Bacterial Community Structure and Functional arrA Gene Diversity Associated with Arsenic Reduction and Release in an Industrially Contaminated Soil

This study aimed at evaluating potential arsenic (As) mobility in an industrially contaminated soil (64 mg/kg of As) 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 anaerobic conditions 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 were solubilized and mainly reduced to AsIII by indigenous soil microflora. After a 1-month incubation period in these biotic conditions, AsIII accounted for 80–85% of the total dissolved As and more than 60% of the solid-phase As. Bacterial community structure (i.e., 16S rDNA-based capillary electrophoresis single-strand conformation polymorphism profiles) changed with incubation time and As amendment. The detection of distantly related arsenate respiratory reductase genes (arrA), as functional markers of AsV respirers, indicates that novel dissimilatory AsV-reducing bacteria may be involved in As biotransformation and mobility in anoxic soils. Since As and iron were concomitantly released, a crucial 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 for heterotrophic AsV reduction to AsIII, which may increase As toxicity and mobility in the contaminated soils.