%0 Journal Article
%T Fermentation and Hydrogen Metabolism Affect Uranium Reduction by Clostridia
%A Weimin Gao
%A Arokiasamy J. Francis
%J ISRN Biotechnology
%D 2013
%R 10.5402/2013/657160
%X Previously, it has been shown that not only is uranium reduction under fermentation condition common among clostridia species, but also the strains differed in the extent of their capability and the pH of the culture significantly affected uranium(VI) reduction. In this study, using HPLC and GC techniques, metabolic properties of those clostridial strains active in uranium reduction under fermentation conditions have been characterized and their effects on capability variance of uranium reduction discussed. Then, the relationship between hydrogen metabolism and uranium reduction has been further explored and the important role played by hydrogenase in uranium(VI) and iron(III) reduction by clostridia demonstrated. When hydrogen was provided as the headspace gas, uranium(VI) reduction occurred in the presence of whole cells of clostridia. This is in contrast to that of nitrogen as the headspace gas. Without clostridia cells, hydrogen alone could not result in uranium(VI) reduction. In alignment with this observation, it was also found that either copper(II) addition or iron depletion in the medium could compromise uranium reduction by clostridia. In the end, a comprehensive model was proposed to explain uranium reduction by clostridia and its relationship to the overall metabolism especially hydrogen (H2) production. 1. Introduction Subsurface contamination by radionuclides and toxic metals is a major problem throughout the U.S. Department of Energy¡¯s (DOE¡¯s) complex; uranium contamination evokes particular environmental concern due to the high solubility and mobility of its oxidized form, U(VI). As physically removing the contaminated material is financially prohibitive, we need innovative, cost-effective in situ stabilization technologies that exploit the processes of natural attenuation. Recently, researchers at some DOE sites have assessed the microbial stabilization of actinides (U, Pu, and Np) and fission products (Tc) in subsurface environments, as in the uranium mill tailing remedial action (UMTRA) site in Rifle, CO (http://www.gjem.energy.gov/moab/) and at the Oak Ridge Field Research Centre (ORFRC) at Oak Ridge, TN (http://www.esd.ornl.gov/orifrc/). A wide variety of bacteria, including Desulfovibrio, Geobacter, and Shewanella, can couple the oxidation of organic compounds to the reduction of U(VI) and thus reductively precipitate uranium in its reduced form U(IV) [1¨C3]. Investigators have explored the mechanisms of uranium(VI) reduction by anaerobic bacteria [4¨C6]. Clostridia are anaerobic fermenting bacteria. They are gram-positive,
%U http://www.hindawi.com/journals/isrn.biotechnology/2013/657160/