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Journal of Bacteriology, May 2009, p. 3384-3391, Vol. 191, No. 10
0021-9193/09/$08.00+0     doi:10.1128/JB.01665-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Thioredoxins in Redox Maintenance and Survival during Oxidative Stress of Bacteroides fragilis{triangledown} ,{dagger}

Michael A. Reott, Anita C. Parker, Edson R. Rocha, and C. Jeffrey Smith*

Department of Microbiology and Immunology, East Carolina University, Brody School of Medicine, 600 Moye Blvd., Greenville, North Carolina 27834

Received 26 November 2008/ Accepted 2 March 2009

The anaerobe Bacteroides fragilis is a gram-negative, opportunistic pathogen that is highly aerotolerant and can persist in aerobic environments for extended periods. In this study, the six B. fragilis thioredoxins (Trxs) were investigated to determine their role during oxidative stress. Phylogenetic analyses of Trx protein sequences indicated that four of the six Trxs (TrxA, TrxC, TrxD, and TrxF) belong to the M-type Trx class but were associated with two different M-type lineages. TrxE and TrxG were most closely associated to Y-type Trxs found primarily in cyanobacteria. Single and multiple trx gene deletions were generated to determine functional differences between the Trxs. The trxA gene was essential, but no anaerobic growth defects were observed for any other single trx deletion or for the {Delta}trxC {Delta}trxD::cfxA {Delta}trxE {Delta}trxF {Delta}trxG quintuple mutant. Regulation of the trx genes was linked to the oxidative stress response, and all were induced by aerobic conditions. The {Delta}trxC {Delta}trxE {Delta}trxF {Delta}trxG and the {Delta}trxC {Delta}trxD::cfxA {Delta}trxE {Delta}trxF {Delta}trxG multiple deletion strains were impaired during growth in oxidized media, but single trx gene mutants did not have a phenotype in this assay. TrxD was protective during exposure to the thiol oxidant diamide, and expression of trxD was induced by diamide. Diamide-induced expression of trxC, trxE, and trxF increased significantly in a trxD mutant strain, suggesting that there is some capacity for compensation in this complex Trx system. These data provide insight into the role of individual Trxs in the B. fragilis oxidative stress response.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, 600 Moye Blvd., Greenville, NC 27834. Phone: (252) 744-2700. Fax: (252) 744-3104. E-mail: smithcha{at}ecu.edu

{triangledown} Published ahead of print on 13 March 2009.

{dagger} Supplemental material for this article is available at http://jb.asm.org/.

Journal of Bacteriology, May 2009, p. 3384-3391, Vol. 191, No. 10
0021-9193/09/$08.00+0     doi:10.1128/JB.01665-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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