K-086. Transcriptional Repression of Biphenyl Degradation Genes by Biphenyl Metabolites in PCB Degrader, Rhodococcus jostii RHA1

K. Miyauchi1, T. Ito1, K. Sato1, M. Fukuda2;
1Tohoku Gakuin Univ., Miyagi, JAPAN, 2Nagaoka Univ. Tech., Niigata, JAPAN.

Background: Rhodococcus jostii RHA1 is a polychlorinated biphenyls (PCBs) degrader and its PCB degradation genes (bph genes) have been well characterized. In the presence of biphenyl, the transcription of bph genes is upregulated by the two-component system, BphS and BphT. In this study, we found and characterized the transcriptional repression of bph genes in the presence of biphenyl metabolites. Methods: The promoter of bphAa gene (PbphAa) was inserted upstream the luciferase gene in the promoter probe vector, pKLA1. The resulting plasmid pKLAF1 was introduced into RHA1 or its mutant. The transformants were grown on 0.2 x LB broth in the presence of each substrate, and the luciferase activity was measured to estimate the PbphAa activity. Results: When RHA1 harboring pKLAF1 was grown in the presence of biphenyl, the luciferase activity once increased, and then decreased, suggesting that metabolites of biphenyl were responsible for the repression of the transcription from PbphAa. Because it has been shown that the transcription of bph genes is repressed in the presence of benzoate, the transformant was grown in the presence of both biphenyl and benzoate. The luciferase activity was repressed, which suggested that at least benzoate or its metabolites caused the repression. When using the disruption mutant of benA which does not degrade benzoate as a host, the repression was not observed in the presence of benzoate. In the presence of catechol, which is an intermediate compound of benzoate degradation, the repression was observed. Conclusion: In RHA1, the transcriptional repression of the bphAa promoter is caused by catechol or its metabolites.