This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowReprints and Permissions
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Branco, R.
Right arrow Articles by Zhitkovich, A.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Branco, R.
Right arrow Articles by Zhitkovich, A.

 Previous Article  |  Next Article 

Journal of Bacteriology, November 2008, p. 6996-7003, Vol. 190, No. 21
0021-9193/08/$08.00+0     doi:10.1128/JB.00289-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Chromate-Inducible chrBACF Operon from the Transposable Element TnOtChr Confers Resistance to Chromium(VI) and Superoxide{triangledown}

Rita Branco,1,2 Ana Paula Chung,1 Tatiana Johnston,2 Volkan Gurel,2 Paula Morais,1* and Anatoly Zhitkovich2*

Laboratorio de Microbiologia, Departmento de Bioquimica, Universidade de Coimbra, 3001-517 Coimbra, Portugal,1 Department of Pathology and Laboratory Medicine, Brown University, 70 Ship Street, Providence, Rhode Island 029122

Received 26 February 2008/ Accepted 25 August 2008

Large-scale industrial use of chromium(VI) has resulted in widespread contamination with carcinogenic chromium(VI). The abilities of microorganisms to survive in these environments and to detoxify chromate require the presence of specific resistance systems. Here we report identification of the transposon-located (TnOtChr) chromate resistance genes from the highly tolerant strain Ochrobactrum tritici 5bvl1 surviving chromate concentrations of >50 mM. The 7,189-bp-long TnOtChr of the mixed Tn21/Tn3 transposon subfamily contains a group of chrB, chrA, chrC, and chrF genes situated between divergently transcribed resolvase and transposase genes. The chrB and chrA genes, but not chrF or chrC, were essential for establishment of high resistance in chromium-sensitive O. tritici. The chr promoter was strongly induced by chromate or dichromate, but it was completely unresponsive to Cr(III), oxidants, sulfate, or other oxyanions. Plasmid reporter experiments identified ChrB as a chromate-sensing regulator of chr expression. Induction of the chr operon suppressed accumulation of cellular Cr through the activity of a chromate efflux pump encoded by chrA. Expression of chrB, chrC, or chrF in an Escherichia coli sodA sodB double mutant restored its aerobic growth in minimal medium and conferred resistance to superoxide-generating agents menadione and paraquat. Nitroblue tetrazolium staining on native gels showed that ChrC protein had superoxide dismutase activity. TnOtChr appears to represent a mobile genetic system for the distribution of the chromate-regulated resistance operon. The presence of three genes protecting against superoxide toxicity should provide an additional survival advantage to TnOtChr-containing cells in the environments with multiple redox-active contaminants.

* Corresponding author. Mailing address for Paula Morais: Laboratorio de Microbiologia, Departmento de Bioquimica, Universidade de Coimbra, 3001-517 Coimbra, Portugal. Phone: 351-239-824024. E-mail: pvmorais{at}ci.uc.pt. Mailing address for Anatoly Zhitkovich: Department of Pathology and Laboratory Medicine, Brown University, 70 Ship Street, Providence, RI 02912. Phone: (401) 863-2912. Fax: (401) 863-9008. E-mail: anatoly_zhitkovich{at}brown.edu

{triangledown} Published ahead of print on 5 September 2008.

Journal of Bacteriology, November 2008, p. 6996-7003, Vol. 190, No. 21
0021-9193/08/$08.00+0     doi:10.1128/JB.00289-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Diaz-Magana, A., Aguilar-Barajas, E., Moreno-Sanchez, R., Ramirez-Diaz, M. I., Riveros-Rosas, H., Vargas, E., Cervantes, C. (2009). Short-Chain Chromate Ion Transporter Proteins from Bacillus subtilis Confer Chromate Resistance in Escherichia coli. J. Bacteriol. 191: 5441-5445 [Abstract] [Full Text]  


Copyright © 2009 by the American Society for Microbiology.   For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»