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Journal of Bacteriology, September 2000, p. 5059-5069, Vol. 182, No. 18
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The Redox-Sensitive Transcriptional Activator OxyR
Regulates the Peroxide Response Regulon in the Obligate Anaerobe
Bacteroides fragilis
Edson R.
Rocha,
Gary
Owens Jr., and
C. Jeffrey
Smith*
Department of Microbiology and Immunology,
East Carolina University School of Medicine, Greenville, North
Carolina 27858-4354
Received 8 March 2000/Accepted 7 June 2000
The peroxide response-inducible genes ahpCF,
dps, and katB in the obligate anaerobe
Bacteroides fragilis are controlled by the redox-sensitive
transcriptional activator OxyR. This is the first functional oxidative
stress regulator identified and characterized in anaerobic bacteria.
oxyR and dps were found to be divergently transcribed, with an overlap in their respective promoter regulatory regions. B. fragilis OxyR and Dps proteins showed high
identity to homologues from a closely related anaerobe,
Porphyromonas gingivalis. Northern blot analysis revealed
that oxyR was expressed as a monocistronic 1-kb mRNA and
that dps mRNA was approximately 500 bases in length. dps mRNA was induced over 500-fold by oxidative stress in
the parent strain and was constitutively induced in the
peroxide-resistant mutant IB263. The constitutive peroxide response in
strain IB263 was shown to have resulted from a missense mutation at
codon 202 (GAT to GGT) of the oxyR gene
[oxyR(Con)] with a predicted D202G substitution in the
OxyR protein. Transcriptional fusion analysis revealed that deletion of
oxyR abolished the induction of ahpC and
katB following treatment with hydrogen peroxide or oxygen exposure. However, dps expression was induced approximately
fourfold by oxygen exposure in
oxyR strains but not by
hydrogen peroxide. This indicates that dps expression is
also under the control of an oxygen-dependent OxyR-independent
mechanism. Complementation of
oxyR mutant strains with
wild-type oxyR and oxyR(Con) restored the
inducible peroxide response and the constitutive response of the
ahpCF, katB, and dps genes,
respectively. However, overexpression of OxyR abolished the catalase
activity but not katB expression, suggesting that higher
levels of intracellular OxyR may be involved in other physiological
processes. Analysis of oxyR expression in the parents and
in
oxyR and overexpressing oxyR strains by Northern blotting and oxyR'::xylB
fusions revealed that B. fragilis OxyR does not control its
own expression.
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, East Carolina University School of
Medicine, Greenville, NC 27858-4354. Phone: (252) 816-3127. Fax: (252)
816-3535. E-mail: jsmith{at}brody.med.ecu.edu.
Journal of Bacteriology, September 2000, p. 5059-5069, Vol. 182, No. 18
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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