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Journal of Bacteriology, October 1999, p. 6371-6376, Vol. 181, No. 20
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Campylobacter jejuni Contains Two Fur Homologs: Characterization of Iron-Responsive Regulation of Peroxide Stress Defense Genes by the PerR Repressor

Arnoud H. M. van Vliet,1,dagger Marie-Louise A. Baillon,2,Dagger Charles W. Penn,2 and Julian M. Ketley1,*

Department of Genetics, University of Leicester, Leicester LE1 7RH,1 and School of Biological Sciences, University of Birmingham, Birmingham B15 2TT,2 United Kingdom

Received 16 February 1999/Accepted 13 August 1999

Expression of the peroxide stress genes alkyl hydroperoxide reductase (ahpC) and catalase (katA) of the microaerophile Campylobacter jejuni is repressed by iron. Whereas iron repression in gram-negative bacteria is usually carried out by the Fur protein, previous work showed that this is not the case in C. jejuni, as these genes are still iron repressed in a C. jejuni fur mutant. An open reading frame encoding a Fur homolog (designated PerR for "peroxide stress regulator") was identified in the genome sequence of C. jejuni. The perR gene was disrupted by a kanamycin resistance cassette in C. jejuni wild-type and fur mutant strains. Subsequent characterization of the C. jejuni perR mutants showed derepressed expression of both AhpC and KatA at a much higher level than that obtained by iron limitation, suggesting that expression of these genes is controlled by other regulatory factors in addition to the iron level. Other iron-regulated proteins were not affected by the perR mutation. The fur perR double mutant showed derepressed expression of known iron-repressed genes. Further phenotypic analysis of the perR mutant, fur mutant, and the fur perR double mutant showed that the perR mutation made C. jejuni hyperresistant to peroxide stress caused by hydrogen peroxide and cumene hydroperoxide, a finding consistent with the high levels of KatA and AhpC expression, and showed that these enzymes were functional. Quantitative analysis of KatA expression showed that both the perR mutation and the fur mutation had profound effects on catalase activity, suggesting additional non-iron-dependent regulation of KatA and, by inference, AhpC. The PerR protein is a functional but nonhomologous substitution for the OxyR protein, which regulates peroxide stress genes in other gram-negative bacteria. Regulation of peroxide stress genes by a Fur homolog has recently been described for the gram-positive bacterium Bacillus subtilis. C. jejuni is the first gram-negative bacterium where non-OxyR regulation of peroxide stress genes has been described and characterized.

* Corresponding author. Mailing address: Department of Genetics, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom. Phone: 44-116-2523434. Fax: 44-116-2523378. E-mail: ket{at}le.ac.uk.

dagger Present address: Departments of Medical Microbiology & Gastroenterology, Faculty of Medicine, Vrije Universiteit Amsterdam, 1081 BT Amsterdam, The Netherlands.

Dagger Present address: Waltham Centre for Pet Nutrition, Waltham-on-the-Wolds, Melton Mowbray LE14 4RT, United Kingdom.

Journal of Bacteriology, October 1999, p. 6371-6376, Vol. 181, No. 20
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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