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 bybphS1 andbphT1 (formerlybphS andbphT ) is responsible for the transcription induction of the five gene clusters,bphAaAbAcAdC1B1 ,etbAa1Ab1CbphD1 ,etbAa2Ab2AcD2 ,etbAdbphB2 , andetbD1 , which constitute multiple enzyme systems for biphenyl/PCB degradation. ThebphS2 andbphT2 genes, which encode BphS2 and BphT2, virtually identical to BphS1 (92%) and BphT1 (97%), respectively, were characterized. BphS2T2 induced the activation of thebphAa 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 thebphS1 ,bphS2 ,bphT1 , andbphT2 genes indicated that all these genes are involved in the growth of RHA1 on aromatic compounds. The hybrid system withbphS1 andbphT2 and that withbphS2 andbphT1 were constructed, and both systems conducted induced activation of thebphAa 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, includingbphS2T2 , with thebphS1T1 -containing sequences and the corresponding sequences in other rhodococcal degraders suggests thatbphS2T2 might have originated frombphS1T1 .