Bacterial community structure and functional arrAgene diversity associated with arsenic reductionand release in an industrially contaminated soil

International audience; This study aimed at evaluating potential arsenic (As) mobility in an industrially contaminatedsoil (64 mg As kg-1) of the Meuse River basin, and at identifying key bacterial groups that drive soil As dynamics. Both speciation and release of As from this soil was followed under anaerobicconditions using a laboratory batch experiment. In the presence of exogenous carbon sources,AsV initially present in the soil matrix and/or adsorbed on synthetic hydrous ferric oxides wassolubilized and mainly reduced into AsIII by indigenous soil microfora. After a one-monthincubation period in these biotic conditions, AsIII accounted for 80-85% of the total dissolved Asand more than 60% of the solid-phase As. Bacterial community structure (i.e. 16S rDNA-basedCE-SSCP profiles) changed with incubation time and As amendment. The detection of distantlyrelated arsenate respiratory reductase genes (arrA), as functional markers of AsV-respirers,indicates that novel dissimilatory AsV-reducing bacteria may be involved in Asbiotransformation and mobility in anoxic soils. Since As and iron were concomitantly released, acrucial role of indirect As-mobilizing bacteria on As behavior was also revealed. Our results show that the majority of As within the soil matrix was bioavailable and bioaccessible forheterotrophic AsV reduction to AsIII, which may increase As toxicity and mobility in thecontaminated soils.