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

Abstract

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 g/liter or 0.126 M). 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. Diversitybased 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.

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

“…were the most abundant genus in the biostimulated zone (Cardenas et al, 2008), and our results with groundwater also showed a predominance of Desulfovibrio sequences at this time period. The Cardenas et al (2008) study also detected Desulfosporosinus, Geobacter, Anaeromyxobacter, Geothrix and Acidovorax related sequences associated with the sediment, and similar sequences were detected in our temporal study of the groundwater albeit at different proportions. These results suggested that some predominant populations might inhabit both the solid and aqueous phases (for example, Desulfovibrio), whereas others might be exclusive to solid phases (for example, Acidobacteriaceae).…”

“…have been isolated from a hydrocarbon-contaminated aquifer (Coates et al, 1999) and were also enriched when exposed to petroleum compounds in laboratory experiments (Abed et al, 2002). Geothrixlike sequences were also detected in the stimulated treatment zones of FRC sediments (Cardenas et al, 2008). Geobacter spp.…”

Structural Similarities between Biogenic Uraninites Produced by Phylogenetically and Metabolically Diverse Bacteria

“…However, Shewanella has not been found to be a prevalent DMRB during biostimulation at contaminated sites (9,17,18). For example, subsurface ethanol amendments enriched populations of DMRB and DSRB at Oak Ridge, TN.…”

“…For example, subsurface ethanol amendments enriched populations of DMRB and DSRB at Oak Ridge, TN. Dominant genera were identified as Ferribacterium, Geothrix, and Desulfovibrio and to a lesser degree Geobacter, Anaeromyxobacter, Desulfosporosinus, and Acidovorax (17). During acetate amendment of a uranium-contaminated site in Rifle, CO, the community dynamically shifted from Geobacteraceae family DMRB to Desulfobacteraceae family DSRB in regions where bioavailable Fe(III) was consumed (9,18).…”

16S rRNA Gene Microarray Analysis of Microbial Communities in Ethanol-Stimulated Subsurface Sediment

“…Information on the status of microbial communities involved in U(VI) reduction and other electron-accepting pathways is important to understand the spatial/temporal dynamics and overall efficacy of in situ uranium bioremediation (1). Although 16S rRNA clone libraries and/or microarrays have been applied to various U(VI) reduction systems (2,4,7,17,28,29,40,41,44), knowledge remains scant of the quantitative coverage of these techniques, particularly in situations where multiple groups of organisms are active.…”