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Appl. Environ. Microbiol. doi:10.1128/AEM.00309-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Changes in Microbial Community Composition and Geochemistry During Uranium and Technetium Bio-Immobilization

Department of Civil Engineering, Oregon State University, Corvallis, OR 97331; Center for Biomarker Analysis, University of Tennessee, Knoxville, TN 37932; Department of Botany and Microbiology, University of Oklahoma, Norman, OK 73019

^* To whom correspondence should be addressed. Email: mandy.michalsen{at}gmail.com.

	Abstract

In a previous column study, we investigated the long-term impact of ethanol additions on U and Tc mobility in groundwater (Michalsen et al., Environ. Sci. Technol. 2006, 40:7048-7053). Ethanol additions stimulated iron- and sulfate-reducing conditions and significantly enhanced U and Tc removal from groundwater compared to an identical column that received no ethanol additions (control). Here we present the results of a combined signature lipid and nucleic acid-based microbial community characterization in sediments collected from along the ethanol stimulated and control column flow paths. Phospholipid fatty acid (PLFA) analysis showed both an increase in microbial biomass (2 orders of magnitude) and decreased ratios of cyclopropane to monoenoic precursor fatty acids in the stimulated column compared to the control, which is consistent with electron donor limitation in the control. Spatial shifts in microbial community composition were identified by PCR-DGGE analysis as well as by quantitative-PCR, which showed that Geobacteraceae increased significantly near the stimulated column outlet where soluble electron acceptors were largely depleted. Clone libraries of 16S rRNA genes from selected flow path locations in the stimulated column showed that Proteobacteria were dominant near the inlet (46-52%), while members of the candidate division OP11 were dominant near the outlet (67%). Redundancy analysis revealed a highly significant difference (p=0.0003) between microbial community composition within stimulated and control sediments, with geochemical variables explaining 68% of the variance in community composition on the first two canonical axes.