BER Research Highlights

Search Date: April 29, 2017

11 Records match the search term(s):


November 25, 2015

Uranium Accumulated in Anoxic Sediments Threatens Groundwater Quality at Contaminated Department of Energy Sites

Anoxic, organic-rich sediments in the subsurface retain enough uranium to sustain a groundwater plume for centuries.

The Science  
Sediment cores sampled at “high resolution” for the first time (~10-cm depth intervals) from wells on a uranium contaminated floodplain near Rifle, Colorado, revealed that uranium has accumulated exclusively within organic-enriched sulfidic sediments. Molecular investigations of uranium and sulfur at this Department of Energy site indicated that uranium was present in a non-crystalline reduced (tetravalent) form and that even the interior parts of these sediment bodies are oxidized on an annual basis.

The Impact
Release of uranium from anoxic, organic-enriched sediment bodies, defined through these detailed, centimeter-scaled investigations, could sustain a contaminant groundwater plume for centuries. Similar types of sulfidic, organic-enriched sediment bodies exist in other uranium contaminated aquifers in the upper Colorado River Basin, meaning that these findings could offer regionally important explanations to uranium behavior. These new results highlight the need for better understanding of the vulnerability of anoxic, organic-rich sediments in this region to climate perturbations.

Summary
Uranium mobility is regulated by its chemical state; the reduced form, U(IV), is much less soluble than the oxidized U(VI). Consequently, oxidation of anoxic sediments could allow uranium to enter the aquifer at the Rifle site with a long-term impact on groundwater quality. The co-occurrence of uranium, sulfur, and organic carbon in the Rifle subsurface suggests that sulfate reduction coupled to microbial carbon oxidation is an important regulator of uranium retention in this floodplain. Sulfur was only found to accumulate in groundwater saturated fine-grained materials with an elevated organic carbon content, supporting the conclusion that reducing conditions, induced by the low permeability and microbial oxygen consumption, promote sulfide formation and uranium retention. The co-existence of multiple sulfur species (sulfate, elemental sulfur, mackinawite, greigite, and pyrite) throughout the reduced zone, suggests redox cycling of these materials, which implies oxidative release of uranium occurs. Uranium was found to be associated with both organic carbon and sulfur, respectively. Therefore, the study concluded that uranium reduction and retention in these sediments resulted from abiotic reduction by iron sulfides, potentially enhanced by organic matter shuttling electrons, as well as via biotic reduction through respiratory and enzymatic activity coupled to organic matter decomposition.

Contacts (BER PM)
Roland F. Hirsch, SC-23.2, roland.hirsch@science.doe.gov, 301-903-9009

(PI Contact)
John Bargar
Stanford Synchrotron Radiation Lightsource
SLAC National Accelerator Laboratory
bargar@slac.stanford.edu

Funding
This work was supported as part of the SLAC Scientific Focus Area (SFA), which is funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Subsurface Biogeochemical Research (SBR) program under subcontract DE-AC02-76SF00515. Logistical support was provided by the Rifle field research program of the Lawrence Berkeley National Laboratory, through SBR funding to the Sustainable Systems SFA under contract DE-AC02-05CH11231. Portions of the work were performed at the Stanford Synchrotron Radiation Lightsource at the SLAC National Accelerator Laboratory.

Publication
Janot, N.,et al. 2016. “Physico-Chemical Heterogeneity of Organic-Rich Sediments in the Rifle Aquifer, CO: Impact on Uranium Biogeochemistry,” Environmental Science and Technology 50(1), 46-53. DOI: 10.1021/acs.est.5b03208. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 17, 2015

Calcium and Phosphate Can Affect How Uranium Contamination Travels Through the Environment

The molecular form and the oxidation of subsurface uranium are affected by common groundwater constituents.

The Science  
Calcium and phosphate are environmental components found in animal bone, various minerals, and groundwater. A recent study has demonstrated that these ions slow down the oxidation of subsurface-relevant uranium species and change the oxidized form of uranium into a more stable mineral.

The Impact
The effect of environmental factors like calcium and phosphate on transformations of some newly discovered forms of uranium found in groundwater are currently unknown. This study determined uranium valence and molecular structure using state-of-the-art spectroscopy techniques to provide information necessary for accurately predicting uranium transport.

Summary
The mobility of uranium in subsurface environments depends strongly on its oxidation state, with chemically reduced UIV phases being significantly less soluble than UIV minerals. A team of scientists from Argonne National Laboratory, Illinois Institute of Technology, and Bulgarian Academy of Sciences compared the oxidation kinetics and mechanisms of two potential products of UIV reduction in natural systems: a nanoparticulate UO2 phase and an amorphous UIV-Ca-PO4 phase. The valence and molecular structure of uranium was tracked by synchrotron x-ray absorption spectroscopy. Similar oxidation rates for the two phases were observed in solutions equilibrated with atmospheric O2 and CO2. Addition of up to 400 µM Ca and PO4 decreased the oxidation rate by an order of magnitude for both UO2 and UIV-phosphate. In the absence of Ca or PO4, the product of UO2 oxidation was Na-uranyl oxyhydroxide, whereas the product of UIV-Ca-PO4 oxidation was a UIV-phosphate phase (autunite). In the presence of Ca or PO4, the oxidation proceeded to UIV-phosphate for both pre-oxidation forms of UIV. Addition of Ca or PO4 changed the mechanism of oxidation by causing the formation of a passivation layer on the particle surfaces.

Contacts (BER PM)
Roland F. Hirsch, roland.hirsch@science.doe.gov, 301-903-9009

(PI Contact)
Kenneth M. Kemner
Argonne National Laboratory
kemner@anl.gov, 630-252-1163

Funding
This research is part of the Subsurface Science Scientific Focus Area at Argonne National Laboratory (ANL), which is supported by the U.S. Department of Energy’s (DOE) Subsurface Biogeochemical Research Program, Office of Biological and Environmental Research, Office of Science. Use of the Electron Microscopy Center and Advanced Photon Source at ANL is supported by DOE’s Office of Science, Office of Basic Energy Sciences. MRCAT/EnviroCAT operations are supported by DOE and the MRCAT/EnviroCAT member institutions. All work at ANL was under Contract DE-AC02-06CH11357.

Publications
Latta, D. E., K. M. Kemner, B. Mishra, and M. I. Boyanov. 2016. “Effects of Calcium and Phosphate on Uranium(IV) Oxidation: Comparison Between Nanoparticulate Uraninite and Amorphous UIV–Phosphate,” Geochimica et Cosmochimica Acta 174, 122–42. DOI: 10.1016/j.gca.2015.11.010. (Reference link)  

Related Links
Subsurface Science Scientific Focus Area at Argonne National Laboratory.

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 09, 2015

Global Prevalence and Distribution of Genes and Microbes involved in Mercury Methylation

It is well known that the methylation of mercury (Hg) is mediated by bacteria and produces neurotoxic methylmercury (MeHg), which is also highly bioaccumulative in living organisms. However, the specific environments or locations in which MeHg is created are not well understood or identified. The recent finding of the specific genes (hgcAB) involved in Hg methylation provides a potential tool for scientists to identify the specific environments or locations where MeHg is created. Because the hgcAB genes are highly conserved, a team of scientists from Oak Ridge National Laboratory, Smithsonian Environmental Research Center, and Texas A&M University realized that they had a foundation for broadly evaluating spatial and niche-specific patterns of microbial Hg-methylation potential in natural environments. The team primarily used assembled and annotated data publicly available from the Department of Energy’s Joint Genome Institute to query hgcAB diversity and distribution in >3,500 publically available microbial metagenomes, encompassing a broad range of global environments. The hgcAB genes were found in nearly all anaerobic, but not aerobic, environments including oxygenated layers of the open ocean. Critically, hgcAB was effectively absent in ~1500 human and mammalian microbiomes, suggesting a low risk of endogenous MeHg production. New potential methylation habitats were identified, including invertebrate digestive tracts, thawing permafrost, coastal “dead zones,” soils, sediments, and extreme environments, suggesting multiple routes for MeHg entry into food webs. Several new taxonomic groups capable of Hg methylation emerged, including lineages having no cultured representatives. Phylogenetic analysis points to an evolutionary relationship between hgcA and genes encoding the corrinoid iron-sulfur proteins functioning in the ancient Wood-Ljungdahl carbon fixation pathway, suggesting that methanogenic archaea may have been the first to perform these biotransformations.

References: Podar, M., C. C. Gilmour, C. C. Brandt, A. Soren, S. D. Brown, B. R. Crable, A. V. Palumbo, A. C. Somenahally, and D. A. Elias. 2015. “Global Prevalence and Distribution of Genes and Microorganisms involved in Mercury-Methylation,” Science Advances 1(9), e1500675.  DOI: 10.1126/sciadv.1500675. (Reference link)
See also ORNL News Release.

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 08, 2015

Detecting Technetium in Groundwater

Novel approach uses salt-based sensor.

The Science
Technetium-99 (99Tc) is a long-lived radionuclide byproduct of the nuclear fuel cycle, making it a major risk driver at former nuclear weapons production sites that requires onsite monitoring. A novel approach has been demonstrated that uses highly selective and sensitive platinum salt to detect and quantify the highly soluble pertechnetate (TcO4-) anion in groundwater.

The Impact
The new anion recognition approach has potential for the development of a field-deployable and highly accurate sensor for monitoring TcO4- in groundwater, river water, and watersheds. This work could have a broad impact on remediation efforts, paving the way for the development of similar salts for detection of other important environmental contaminants.

Summary
When exposed to moderately oxidizing conditions, 99Tc is readily converted to pertechnetate (TcO4-), a highly soluble anion that can migrate into groundwater and the environment. Existing methods for onsite monitoring of TcO4- in groundwater require a complicated series of analytical steps due to the low selectivity and sensitivity of Tc. A team of scientists from Pacific Northwest National Laboratory (PNNL), Environmental Molecular Sciences Laboratory [EMSL; a U.S. Department of Energy (DOE) user facility], University of Cincinnati, and Florida State University searched for a suitable material for sensing TcO4- in water. The team evaluated simple salts of transition metal complexes that change in color and luminescence properties upon exposure to the Tc anion using the SPEX Fluorolog 2 fluorimeter at EMSL. They found one specific platinum salt that undergoes a dramatic color and brightness change upon exposure to TcO4-; the salt was highly sensitive and enables detection of TcO4- at levels well below the drinking water standard established by the U.S. Environmental Protection Agency. Modeling and simulation work using EMSL’s Cascade supercomputer enabled the team to determine that the high selectivity was due to the unique electronic structure of the platinum salt. Unlike currently available methods for TcO4- sensing, the new approach does not require separation, concentration, or other pretreatment steps. Thus, the rapid, sensitive, and accurate TcO4- sensing system is ideal for real-time deployment at contaminated sites. Future implementation of this type of ion recognition system has great potential for remediation efforts and could be essential in addressing a broad range of environmental and health concerns.

BER PM Contact:
Paul Bayer, SC-23.1, 301-903-5324

PI Contacts:
Sayandev Chatterjee
PNNL
sayandev.chatterjee@pnnl.gov

Tatiana Levitskaia
PNNL
tatiana.levistkaia@pnnl.gov

Funding
This work was supported by DOE’s Office of Science, Office of Biological and Environmental Research and Office of Basic Energy Sciences, including support of EMSL; PNNL’s Laboratory-Directed Research and Development Program; National Science Foundation; and Office of Environmental Management Sciences Program.

Publications
Chatterjee, S., A. E. Norton, M. K. Edwards, J. M. Peterson, S. D. Taylor, S. A. Bryan, A. Andersen, N. Govind, T. E. Albrecht-Schmitt, W. B. Connick, and T. G. Levitskaia. 2015. “Highly Selective Colorimetric and Luminescence Response of a Square-Planar Platinum(II) Terpyridyl Complex to Aqueous TcO4–,” Inorganic Chemistry 54(20), 9914–23. DOI:   10.1021/acs.inorgchem.5b01664. (Reference link)

Related Links
EMSL article

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 02, 2015

Potential for Reoxidation of Iron-Chromium Precipitates by Manganese Oxide

Reductive immobilization of hexavalent chromium (Cr(VI)), often forming Fe-Cr precipitates, is a frequent remediation alternative, yet the relationship between the conditions of precipitate formation, the structural and chemical properties of the precipitates, and the rate and extent of precipitate oxidation by Mn oxides is needed. This study provided a systematic investigation of the rates of Cr(VI) reduction by both abiotic minerals and a chromium reducing bacterium, the properties of the resulting Fe-Cr precipitates, and the susceptibility for reoxidation and remobilization of Cr(VI) upon precipitate exposure to the manganese oxide birnessite.

The properties of the resulting Fe-Cr solids and their behavior upon exposure to birnessite differed significantly. In microcosms where Cr(VI) was reduced by Desulfovibrio vulgaris strain RCH1, and where hematite or Al-goethite were present as iron sources, there was significant initial loss of Cr(VI) in a pattern consistent with adsorption, and significant Cr(VI) was found in the resulting solids. The solid formed when Cr(VI) was reduced by FeS contained a high proportion of Cr(III) and was poorly crystalline. Reaction between birnessite and the abiotically formed Cr(III) solids led to production of significant dissolved Cr(VI) compared to the no-birnessite controls. This pattern was not observed in the solids generated by microbial Cr(VI) reduction, and could be due to re-reduction of any Cr(VI) generated upon oxidation by birnessite via active bacteria or microbial enzymes.

The results of this study suggest that Fe-Cr precipitates formed in groundwater remediation may remain stable only in the presence of active anaerobic microbial reduction. If exposed to environmentally common Mn oxides such as birnessite in the absence of microbial activity, there is the potential for rapid (re)formation of dissolved Cr(VI) above regulatory levels.

Citation:
Butler, E. C., Chen, L., Hansel, C. M., Krumholz, L. R., Elwood Madden, A. S., Lan, Y. (2015), Biological versus mineralogical chromium reduction: Potential for reoxidation by manganese oxide, Environ. Sci.: Processes Impacts 17, 1930-1940, DOI: 10.1039/C5EM00286A.

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Abiotic reduction of Cr(VI) by FeS and reduced nontronite led to precipitates that released significant Cr(VI) when exposed to birnessite. Figure reproduced from Environ. Sci.: Processes Impacts 17 (2016), 1930–1940 (DOI: 10.1039/C5EM00286A) with permission from the Royal Society of Chemistry.



September 27, 2015

Colloid Deposit Morphology Controls Permeability in Porous Media

Processes occurring in soils and aquifers play a crucial role in contaminant remediation and carbon cycling. The flow of water through porous media like soils and aquifers is essential for contaminant remediation and carbon cycling and depends on the permeability, which determines how much water flows for a given hydraulic driving force. Widely recognized is that colloids (fine particles including soils, chemical precipitates, and bacteria) often control permeability and that colloid deposit morphology (the structure of deposited colloids) is a fundamental aspect of permeability. Until recently, however, no experimental techniques were available to measure colloid deposit morphology within porous media. A recent study, led by the University of Colorado Denver in collaboration with Lawrence Berkeley National Laboratory, used a custom-designed experimental apparatus to perform a series of experiments using static light scattering (SLS) to characterize colloid deposit morphology within refractive index matched (RIM) porous media during flow through a column. Real-time measurements of permeability, specific deposit, and deposit morphology were conducted with initially clean porous media at various ionic strengths and water velocities. Decreased permeability (i.e., increased clogging) correlated with colloid deposit morphology, specifically with lower fractal dimension and smaller radius of gyration. These observations suggest a deposition scenario in which large and uniform aggregates become deposits, reducing porosity, and lead to higher fluid shear forces, which then decompose the deposits, filling the pore space with small and dendritic fragments of aggregate. Accordingly, for the first time, observations are available to quantify the relationship between the macroscopic variables of ionic strength and water velocity and the pore-scale variables of colloid deposit morphology, which can be conceptualized as an emergent property of the system. This research paves the way for future studies to quantify the complex feedback process between flow, chemistry, and biology in soils and aquifers.

Reference: Roth, E. J., B. Gilbert, and D. C. Mays. 2015. “Colloid Deposit Morphology and Clogging in Porous Media: Fundamental Insights Through Investigation of Deposit Fractal Dimension,” Environmental Science and Technology 49(20), 12263–70. DOI: 10.1021/acs.est.5b03212. (Reference link)

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Permeability, which is crucial in groundwater remediation, depends on colloidal deposit morphology. A novel application of static light scattering has enabled first-of-their-kind, real-time, in situ measurements of deposit morphology as a fractal dimension during column filtration experiments. [Image courtesy Roth, Gilbert, and Mays 2015]



June 19, 2015

New Molecular Insights into the Structural Mechanism of Uraninite Oxidation

Molecular-scale information reveals non-classical diffusion behavior during the initial stages of uranium dioxide corrosion.

The Science
Density-functional theory and X-ray based methods sensitive to surface atomic structure and oxidation state [crystal truncation rod (CTR), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS)] were used to determine the behavior of the natural cleavage surface of uraninite (UO2) in water at ambient conditions. Oxygen was found to react strongly with UO2. However, rather than following classical diffusion patterns, oxygen self-organized as interstitial atoms within the mineral lattice of every third atomic layer.

The Impact
Uranium dioxide occurs naturally in anoxic sediments, is the desired product of in situ bioremediation of uranium-contaminated aquifers, and is likely to control uranium release from such sediments over the long term. These surprising insights indicate that UO2 oxidation is far more complicated that previously known and offer a new conceptual molecular-scale framework for understanding UO2 fate in the environment.  

Summary
CTR X-ray diffraction measurements of a polished UO2 (111) surface exposed to atmospheric oxygen revealed a periodic, oscillatory structure of the oxidation front perpendicular to the mineral-water interface. This behavior could be explained by quantum mechanic considerations of the electron-transfer from U 5f orbitals to O 2p orbitals, assuming at least partial contribution from hemi-uranyl (resembling half of the UO22+ uranyl cation, i.e., with only a single short U-O bond) termination groups at the mineral surface, which favor the incorporation of interstitial oxygens into slab 3 of the UO2 lattice. The presence of hemi-uranyl termination groups was supported by XPS analyses revealing that both U(V) and U(VI) were present at the mineral surface, suggesting a mixed termination of the oxidized surface with hemi-uranyl, hydroxyl, and molecular water. The ordered oscillatory oxidation front with a three-layer periodicity observed is distinct from previously proposed models of oxidative corrosion under vacuum and offers important molecular-scale insights into UO2 oxidation under ambient conditions.

Contact (BER PM)
Roland F. Hirsch, SC-23.2, roland.hirsch@science.doe.gov, 301-903-9009

(PI Contact)
John Bargar
SSRL, SLAC National Accelerator Laboratory
bargar@slac.stanford.edu

Funding
Support was provided by the U.S. Department of Energy (DOE), Office of Science, Biological and Environmental Research (BER), Subsurface Biogeochemical Research activity, through the SLAC Scientific Focus Area program (Contract No. DE-AC02-76SF00515); and by the Geosciences Research Program at Pacific Northwest National Laboratory (PNNL), funded by DOE’s Office of Basic Energy Sciences (BES). XPS data were collected in the Radiochemistry Annex at the Environmental Molecular Sciences Laboratory, a DOE user facility located at PNNL. A portion of the DFT study was also performed using the computational resources of EMSL. GeoSoilEnviroCARS is supported by the National Science Foundation-Earth Sciences (EAR-1128799) and BES GeoSciences (DE-FG02-94ER14466). This research used resources at the Advanced Photon Source, a DOE user facility.

Publication
Stubbs, J. E.,et al. 2015. “UO2 Oxidative Corrosion by Nonclassical Diffusion,” Physical Review Letters 114, 246103. DOI: 10.1103/PhysRevLett.114.246103. (Reference link)

Related Links
ANL Highlight

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 12, 2015

Using Natural Microbial Communities as Biosensors for Environmental Contaminants

Microbial communities are highly attuned to changes in environmental conditions, rapidly sensing and responding to shifts in temperature, pH, nutrient availability, toxin levels, and dozens of other variables. For decades, scientists have studied the abilities of microbes to survive exposure to (and in some cases make use of) environmental contaminants such as heavy metals, radionuclides, and hydrocarbons. However, microbial communities can contain hundreds of different species, and this complexity makes it extremely difficult to quantitatively measure community-level responses to contaminant exposure. In a new study, a team of researchers from Lawrence Berkeley National Laboratory’s ENIGMA (Ecosystems and Networks Integrated with Genes and Molecular Assemblies) science focus area developed a new computational approach for the analysis and computational modeling of microbial community responses to environmental contaminants. Using direct sequencing of DNA from environmental samples, the team examined the microbial community of a subsurface aquifer in Oak Ridge, Tennessee, that had been contaminated with uranium, nitrate, and a variety of other compounds. Drawing on this data, a modeling framework was constructed to enable prediction of the types and amounts of contaminants that had been experienced by the microbial community based on known physiological characteristics of detected bacterial species. The predictions of this model strongly correlated with amounts of uranium, nitrate, and a variety of other geochemical factors measured at the sampling sites. To test the utility of this approach using an independent dataset, the team applied the model to microbial DNA samples collected during the Deepwater Horizon oil spill in 2010. Again, the model accurately predicted which samples had experienced oil contamination based on microbial DNA sequences and suggested that the community fingerprint retained a “memory” of exposure even after oil was no longer detectable. The results of this study provide a powerful new approach for not only the identification of contaminants in environmental samples, but also the microbial processes that are acting on them and potentially impacting their movement and/or longevity in the environment.

Reference: Smith, M. B., A. M. Rocha, C. S. Smillie, S. W. Oleson, C. J. Paradis, L. Wu, J. H. Campbell, J. L. Fortney, T. L. Mehlhorn, K. A. Lowe, J. E. Earles, J. Phillips, S. M. Techtmann, D. C. Joyner, S. P. Preheim, M. S. Sanders, J. Yang, M. A. Mueller, S. C. Brooks, D. B. Watson, P. Zhang, Z. He, E. A. Dubinsky, P. D. Adams, A. P. Arkin, M. W. Fields, J. Zhou, E. J. Alm, and T. C. Hazen. 2015. “Natural Bacterial Communities as Quantitative Biosensors,” mBio 6(3), e00326-15. DOI: 10.1128/mBio.00326-15. (Reference link)

Contact: Joseph Graber, SC-23.2, (301) 903-1239
Topic Areas:

Division: SC-23.2 Biological Systems Science Division, BER


March 27, 2015

Microbes Use Tiny Magnets as Batteries

Understanding subsurface electron flow is vital in understanding elemental cycling and remediating subsurface pollutants, including those from recent energy technologies and historic waste sites. Research into the flow of electrons can show how certain minerals and bacteria work together via reduction-oxidation reactions to shape the geochemical landscape at Earth’s near surface and possibly halt toxins from spreading. The scientific challenge is how to unravel complex communities of organisms and mineral assemblages in nature into key cooperative subsystems that can be studied in the laboratory to determine how they work. In a recent study, scientists at the University of Tuebingen, University of Manchester, and Pacific Northwest National Laboratory discovered that during the day, one species of bacteria withdraws electrons from the iron-based mineral magnetite. At night, another species adds electrons back to the mineral, where the electrons reside until the daytime bacteria are active. The phototrophic Fe(II)-oxidizing Rhodopseudomonas palustris TIE-1 and the anaerobic Fe(III)-reducing Geobacter sulfurreducens work together to use magnetite's iron ions as both electron sources and sinks under different day and night conditions. The researchers used a host of instruments to make this discovery, including transmission electron microscopy resources at the Department of Energy’s Environmental Molecular Sciences Laboratory. The research shows that the common iron oxide mineral magnetite can serve as a naturally occurring battery for two very different types of bacteria that depend on iron to survive, revealing that a single mineral can serve as a platform for microbial diversity in nature.

Reference: Byrne, J. M., N. Klueglein, C. Pearce, K. M. Rosso, E. Appel, and A. Kappler. 2015. “Redox Cycling of Fe(II) and Fe(III) in Magnetite by Fe-Metabolizing Bacteria,” Science 347(6229),1473–76. DOI: 10.1126/science.aaa4834. (Reference link)

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



In the subsurface environment, below the water level, iron-oxidizing bacteria strip electrons from the naturally occurring battery (left); the reducing bacteria, which are active at night, add electrons, effectively recharging the battery (right). [Image courtesy University of Tuebingen]



March 03, 2015

Immobilization of Heavy Metals via Two Parallel Pathways During In Situ Bioremediation

Bioreduction is being actively investigated as an effective strategy for subsurface remediation and long-term management of Department of Energy (DOE) sites contaminated by metals and radionuclides [i.e., uranium (VI)]. These strategies require manipulation of the subsurface, usually through injection of chemicals (e.g., electron donor), which mix at varying scales with the contaminant to stimulate metal-reducing bacteria. Evidence from DOE field experiments suggests that mixing limitations of substrates at all scales may affect biological growth and activity for U(VI) reduction.

To study the effects of mixing on U(VI) reduction, researchers used selenite, Se(IV), instead of U(VI) in the lab because Se(IV) is easier to handle and microbial reduction of Se(IV) and U(VI) is similar in that two immobilization pathways are involved. In one pathway, the soluble contaminant [Se(IV) or U(VI)] is biologically reduced to a solid [Se0 or U(IV)]. In the other pathway, sulfate, which is commonly present in groundwater, is first biologically reduced to sulfide; this product then abiotically reacts with the soluble contaminant [Se(IV) or U(VI)] to form a solid [selenium sulfide or U(IV)]. While the first pathway is well understood, the second pathway has not been widely studied. Another unique aspect of this study is that researchers investigated mixing and reaction in a microfluidic flow cell with realistic pore geometry and flow conditions that mimic the transverse-mixing dominated reaction zone along the margins of a selenite plume undergoing bioremediation due to injected electron donors in the presence of background sulfate. Microbial and chemical reaction products were characterized using advanced microscopic and spectroscopic methods. A continuum-scale reactive transport model also was developed to simulate this experiment.

Results demonstrate that engineering remediation of metal-contaminated sites via electron-donor addition can lead to secondary and abiotic reactions that can immobilize metals, in addition to previously studied biotic reactions. The improved understanding of selenite immobilization as well as the improved model can help in the design of in situ bioremediation processes for groundwater contaminated by selenite or other contaminants [e.g., U(IV)] that can be immobilized via similar pathways.

Reference: Tang, Y., C. J. Werth, R. A. Sanford, R. Singh, K. Michelson, M. Nobu, W. Liu, and A.J. Valocchi. 2015. “Immobilization of Selenite via Two Parallel Pathways During In Situ Bioremediation,” Environmental Science and Technology 49, 4543–50. DOI: 10.1021/es506107r. (Reference link)

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 15, 2015

Newly Identified Archaea Involved in Anaerobic Carbon Cycling

Archaea, a domain of single-celled microorganisms, represent a significant fraction of Earth’s biodiversity, yet much less is known about Archaea than bacteria. One reason for this lack of knowledge is relatively poor genome sampling, which has limited accuracy for the Archaeal phylogenetic tree. To obtain a better understanding of the diversity and physiological functions of members of the Archaea domain, a team of scientists from the University of California, Berkeley, The Ohio State University, Columbia University, Lawrence Berkeley National Laboratory, the Department of Energy’s (DOE) Joint Genome Institute, Pacific Northwest National Laboratory, and DOE Environmental Molecular Sciences Laboratory used genome-resolved metagenomics analyses to investigate the diversity, genome sizes, metabolic capabilities, and potential environmental niches of Archaea from the Rifle, Colorado, uranium mill tailings site. The team used DOE JGI to sequence DNA from Rifle sediment and groundwater samples, and they not only identified new sequences for more than 150 Archaea but were able to reconstruct the complete genomes of two Archaea that were demonstrated to be representative of two different phyla. Transcriptomic studies conducted using EMSL capabilities on one of these microbes demonstrate that they have small genomes and limited metabolic capabilities; however, these metabolic capabilities are associated with carbon and hydrogen metabolism. These results suggest that these Archaea are either symbionts or parasites that depend on other organisms for some of their metabolic requirements. This research approximately doubled the known genomic diversity of Archaea, reconstructed the first complete genomes for Archaea using cultivation-independent methods, and enabled an extensive revision of the Archaeal tree of life. In addition, these findings can be incorporated into genome-resolved ecosystem models to more accurately reflect the role played by Archaea in the global carbon cycle.

References: Castelle, C. J., K. C. Wrighton, B. C. Thomas, L. A. Hug, C. T. Brown, M. J. Wilkins, K. R. Frischkorn, S. G. Tringe, A. Singh, L. M. Markillie, R. C. Taylor, K. H. Williams, and J. F. Banfield. “Genomic Expansion of Domain Archaea Highlights Roles for Organisms from New Phyla in Anaerobic Carbon Cycling,” Current Biology 25(6), 690-701. DOI: 10.1016/j.cub.2015.01.014. (Reference link)
(See also)

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324, Dan Drell, SC-23.2, (301) 903-4742, David Lesmes, SC 23.1, (301) 903-2977, Pablo Rabinowicz, SC-23.2 (301) 903-0379
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER,SC-23.2 Biological Systems Science Division, BER