Potential arsenate reduction of bacteria isolated from a iron-arsenic co-precipitation product

Due to its frequent occurrence in the environment and to its high toxicity, arsenic (As) is the first among the toxic elements listed by the Agency for Toxic Substances and Diseases Registry (ATSDR). Arsenic contamination is a dramatic problem in many Countries around the world, especially in Bangladesh. The most common oxidation states of arsenic in environment are the pentavalent As(V) and the trivalentAs(III), more mobile and more toxic. As(V) adsorbs to the surface of minerals such as ferrihydrite and alumina or co-precipitates with iron oxides. In As-rich waters, such as in Bangladesh groundwaters, high concentrations of dissolved metals can be found, and the formation of co-precipitation products is documented. The microbial communities that can develop in such As-rich substrates are directly or indirectly involved in regulating As mobility. Bacteria can enhance the production of co-precipitation products mediating As or iron oxidation. The presence of As (or iron) reducing microrganisms, on the contrary, could promote an enhancement of the As mobility. The aim of this study was to evaluate the potential of As (V) reduction to As(III) of bacterial isolates from a iron-arsenic co-precipitation product sampled from a tank for groundwater storage in Satkhira District, south-west Bangladesh. We evaluate the ability of such isolates to produce As(III) in laboratory experiment with different amounts of As(V) and nutrient inputs. We tested both aerobic and sub-oxic incubation conditions. No bacteria were isolated that could utilize As(V) as electron acceptor, under the respective growth conditions tested, but 26 morphologically distinct arsenic-resistant heterotrophic bacteria were isolated that could grow in the presence of high concentrations of As(V) and that could release As(III) via detoxification pathway. Analysis of the 16S rRNA gene sequence of these bacteria revealed that the isolate that reduced As(V) to As(III) more efficiently respect with to others in each experimental condition tested belong to genus Acinetobacter.