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Applied and Environmental Microbiology, June 2008, p. 3718-3729, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.02308-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Microbial Communities in Contaminated Sediments, Associated with Bioremediation of Uranium to Submicromolar Levels

Erick Cardenas,¹ Wei-Min Wu,² Mary Beth Leigh,^1, Jack Carley,³ Sue Carroll,³ Terry Gentry,^3, Jian Luo,^2,# David Watson,³ Baohua Gu,³ Matthew Ginder-Vogel,^2, Peter K. Kitanidis,² Philip M. Jardine,³ Jizhong Zhou,^3,¶ Craig S. Criddle,² Terence L. Marsh,^1* and James M. Tiedje^1*

Center for Microbial Ecology, Michigan State University, East Lansing, Michigan 48824,¹ Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305-4020,² Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831³

Received 12 October 2007/ Accepted 18 April 2008

Microbial enumeration, 16S rRNA gene clone libraries, and chemical analysis were used to evaluate the in situ biological reduction and immobilization of uranium(VI) in a long-term experiment (more than 2 years) conducted at a highly uranium-contaminated site (up to 60 mg/liter and 800 mg/kg solids) of the U.S. Department of Energy in Oak Ridge, TN. Bioreduction was achieved by conditioning groundwater above ground and then stimulating growth of denitrifying, Fe(III)-reducing, and sulfate-reducing bacteria in situ through weekly injection of ethanol into the subsurface. After nearly 2 years of intermittent injection of ethanol, aqueous U levels fell below the U.S. Environmental Protection Agency maximum contaminant level for drinking water and groundwater (<30 µg/liter or 0.126 µM). Sediment microbial communities from the treatment zone were compared with those from a control well without biostimulation. Most-probable-number estimations indicated that microorganisms implicated in bioremediation accumulated in the sediments of the treatment zone but were either absent or in very low numbers in an untreated control area. Organisms belonging to genera known to include U(VI) reducers were detected, including Desulfovibrio, Geobacter, Anaeromyxobacter, Desulfosporosinus, and Acidovorax spp. The predominant sulfate-reducing bacterial species were Desulfovibrio spp., while the iron reducers were represented by Ferribacterium spp. and Geothrix spp. Diversity-based clustering revealed differences between treated and untreated zones and also within samples of the treated area. Spatial differences in community structure within the treatment zone were likely related to the hydraulic pathway and to electron donor metabolism during biostimulation.

Published ahead of print on 2 May 2008.

Present address: Institute of Arctic Biology, University of Alaska—Fairbanks, Fairbanks, AK 99775.

Present address: Soil & Crop Sciences Department, Texas A&M University, College Station, TX 77843-2474.

^# Present address: Department of Civil & Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332.

Present address: Center for Critical Zone Research, Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19711.

^¶ Present address: Department of Botany and Microbiology, University of Oklahoma, Norman, OK 73019.