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Open Access Research article

Multiple controls affect arsenite oxidase gene expression in Herminiimonas arsenicoxydans

Sandrine Koechler1, Jessica Cleiss-Arnold1, Caroline Proux2, Odile Sismeiro2, Marie-Agnès Dillies2, Florence Goulhen-Chollet1, Florence Hommais3, Didier Lièvremont1, Florence Arsène-Ploetze1, Jean-Yves Coppée2 and Philippe N Bertin1*

Author Affiliations

1 UMR7156 Génétique Moléculaire, Génomique et Microbiologie, CNRS Université de Strasbourg, 28 rue Goethe, 67000 Strasbourg, France

2 Plate-forme technologique Puces à ADN, Institut Pasteur, 28 rue du Dr. Roux, 75724 Paris cedex 15, France

3 UMR5240 Microbiologie, Adaptation et Pathogénie, CNRS Université Lyon 1, Bâtiment André Lwoff, 10 rue Dubois, 69622 Villeurbanne cedex France

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BMC Microbiology 2010, 10:53  doi:10.1186/1471-2180-10-53

Published: 18 February 2010

Abstract

Background

Both the speciation and toxicity of arsenic are affected by bacterial transformations, i.e. oxidation, reduction or methylation. These transformations have a major impact on environmental contamination and more particularly on arsenic contamination of drinking water. Herminiimonas arsenicoxydans has been isolated from an arsenic- contaminated environment and has developed various mechanisms for coping with arsenic, including the oxidation of As(III) to As(V) as a detoxification mechanism.

Results

In the present study, a differential transcriptome analysis was used to identify genes, including arsenite oxidase encoding genes, involved in the response of H. arsenicoxydans to As(III). To get insight into the molecular mechanisms of this enzyme activity, a Tn5 transposon mutagenesis was performed. Transposon insertions resulting in a lack of arsenite oxidase activity disrupted aoxR and aoxS genes, showing that the aox operon transcription is regulated by the AoxRS two-component system. Remarkably, transposon insertions were also identified in rpoN coding for the alternative N sigma factor (σ54) of RNA polymerase and in dnaJ coding for the Hsp70 co-chaperone. Western blotting with anti-AoxB antibodies and quantitative RT-PCR experiments allowed us to demonstrate that the rpoN and dnaJ gene products are involved in the control of arsenite oxidase gene expression. Finally, the transcriptional start site of the aoxAB operon was determined using rapid amplification of cDNA ends (RACE) and a putative -12/-24 σ54-dependent promoter motif was identified upstream of aoxAB coding sequences.

Conclusion

These results reveal the existence of novel molecular regulatory processes governing arsenite oxidase expression in H. arsenicoxydans. These data are summarized in a model that functionally integrates arsenite oxidation in the adaptive response to As(III) in this microorganism.