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Journal of Bacteriology, February 2006, p. 842-851, Vol. 188, No. 3
0021-9193/06/$08.00+0     doi:10.1128/JB.188.3.842-851.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

ohrR and ohr Are the Primary Sensor/Regulator and Protective Genes against Organic Hydroperoxide Stress in Agrobacterium tumefaciens

Tatsanee Chuchue,1 Weerachai Tanboon,2 Benjaphorn Prapagdee,2,{dagger} James M. Dubbs,2 Paiboon Vattanaviboon,2* and Skorn Mongkolsuk1,2*

Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand,2 Department of Biotechnology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand1

Received 20 August 2005/ Accepted 8 November 2005

The genes involved in organic hydroperoxide protection in Agrobacterium tumefaciens were functionally evaluated. Gene inactivation studies and functional analyses have identified ohr, encoding a thiol peroxidase, as the gene primarily responsible for organic hydroperoxide protection in A. tumefaciens. An ohr mutant was sensitive to organic hydroperoxide killing and had a reduced capacity to metabolize organic hydroperoxides. ohr is located next to, and is divergently transcribed from, ohrR, encoding a sensor and transcription regulator of organic hydroperoxide stress. Transcription of both ohr and ohrR was induced by exposure to organic hydroperoxides but not by exposure to other oxidants. This induction required functional ohrR. The results of gel mobility shift and DNase I footprinting assays with purified OhrR, combined with in vivo promoter deletion analyses, confirmed that OhrR regulated both ohrR and ohr by binding to a single OhrR binding box that overlapped the ohrR and ohr promoters. ohrR and ohr are both required for the establishment of a novel cumene hydroperoxide-induced adaptive response. Inactivation or overexpression of other Prx family genes (prx1, prx2, prx3, bcp1, and bcp2) did not affect either the resistance to, or the ability to degrade, organic hydroperoxide. Taken together, the results of biochemical, gene regulation and physiological studies support the role of ohrR and ohr as the primary system in sensing and protecting A. tumefaciens from organic hydroperoxide stress.

* Corresponding author. Mailing address: Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand. Phone: 662-574-0622, x1402. Fax: 662-574-2027. E-mail for S. Mongkolsuk: skorn{at}cri.or.th. E-mail for P. Vattanaviboon: paiboon{at}cri.or.th.

{dagger} Present address: Faculty of Environment and Resource Studies, Mahidol University, Nakornpathom 73170, Thailand.

Journal of Bacteriology, February 2006, p. 842-851, Vol. 188, No. 3
0021-9193/06/$08.00+0     doi:10.1128/JB.188.3.842-851.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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