Dual two-component regulatory systems are involved in aromatic compound degradation in a polychlorinated-biphenyl degrader, Rhodococcus jostii RHA1.

A Gram-positive polychlorinated-biphenyl (PCB) degrader, Rhodococcus jostii RHA1, degrades PCBs by cometabolism with biphenyl. A two-component BphS1T1 system encoded by bphS1 and bphT1 (formerly bphS and bphT) is responsible for the transcription induction of the five gene clusters, bphAaAbAcAdC1B1, etbAa1Ab1CbphD1, etbAa2Ab2AcD2, etbAdbphB2, and etbD1, which constitute multiple enzyme systems for biphenyl/PCB degradation. The bphS2 and bphT2 genes, which encode BphS2 and BphT2, virtually identical to BphS1 (92%) and BphT1 (97%), respectively, were characterized. BphS2T2 induced the activation of the bphAa promoter in a host, Rhodococcus erythropolis IAM1399, in the presence of a variety of aromatics, including benzene, toluene, ethylbenzene, xylenes, isopropylbenzene, and chlorinated benzenes, as effectively as BphS1T1. The substrate spectrum of BphS2T2 was the same as that of BphS1T1, except for biphenyl, which is a substrate only for BphS1T1. BphS2T2 activated transcription from the five promoters of biphenyl/PCB degradation enzyme gene clusters as effectively as BphS1T1. The targeted disruptions of the bphS1, bphS2, bphT1, and bphT2 genes indicated that all these genes are involved in the growth of RHA1 on aromatic compounds. The hybrid system with bphS1 and bphT2 and that with bphS2 and bphT1 were constructed, and both systems conducted induced activation of the bphAa promoter, indicating cross-communication. These results indicated that RHA1 employs not only multiple enzyme systems, but also dual regulatory systems for biphenyl/PCB degradation. Comparison of the sequences, including bphS2T2, with the bphS1T1-containing sequences and the corresponding sequences in other rhodococcal degraders suggests that bphS2T2 might have originated from bphS1T1.