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Journal of Bacteriology, January 2000, p. 405-417, Vol. 182, No. 2
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

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

Marco C. M. Jaspers,1 Winfried A. Suske,1 Andreas Schmid,2 David A. M. Goslings,1 Hans-Peter E. Kohler,1 and Jan Roelof van der Meer1,*

Swiss Federal Institute for Environmental Science and Technology and Swiss Federal Institute of Technology, CH-8600 Dübendorf,1 and Institute of Biotechnology, Swiss Federal Institute of Technology, CH-8093 Zürich,2 Switzerland

Received 26 April 1999/Accepted 11 October 1999

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 (PhbpC) 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 Trpright-arrowArg 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.

* Corresponding author. Mailing address: EAWAG, Department of Microbiology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland. Phone: 41-1-823 54 38. Fax: 41-1-823 55 47. E-mail: vdmeer{at}eawag.ch.

Journal of Bacteriology, January 2000, p. 405-417, Vol. 182, No. 2
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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