HbpR, a New Member of the XylR/DmpR Subclass within the NtrC Family of Bacterial Transcriptional Activators, Regulates Expression of 2-Hydroxybiphenyl Metabolism in Pseudomonas azelaica HBP1

Abstract

The regulation of 2-hydroxybiphenyl and 2,2-dihydroxybiphenyl degradation in Pseudomonas azelaica is mediated by the regulatory gene, hbpR. The hbpR gene encodes a 63-kDa protein belonging to the NtrC family of prokaryotic transcriptional activators and having the highest homology to members of the XylR/DmpR subclass. Disruption of the hbpR gene in P. azelaica and complementation in trans showed that the HbpR protein was the key regulator for 2-hydroxybiphenyl metabolism. Induction experiments with P. azelaica and Escherichia coli containing luxAB-based transcriptional fusions revealed that HbpR activates transcription from a promoter (P hbpC ) in front of the first gene for 2-hydroxybiphenyl degradation, hbpC, and that 2-hydroxybiphenyl itself is the direct effector for HbpR-mediated activation. Of several compounds tested, only the pathway substrates 2-hydroxybiphenyl and 2,2-dihydroxybiphenyl and structural analogs like 2-aminobiphenyl and 2-hydroxybiphenylmethane were effectors for HbpR activation. HbpR is therefore, to our knowledge, the first regulator of the XylR/ DmpR class that recognizes biaromatic but not monoaromatic structures. Analysis of a spontaneously occurring mutant, P. azelaica HBP1 Prp, which can grow with the non-wild-type effector 2-propylphenol, revealed a single mutation in the hbpR gene (T613C) leading to a Trp3Arg substitution at amino acid residue 205. P. azelaica HBP1 derivative strains without a functional hbpR gene constitutively expressed the genes for 2-hydroxybiphenyl degradation when complemented in trans with the hbpR-T613C gene. This suggests the importance of this residue, which is conserved among all members of the XylR/DmpR subclass, for interdomain repression.

Bacterial Transcriptional Regulators for Degradation Pathways of Aromatic Compounds

“…3-Nitrotoluene can also bind XylR without mediating activation (73,221). In several cases, inducing compounds which effect transcription activation are not direct substrates for the target pathway, such as 2-aminobiphenyl and HbpR (97).…”

“…Also, areR is transcribed in the same direction as areCBA but is located upstream of it. Finally, HbpR is the regulatory protein which controls two small operons for 2-hydroxybiphenyl degradation (hbpCA and hbpD) in Pseudomonas azelaica HBP1 (97). The intergenic region between hbpR and hbpC looks as if it has been subject to recent duplication and deletion events, since a small 5Ј part of a second hbpR copy is still present (96).…”

The Biocatalytic Desulfurization Project

“…HbpR is a positive regulator of Pseudomonas azelaica HBP1 that, in the presence of hydroxybiphenyl, activates the transcription of the hbpCA operon, which encodes enzymes for the oxidation of hydroxybiphenyl in its native host (8). By cloning the gene for HbpR and the regulatory sequences upstream of the hbpCA operon into a transcriptional reporter plasmid, the presence or production of HBP could be detected by expression of reporter genes.…”

The RNA Processing Enzyme Polynucleotide Phosphorylase Negatively Controls Biofilm Formation by Repressing Poly-N-Acetylglucosamine (PNAG) Production in Escherichia coli C

“…Therefore, we tested whether this determinant was also involved in pgaABCD control by PNPase. To this aim, we constructed several plasmids (see Table 1) harboring both transcriptional and translational fusions between different elements of the pgaABCD regulatory region and the luxAB operon, which encodes the catalytic subunits of Vibrio harveyi luciferase, as a reporter [37]. Luciferase expression in both pnp + and Δpnp strains was tested using the transcriptional fusion plasmids pΔLpga and pLpga1, which harbor the pgaABCD promoter region (pgaAp) alone (−116 to +32 relative to the transcript start site) and a region encompassing pgaAp and the entire pgaA leader (without its ATG start codon), respectively.…”

“…Luciferase assays were performed as in [37]. Oligonucleotides utilized for Northern blot, real time PCR, and construction of reporter plasmids are listed in Additional file 1: Table S1.…”