231 research outputs found
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Resolving the Impact of Biological Processes on DNAPL Transport in Unsaturated Porous Media through Nuclear Magnetic Resonance Relaxation Time Measurements
This research leads to a better understanding of how physical and biological properties of porous media influence water and dense non-aqueous phase liquid (DNAPL) distribution under saturated and unsaturated conditions. This project exploits the capability of low-field nuclear magnetic resonance (NMR) proton relaxation decay-rate measurements for determining environmental properties affecting DNAPL solvent flow in the subsurface, including determining if DNAPL exist in water-wet or solvent-wet environments, the pore-size distribution of the soils containing DNAPLs, and the impact of biological processes on their transport mechanisms in porous media. Knowledge of the in-situ flow properties and pore distributions of organic contaminants are critical to understanding where and when these fluids will enter subsurface aquifers
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Microbially Promoted Solubilization of Steel Corrosion Products and Fate of Associated Actinides
The ultimate goal of this project was to demonstrate that metal-reducing bacteria could be used to remove heavy metal and radionuclide contaminants from the surfaces of corroding steel surfaces. Toward this end, fundamental scientific issues regarding (1) factors influencing the adhesion and colonization of DIB on mineral surfaces, (2) the enzymatic activity of cells once they have adhered to mineral surfaces, (3) and (4) methods for recovering bacteria and attendant radionuclides following release from mineral surfaces were addressed. The fate of radionuclides (plutonium) contaminants following reduction by DIRB
Persistent Transport Barrier on the West Florida Shelf
Analysis of drifter trajectories in the Gulf of Mexico has revealed the
existence of a region on the southern portion of the West Florida Shelf (WFS)
that is not visited by drifters that are released outside of the region. This
so-called ``forbidden zone'' (FZ) suggests the existence of a persistent
cross-shelf transport barrier on the southern portion of the WFS. In this
letter a year-long record of surface currents produced by a Hybrid-Coordinate
Ocean Model simulation of the WFS is used to identify Lagrangian coherent
structures (LCSs), which reveal the presence of a robust and persistent
cross-shelf transport barrier in approximately the same location as the
boundary of the FZ. The location of the cross-shelf transport barrier undergoes
a seasonal oscillation, being closer to the coast in the summer than in the
winter. A month-long record of surface currents inferred from high-frequency
(HF) radar measurements in a roughly 60 km 80 km region on the WFS off
Tampa Bay is also used to identify LCSs, which reveal the presence of robust
transient transport barriers. While the HF-radar-derived transport barriers
cannot be unambiguously linked to the boundary of the FZ, this analysis does
demonstrate the feasibility of monitoring transport barriers on the WFS using a
HF-radar-based measurement system. The implications of a persistent cross-shelf
transport barrier on the WFS for the development of harmful algal blooms on the
shoreward side of the barrier are considered.Comment: Submitted to Geophysical Research Letter
Interaction of desulfovibrio desulfuricans biofilms with stainless steel surface and its impact on bacterial metabolism
Aims: To study the influence of some metallic elements of stainless steel 304 (SS 304) on the development and activity of a sulfate-reducing bacterial biofilm, using as comparison a reference nonmetallic material polymethylmethacrylate (PMMA).
Methods and Results: Desulfovibrio desulfuricans biofilms were developed on SS
304 and on a reference nonmetallic material, PMMA, in a flow cell system.
Steady-state biofilms were metabolically more active on SS 304 than on PMMA. Activity tests with bacteria from both biofilms at steady state also showed that the doubling time was lower for bacteria from SS 304 biofilms.
The influence of chromium and nickel, elements of SS 304 composition, was
also tested on a cellular suspension of Des. desulfuricans. Nickel decreased the bacterial doubling time, while chromium had no significant effect.
Conclusions: The following mechanism is hypothesized: a Des. desulfuricans
biofilm grown on a SS 304 surface in anaerobic conditions leads to the weakening
of the metal passive layer and to the dissolution in the bulk phase of nickel ions that have a positive influence on the sulfate-reducing bacteria metabolism.
This phenomenon may enhance the biocorrosion process.
Significance and Impact of the Study: A better understanding of the interactions between metallic surfaces such as stainless steel and bacteria commonly implied in the corrosion phenomena which is primordial to fight biocorrosion.Programme Praxis XXI; University of Santiago de
Compostela
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Substrate capture by a psychrophilic marine bacterium
Cells of the marine bacterium, Ant-300, accumulate loosely bound
amino acids during amino acid uptake. The fraction of amino acid taken
up that exists in the loosely bound state depends on the substrate in
question. Shock treatment studies indicate that, in general, the initial binding, uptake, and retention of amino acids are sensitive to reduced
osmolarity and salt concentration. Cellular components that bind
the amino acids arginine and lysine are released from the cells during
shock treatment. Charge interactions appear to be responsible for the
reversible formation of the ligand-protein complex. It is proposed that
these components, presumably proteins, mediate the capture of the amino
acids arginine and lysine at the surface of the cell. Chemotaxis provides
the cell the opportunity to migrate from areas of low arginine
concentration to areas of high arginine concentration. Arginine transport
into the cell is mediated by two high affinity components with kinetic
constants of 1.2 x 10⁻⁸ and 4.5 x 10⁻⁷M. These mechanisms enable
Ant-300 to scavenge nutrients in the marine environment, thereby assuring
its own survival and promoting the regeneration of nutrients
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Some physiological effects of near maximum growth temperatures on an obligately psychrophilic marine bacterium
The heat inactivation of the psychrophilic marine bacterium,
Ant-300, was investigated in terms of permeability control, glucose
uptake, and respiration. Extensive leakage of 14C-cellular material
occurred at 13 C, the maximum growth temperature of the organism.
Protein and RNA were released from the cells in significant
quantities. Inhibition of glucose uptake also occurred at 13 C
when the cells were suspended in artificial seawater. Higher
temperatures increased both the rate and extent of inhibition.
The presence of nutrients in the cell menstruum afforded some protection to the uptake mechanism against heat injury. In addition,
nutrients increased cell viability above the maximum growth temperature.
CO₂ evolution at and slightly above the maximum growth
temperature appeared to be inhibited more by a limited supply of
glucose as substrate than by direct heat damage to the respiratory
system. Starvation, resulting from extensive leakage of intracellular
material as well as inhibited substrate uptake, was suggested as a cause for the organism's inability to grow at temperatures
above 13 C
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