Microbial incorporation of 13C-labeled acetate at the field scale: detection of microbes responsible for reduction of U(VI).
ABSTRACT A field-scale acetate amendment experiment was performed in a contaminated aquifer at Old Rifle, CO to stimulate in situ microbial reduction of U(VI) in groundwater. To evaluate the microorganisms responsible for microbial uranium reduction during the experiment, 13C-labeled acetate was introduced into well bores via bio-traps containing porous activated carbon beads (Bio-Sep). Incorporation of the 13C from labeled acetate into cellular DNA and phospholipid fatty acid (PLFA) biomarkers was analyzed in parallel with geochemical parameters. An enrichment of active sigma-proteobacteria was demonstrated in downgradient monitoring wells: Geobacter dominated in wells closer to the acetate injection gallery, while various sulfate reducers were prominent in different downgradient wells. These results were consistent with the geochemical evidence of Fe(III), U(VI), and SO(4)2- reduction. PLFA profiling of bio-traps suspended in the monitoring wells also showed the incorporation of 13C into bacterial cellular lipids. Community composition of downgradient monitoring wells based on quinone and PLFA profiling was in general agreement with the 13C-DNA result. The direct application of 13C label to biosystems, coupled with DNA and PLFA analysis,
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ABSTRACT: The effect of phenol concentration on phenol biodegradation at an industrial site in the south of Wales, United Kingdom, was investigated using standard Bio-Sep® Bio-Traps® and Bio-Traps® coupled with stable isotope probing (SIP). Unlike many 13C-amendments used in SIP studies (such as hydrocarbons) that physically and reversibly adsorb to the activated carbon component of the Bio-Sep® beads, phenol is known to irreversibly chemisorb to activated carbon. Bio-Traps® were deployed for 32 days in nine site groundwater monitoring wells representing a wide range of phenol concentrations. Bio-Traps® amended with 13C-phenol were deployed together with non-amended Bio-Traps® in three wells. Quantitative polymerase chain reaction (qPCR) analysis of Bio-Traps® post-deployment indicated an inhibitory effect of increasing phenol concentration on both total eubacteria and aerobic phenol-utilizing bacteria as represented by the concentration of phenol hydroxylase gene. Despite the chemisorption of phenol to the Bio-Sep® beads, activated carbon stable isotope analysis showed incorporation of 13C into biomass and dissolved inorganic carbon (DIC) in each SIP Bio-Trap® indicating that chemisorbed amendments are bioavailable. However, there was a clear effect of phenol concentration on 13C incorporation in both biomass and DIC confirming phenol inhibition. These results suggest that physical reductions of the phenol concentrations in some areas of the plume will be required before biodegradation of phenol can proceed at a reasonable rate. © 2013 Wiley Periodicals, Inc.Remediation Journal 12/2013; 23(1).
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ABSTRACT: In situ amendments are a promising approach to enhance removal of metal contaminants from diverse environments including soil, groundwater and sediments. Apatite and chitin were selected and tested for copper, chromium, and zinc metal removal in marine sediment samples. Microbiological, molecular biological and chemical analyses were applied to investigate the role of these amendments in metal immobilization processes. Both apatite and chitin promoted micro-bial growth. These amendments induced corresponding bacterial groups including sulfide producers, iron reducers, and phosphate solubilizers; all that facilitated heavy metal immobilization and removal from marine sediments. Molecular biological approaches showed chitin greatly induced microbial population shifts in sediments and overlying water: chi-tin only, or chitin with apatite induced growth of bacterial groups such as Acidobacteria, Betaproteobacteria, Epsilon-proteobacteria, Firmicutes, Planctomycetes, Rhodospirillaceae, Spirochaetes, and Verrucomicrobia; whereas these bacteria were not present in the control. Community structures were also altered under treatments with increase of rela-tive abundance of Deltaproteobacteria and decrease of Actinobacteria, Alphaproteobacteria, and Nitrospirae. Many of these groups of bacteria have been shown to be involved in metal reduction and immobilization. Chemical analysis of pore-and overlying water also demonstrated metal immobilization primarily under chitin treatments. X-Ray absorp-tion spectroscopy (XAS) spectra showed more sorbed Zn occurred over time in both apatite and chitin treatments (from 9% -27%). The amendments improved zinc immobilization in marine sediments that led to significant changes in the mineralogy: easily mobile Zn hydroxide phase was converted to an immobile Zn phosphate (hopeite). In-situ amendment of apatite and chitin offers a great bioremediation potential for marine sediments contaminated with heavy metals.Open Journal of Metal 07/2013; 3.
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ABSTRACT: Biofilms formed by dissimilatory metal reducers are of interest to develop permeable biobarriers for the immobilization of soluble contaminants such as uranium. Here we show that biofilms of the model uranium-reducing bacterium Geobacter sulfurreducens immobilized substantially more U(VI) than planktonic cells and for longer periods of time, reductively precipitating it to a mononuclear U(IV) phase involving carbon ligands. The biofilms also tolerated high and otherwise toxic concentrations (up to 5 mM) of uranium, consistent with a respiratory strategy that also protected the cells from uranium toxicity. The enhanced ability of the biofilms to immobilize uranium correlated only partially with the biofilm biomass and thickness and depended greatly on the area of the biofilm exposed to the soluble contaminant. By contrast, uranium reduction depended on the expression of Geobacter conductive pili and, to a lesser extent, to the presence of the c-cytochrome OmcZ in the biofilm matrix. The results support a model in which the electroactive biofilm matrix immobilizes and reduces the uranium in the top stratum. This mechanism prevents the permeation and mineralization of uranium in the cell envelope, thereby preserving essential cellular functions and enhancing the catalytic capacity of Geobacter cells to reduce uranium. Hence, the biofilms provide cells with a physical and chemical protective environment for the sustained immobilization and reduction of uranium that is of interest for the development of improved strategies for the in situ bioremediation of environments impacted by uranium contamination.Applied and Environmental Microbiology 08/2014; · 3.95 Impact Factor