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Appl. Environ. Microbiol. doi:10.1128/AEM.00531-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The Agrobacterium tumefaciens fur has important physiological roles in iron and manganese homeostasis, oxidative stress response and full virulence

Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand, Post Graduate Training and Research Program in Environmental Science, Technology and Management, Asia Institute of Technology, Pathumthani 12120, Thailand, Department of Biotechnology, Faculty of Sciences, Mahidol University, Bangkok 10400, Thailand

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

	Abstract

In Agrobacterium tumefaciens, the balance between acquiring enough iron and avoiding iron-induced toxicity is regulated in part by Fur (ferric uptake regulator). A fur mutant was constructed to address the physiological role of the regulator. Atypically, the mutant did not show alterations in levels of siderophore biosynthesis and expression of iron transport genes. However, the fur mutant was more sensitive than a wild-type to an iron chelator, 2,2'-dipyridyl, and was also more resistant to an iron-activated antibiotic, streptonigrin, suggesting that Furhas a role in regulating iron concentrations. A. tumefaciens sitA, the periplasmic binding protein of a putative ABC-type iron and manganese transport system (sitABCD), was strongly repressed by Mn²⁺ and, to a lesser extent, by Fe²⁺ and this regulation was Fur-dependent. Moreover, the fur mutant was more sensitive to manganese than wild-type. This was consistent with the fact that fur mutant was constitutive up-expression of the manganese uptake sit operon. Fur_At showed a regulatory role under iron-limiting conditions. Furthermore, Fur has a role in determining oxidative resistance levels. The fur mutant was hypersensitive to hydrogen peroxide and had reduced catalase activity. The virulence assay showed that the fur mutant had a reduced ability to cause tumors on tobacco leaves compared to wild-type NTL4.