RESEARCH ARTICLE Microbial communities biostimulated by ethanol during uranium (VI) bioremediation in contaminated sediment as shown by stable isotope probing Mary Beth LEIGH (✉) 1,2 , Wei-Min WU (✉) 3 , Erick CARDENAS 1 , Ondrej UHLIK 4 , Sue CARROLL 5 , Terry GENTRY 5,7 , Terence L. MARSH 1 , Jizhong ZHOU 5,6 , Philip JARDINE 5 , Craig S. CRIDDLE 3 , James M. TIEDJE 1 1 Center for Microbial Ecology, Michigan State University, East Lansing, MI 48824, USA 2 Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 99775, USA 3 Department of Civil and Environmental Engineering, Center for Sustainable Development & Global Competitiveness, Codiga Resource Recovery Center, Stanford University, Stanford, CA 94305-4020, USA 4 Department of Biochemistry and Microbiology, Institute of Chemical Technology Prague, Technicka 3, 166 28 Prague, Czech Republic 5 Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA 6 Department of Botany and Microbiology, University of Oklahoma, Norman, OK 73019, USA 7 Department of Crop and Soil Sciences, Texas A&M University, College Station, TX 77843, USA © Higher Education Press and Springer-Verlag Berlin Heidelberg 2014 Abstract Stable isotope probing (SIP) was used to identify microbes stimulated by ethanol addition in microcosms containing two sediments collected from the bioremediation test zone at the US Department of Energy Oak Ridge site, TN, USA. One sample was highly bioreduced with ethanol while another was less reduced. Microcosms with the respective sediments were amended with 13 C labeled ethanol and incubated for 7 days for SIP. Ethanol was rapidly converted to acetate within 24 h accompanied with the reduction of nitrate and sulfate. The accumulation of acetate persisted beyond the 7 d period. Aqueous U did not decline in the microcosm with the reduced sediment due to desorption of U but continuously declined in the less reduced sample. Microbial growth and concomitant 13 C-DNA production was detected when ethanol was exhausted and abundant acetate had accumu- lated in both microcosms. This coincided with U(VI) reduction in the less reduced sample. 13 C originating from ethanol was ultimately utilized for growth, either directly or indirectly, by the dominant microbial community members within 7 days of incubation. The microbial community was comprised predominantly of known denitrifiers, sulfate-reducing bacteria and iron (III) redu- cing bacteria including Desulfovibrio, Sphingomonas, Ferribacterium, Rhodanobacter, Geothrix, Thiobacillus and others, including the known U(VI)-reducing bacteria Acidovorax, Anaeromyxobacter, Desulfovibrio, Geobac- ter and Desulfosporosinus. The findings suggest that ethanol biostimulates the U(VI)-reducing microbial com- munity by first serving as an electron donor for nitrate, sulfate, iron (III) and U(VI) reduction, and acetate which then functions as electron donor for U(VI) reduction and carbon source for microbial growth. Keywords Stable isotope probing (SIP), ethanol, acetate, uranium reduction, sediment, bioremediation 1 Introduction Uranium contamination of groundwater has been observed at many sites around the world. Uranium is listed as a groundwater contaminant at US Department of Energy (DOE) sites, and poses risks for liver damage and cancer. In early 1990s, bioreduction of mobile U(VI) to sparingly soluble and immobile U(IV) was proposed to be a promising approach to remediate U in situ [1]. Field tests for bioreduction and immobilization of uranium in contaminated aquifers and sediments have been performed [2–4]. During February 2004 to December 2008, a pilot scale in situ bioremediation system was implemented at the Field Research Center (FRC), Oak Ridge, Tennessee, USA, which established hydraulic control, conditioned groundwater and biostimulated indigenous microorgan- isms to reduce U(VI) to U(IV), rendering it immobile [5,6] Received November 28, 2013; accepted April 18, 2014 E-mail: mbleigh@alaska.edu, wei-min.wu@stanford.edu Front. Environ. Sci. Eng. 2015, 9(3): 453–464 DOI 10.1007/s11783-014-0721-6