determined by primer extension analysis, revealed a consensus sequence centering 42-bp upstream from the transcription start. This consensus was also conserved in the etbA4 and etbD1 promoters, and deletions of the bphA1 promoter affecting the consensus impaired inducible promoter activity. These results suggest that this consensus plays a role in transcription induction and/or the promotion of biphenyl degradation genes in RHA1.