Characterization of the Second LysR-Type Regulator in the Biphenyl-Catabolic Gene Cluster of Pseudomonas pseudoalcaligenes KF707

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Abstract
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.