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Journal of Bacteriology, April 2009, p. 2083-2090, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01380-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Roles of Agrobacterium tumefaciens RirA in Iron Regulation, Oxidative Stress Response, and Virulence{triangledown}

Patchara Ngok-Ngam,1 Nantaporn Ruangkiattikul,2 Aekkapol Mahavihakanont,1 Susan S. Virgem,3 Rojana Sukchawalit,4,5* and Skorn Mongkolsuk1,4

Department of Biotechnology, Faculty of Sciences, Mahidol University, Bangkok 10400, Thailand,1 Environmental Toxicology, Chulabhorn Graduate Institute, Lak Si, Bangkok 10210, Thailand,2 Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139,3 Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand,4 Applied Biological Sciences, Chulabhorn Graduate Institute, Lak Si, Bangkok 10210, Thailand5

Received 2 October 2008/ Accepted 9 January 2009

The analysis of genetics and physiological functions of Agrobacterium tumefaciens RirA (rhizobial iron regulator) has shown that it is a transcription regulator and a repressor of iron uptake systems. The rirA mutant strain (NTLrirA) overproduced siderophores and exhibited a highly constitutive expression of genes involved in iron uptake (fhuA, irp6A, and fbpA) compared to that of the wild-type strain (NTL4). The deregulation in the iron control of iron uptake in NTLrirA led to iron overload in the cell, which was supported by the observation that the NTLrirA mutant was more sensitive than wild-type NTL4 to an iron-activated antibiotic, streptonigrin. The NTLrirA mutant was more sensitive than the parental strain to oxidants, including hydrogen peroxide, organic hydroperoxide, and a superoxide generator, menadione. However, the addition of an iron chelator, 2,2'-dipyridyl, reversed the mutant hypersensitivity to H2O2 and organic hydroperoxide, indicating the role of iron in peroxide toxicity. Meanwhile, the reduced level of superoxide dismutase (SodBIII) was partly responsible for the menadione-sensitive phenotype of the NTLrirA mutant. The NTLrirA mutant showed a defect in tumorigenesis on tobacco leaves, which likely resulted from the increased sensitivity of NTLrirA to oxidants and the decreased ability of NTLrirA to induce virulence genes (virB and virE). These data demonstrated that RirA is important for A. tumefaciens during plant-pathogen interactions.

* Corresponding author. Mailing address: Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand. Phone: 66 (2) 5740622, ext. 3804. Fax: 66 (2) 5742027. E-mail: rojana{at}cri.or.th

{triangledown} Published ahead of print on 23 January 2009.

Journal of Bacteriology, April 2009, p. 2083-2090, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01380-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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