Background: Anthropogenic use of uranium has resulted in over 120 contaminated sites in the United States alone. Reductive precipitation of U(VI) by stimulating indigenous microorganisms dramatically decreases uranium solubility and is an attractive, low-cost bioremediation strategy. Our previous long-term sediment studies demonstrated that after an initial period of U(VI) reduction and immobilization significant reoxidation of U(IV) and remobilization of U(VI) occurred.