Multiple controls affect arsenite oxidase gene expression in Herminiimonas arsenicoxydans.
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 (sigma54) 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 sigma54-dependent promoter motif was identified upstream of aoxAB coding sequences.


CONCLUSIONS
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.
Koechler
Sandrine
S
UMR7156 Génétique Moléculaire, Génomique et Microbiologie, CNRS Université de Strasbourg, 28 rue Goethe, 67000 Strasbourg, France.
Cleiss-Arnold
Jessica
J
Proux
Caroline
C
Sismeiro
Odile
O
Dillies
Marie-Agnès
MA
Goulhen-Chollet
Florence
F
Hommais
Florence
F
Lièvremont
Didier
D
Arsène-Ploetze
Florence
F
Coppée
Jean-Yves
JY
Bertin
Philippe N
PN
D000595:Amino Acid Sequence; D018053:Arsenites / Q000378:metabolism / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D017124:Conserved Sequence; D020869:Gene Expression Profiling / Q000379:methods; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D053858:Metabolic Networks and Pathways; D008969:Molecular Sequence Data; D009154:Mutation; D009876:Operon; D042802:Oxalobacteraceae / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D053038:Quorum Sensing / Q000187:drug effects / Q000235:genetics; D016415:Sequence Alignment; D014158:Transcription, Genetic / Q000187:drug effects
D018053:Arsenites; D001426:Bacterial Proteins; D010088:Oxidoreductases; C078179:arsenite oxidase; C015001:arsenite