Arsenic Mobilization and Dissimilatory Arsenate Respiring Bacteria in Landfill Sediments.

Naturally occurring arsenic in aquifer solids and the microbial reduction of arsenate to arsenite is one of the important mechanisms resulting in groundwater contamination. Anaerobic microcosms were constructed with three aquifer solids (oxidized, reduced and intermediate sites) collected from an area near the Logan City landfill, UT. Groundwater and groundwater with the addition of glucose were added to the microcosms and analyzed over time to evaluate the role of dissimilatory arsenate respiring bacteria (DARB) in arsenic mobilization.  Though, addition of glucose significantly increased arsenic solubilization in oxidized aquifer material, it decreased arsenic mobilization in reduced aquifer solids. Concurrently DARB in the aquifer solids were detected using arsenate respiratory reductase (arr) gene as the target in real-time PCR; the arrA gene copy numbers were greater in glucose added oxidized aquifer solids compared to reduced  aquifer solids where arrA genes could not be quantified.   A nested PCR approach was used to amplify arrA genes from these microcosm samples and was cloned to make arrA gene libraries. Phylogenetic analysis of the arrA gene showed that microbial community structure differed with sediments and carbon addition. Thus, using molecular tools we were able to better understand the significance of DARB  and arsenic solubilization in this aquifer system.