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Journal of Bacteriology, February 2006, p. 1081-1088, Vol. 188, No. 3
0021-9193/06/$08.00+0     doi:10.1128/JB.188.3.1081-1088.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Complex Regulation of Arsenite Oxidation in Agrobacterium tumefaciens

Des R. Kashyap,1 Lina M. Botero,1 William L. Franck,1 Daniel J. Hassett,2 and Timothy R. McDermott1*

Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, Montana 59717,1 Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-05242

Received 9 August 2005/ Accepted 9 November 2005

Seminal regulatory controls of microbial arsenite [As(III)] oxidation are described in this study. Transposon mutagenesis of Agrobacterium tumefaciens identified genes essential for As(III) oxidation, including those coding for a two-component signal transduction pair. The transposon interrupted a response regulator gene (referred to as aoxR), which encodes an ntrC-like protein and is immediately downstream of a gene (aoxS) encoding a protein with primary structural features found in sensor histidine kinases. The structural genes for As(III) oxidase (aoxAB), a c-type cytochrome (cytc2), and molybdopterin biosynthesis (chlE) were downstream of aoxR. The mutant could not be complemented by aoxSR in trans but was complemented by a clone containing aoxS-aoxR-aoxA-aoxB-cytc2 and consistent with reverse transcriptase (RT) PCR experiments, which demonstrated these genes are cotranscribed as an operon. Expression of aoxAB was monitored by RT-PCR and found to be up-regulated by the addition of As(III) to cell cultures. Expression of aoxAB was also controlled in a fashion consistent with quorum sensing in that (i) expression of aoxAB was absent in As(III)-unexposed early-log-phase cells but was observed in As(III)-unexposed, late-log-phase cells and (ii) treating As(III)-unexposed, early-log-phase cells with ethyl acetate extracts of As(III)-unexposed, late-log-phase culture supernatants also resulted in aoxAB induction. Under inducing conditions, aoxS expression was readily observed in the wild-type strain but significantly reduced in the mutant, indicating that AoxR is autoregulatory and at least partially controls the expression of the aox operon. In summary, regulation of A. tumefaciens As(III) oxidation is complex, apparently being controlled by As(III) exposure, a two-component signal transduction system, and quorum sensing.

* Corresponding author. Mailing address: Dept. of Land Resources and Environmental Sciences, Montana State University, Bozeman, MT 59717. Phone: (406) 994-2190. Fax: (406) 994-3933. E-mail: timmcder{at}montana.edu.

Journal of Bacteriology, February 2006, p. 1081-1088, Vol. 188, No. 3
0021-9193/06/$08.00+0     doi:10.1128/JB.188.3.1081-1088.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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