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J. Bacteriol. doi:10.1128/JB.00960-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Multiple superoxide dismutases in Agrobacterium tumefaciens: functional analysis, gene regulation and their influence on tumoriogenesis

Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand; Department of Biotechnology, and Centre of Emerging Bacterial Infection, Faculty of Science, Mahidol University, Bangkok 10400, Thailand; Department of Microbiology, University of Illinois at Urbana-Campaign, Urbana, Illinois 61801, USA

^* To whom correspondence should be addressed. Email: skorn{at}cri.or.th.

	Abstract

Agrobacterium tumefaciens possesses three iron containing superoxide dismutases (FeSods) encoded by distinct genes with differential expression patterns. SodBI and SodBII are cytoplasmic isozymes while SodBIII is a periplasmic isozyme. sodBI is expressed at a high levels throughout all growth phases. sodBII expression is highly induced upon exposure to superoxide anions in a SoxR dependent manner. sodBIII is only expressed during stationary phase. Analysis of the physiological function of sods reveals that inactivation of sodBI markedly reduced levels of resistance to a superoxide generator, menadione. A mutant lacks all three Sod enzymes is the most sensitive to menadione treatment indicating that all sods contribute at varying levels towards the overall menadione resistance level. Sods also have important roles in A. tumefaciens virulence toward a host plant. A sodBI but not sodBII or sodBIII mutant showed marked reduction in its ability to induce tumors on tobacco leaf discs while the triple sod null mutant is avirulence.

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