Glucose-mediated transcriptional repression of PCB/biphenyl catabolic genes in Rhodococcus jostii RHA1.

Rhodococcus jostii RHA1, a Gram-positive polychlorinated biphenyl (PCB) degrader, exhibited biphasic growth in a medium containing biphenyl (BPH) and glucose (Glc), with consumption of Glc and low 2,3-dihydroxybiphenyl 1,2-dioxygenase activity in the first growth stage. These results suggested the repression of BPH metabolism in the presence of Glc, in which RHA1 preferentially utilized Glc in the first growth stage and BPH in the second stage. A reporter assay using a transcriptional fusion of the bphAa promoter (P(bphAa)) and the luxAB luciferase genes was performed, and lower luciferase activity was observed during the first growth stage, indicating transcriptional repression of P(bphAa) activity in the presence of Glc. Transcription levels of the representative genes of five BPH catabolic enzyme gene clusters (bph/etb gene clusters) and their transcriptional regulatory genes (bphST) were examined by real-time reverse transcription PCR. The results obtained indicate that transcription of the targeted bph/etb genes, which were upregulated by BPH, was repressed in the presence of Glc. Among the substrates examined, fructose in addition to Glc induced the repression of P(bphAa) transcription. These results indicate that BPH utilization in RHA1 is under the control of carbon catabolite repression at the transcriptional level in addition to BphST-dependent transcriptional regulation.