Pseudomonas pseudoalcaligenes KF707 possesses a biphenyl-catabolic (bph) gene cluster consisting of bphR1A1A2-(orf3)-bphA3A4BCX0X1X2X3D. The bphR1 (formerly orf0) gene product, which belongs to the GntR family, is a positive regulator for itself and bphX0X1X2X3D. Further analysis in this study revealed that a second regulator belonging to the LysR family (designated bphR2) is involved in the regulation of the bph genes in KF707. The bphR2 gene was not located near the bph gene cluster, and its product (BphR2) exhibited a high level of similarity to NahR (the naphthalene- and salicylate-catabolic regulator belonging to the LysR family) in plasmid NAH7 of Pseudomonas putida. A strain containing a disrupted bphR2 gene failed to grow on biphenyl as a sole source of carbon, and the BphD (2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid hydrolase) activity was significantly reduced compared to that of wild-type strain KF707. Furthermore, the same strain exhibited extremely low transcription of bphR1, bphA1, bphC, bphX0, and bphD. However, when the bphR2 gene was provided in trans to the bphR2-disrupted strain, the transcription level of these genes was restored. These results indicate that bphR2 regulates the bph genes positively as a second regulator together with BphR1.
