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Thioredoxin reductase is essential for thiol/disulfide redox control and oxidative stress survival of the anaerobe Bacteroides fragilis.

ABSTRACT: Results of this study showed that the anaerobic, opportunistic pathogen Bacteroides fragilis lacks the glutathione/glutaredoxin redox system and possesses an extensive number of putative thioredoxin (Trx) orthologs. Analysis of the genome sequence revealed six Trx orthologs and an absence of genes required for synthesis of glutathione and glutaredoxins. In addition, it was shown that the thioredoxin reductase (TrxB)/Trx system is the major or sole redox system for thiol/disulfide cellular homeostasis in this anaerobic bacterium. Expression of the B. fragilis trxB gene was induced following treatment with diamide or H(2)O(2) or exposure to oxygen. This inducible trxB expression was OxyR independent. Northern blot hybridization analysis showed that the trxB mRNA was cotranscribed with lolA as a bicistronic transcript or was present as a monocistronic transcript that was also highly induced under the same conditions. The role of LolA, a prokaryotic periplasmic lipoprotein-specific molecular chaperone in the thiol/disulfide redox system, is unknown. A trxB deletion mutant was more sensitive to the effects of diamide and oxygen than the parent strain. In addition, the trxB mutant was unable to grow in culture media without addition of a reductant. Furthermore, the trxB mutant was not able to induce intraabdominal abscess formation in a mouse model, whereas the parent strain was. Taken together, these data strongly suggest that TrxB/Trx is the major, if not the sole, thiol/disulfide redox system in this anaerobe required for survival and abscess formation in a peritoneal cavity infection model.

SUBMITTER: Rocha ER

PROVIDER: S-EPMC2168685 | biostudies-literature | 2007 Nov

REPOSITORIES: biostudies-literature

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Thioredoxin reductase is essential for thiol/disulfide redox control and oxidative stress survival of the anaerobe Bacteroides fragilis.

Rocha Edson R ER Tzianabos Arthur O AO Smith C Jeffrey CJ

Journal of bacteriology 20070914 22

Results of this study showed that the anaerobic, opportunistic pathogen Bacteroides fragilis lacks the glutathione/glutaredoxin redox system and possesses an extensive number of putative thioredoxin (Trx) orthologs. Analysis of the genome sequence revealed six Trx orthologs and an absence of genes required for synthesis of glutathione and glutaredoxins. In addition, it was shown that the thioredoxin reductase (TrxB)/Trx system is the major or sole redox system for thiol/disulfide cellular homeos ...[more]

PMID: 17873045

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Project description: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 DeltaoxyR 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 DeltaoxyR 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 DeltaoxyR and overexpressing oxyR strains by Northern blotting and oxyR'::xylB fusions revealed that B. fragilis OxyR does not control its own expression.

Dataset Information

Thioredoxin reductase is essential for thiol/disulfide redox control and oxidative stress survival of the anaerobe Bacteroides fragilis.

Publications

Thioredoxin reductase is essential for thiol/disulfide redox control and oxidative stress survival of the anaerobe Bacteroides fragilis.

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