Changes in Microbial Community Composition and Geochemistry during Uranium and Technetium Bioimmobilization

Abstract

In a previous column study, we investigated the long-term impact of ethanol additions on U and Tc mobility in groundwater (M. M. Michalsen et al., Environ. Sci. Technol. 40:7048-7053, 2006). 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 analysis showed both an increase in microbial biomass (ϳ2 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-denaturing gradient gel electrophoresis 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 to 52%), while members of candidate division OP11 were dominant near the outlet (67%). Redundancy analysis revealed a highly significant difference (P ‫؍‬ 0.0003) between microbial community compositions within stimulated and control sediments, with geochemical variables explaining 68% of the variance in community composition on the first two canonical axes.In situ bioimmobilization has recently gained attention as a potentially effective remediation strategy for metal-or radionuclide-contaminated groundwater (4,29,39,65). During in situ bioimmobilization, electron donor additions are used to stimulate iron-and sulfate-reducing conditions, which promote the reductive precipitation of redox-sensitive metals and radionuclides from groundwater. Diverse or extreme geochemical conditions common to radionuclide-contaminated sites present unique challenges to successful implementation of bioimmobilization. One such site, located in Oak Ridge, TN, was established by the U.S. Department of Energy as a field research center (FRC). Groundwater at the FRC has a wide concentration range of U (up to 210 M), Tc (up to 24 nM), and nitrate (up to 168 mM), with pH varying from 3 to 7 (Environmental Remediation Sciences Program, Oak Ridge Field Research Center site descriptions [http://public.ornl.gov /nabirfrc/sitenarrative.cfm]).Several batch studies have been conducted to characterize the subsurface microbial community at the FRC and to evaluate its bioimmobilization potential with varied electron donors, geochemical conditions, and microbiological methods. In one study, contaminated FRC sediments were incubated with ethanol-amended, pH 4 site groundwater (53). Clone libraries of 16S rRNA genes indicated ...

How sulphate-reducing microorganisms cope with stress: lessons from systems biology

“…Analysis of the metagenome from the pristine area indicated the presence of sulphate-reducing deltaproteobacteria at low abundance, with the orders Desulfuromonadales and Myxococcales as the dominant deltaproteobacterial lineages. The elimination of nitrate stress by denitrification seemed to stimulate the growth of SRMs at the contaminated site 113,131,133,137,139 , in agreement with functional genomic studies that have shown that nitrate is a potent inhibitor of these organisms 39 . These results underscore the value of stress response analysis for improving the effective implementation of SRMs in biotechnological applications.…”

“…The local groundwater in the vicinity of the site contains one of the most concentrated mobile, subsurface uranium plumes in the United States. Numerous SRM species (particularly from the Deltaproteobacteria and the Firmicutes) have been detected at various locations within the FRC site 97,108,113,[127][128][129][130][131][132][133][134][135][136][137][138][139][140][141] , suggesting that SRMs have successfully adapted to this environment.…”

Bacterial community succession during in situ uranium bioremediation: spatial similarities along controlled flow paths

“…and Anaeromyxobacter spp. predominated in contaminated sediments following in situ biostimulation of microbial populations during push-pull tests (Petrie et al, 2003;North et al, 2004;Michalsen et al, 2007). However, different electron donors and engineering controls were used, and these comparisons also support the notion that there is an idiosyncratic relationship between population distribution and ecosystem process in terms of biostimulation for heavy metal reduction.…”

Partial Genome Assembly for a Candidate Division OP11 Single Cell from an Anoxic Spring (Zodletone Spring, Oklahoma)

“…As such, multiple diverse capabilities in different OP11 lineages or even within the same lineage are entirely possible. Indeed, a previous study enriching for anaerobes from an uranium-contaminated environment in field research center (FRC) sediments (Oak Ridge, TN) enriched for members of OP11 (GenBank accession numbers EF508021 and EF507960) during syntrophic growth on ethanol (46).…”