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Undergraduate Research Opportunities Program

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Now showing 1 - 10 of 19

Lateral gene transfer of pandemic Vibrio parahaemolyticus genomic island genes

(Georgia Institute of Technology, 2008-12-15) Silberger, Daniel James

Vibrio parahaemolyticus is an emerging enteric pathogen. The O3:K6 serotype has become pandemic, and the genome has been sequenced for the RIMD2210633 strain of this serotype (20). The thermostabile direct hemolysin (tdh), thermostabile related hemolysin (trh), and two distinct Type III Secretion Systems (T3SS) have been implicated in virulence. Deletion studies have determined that the T3SS alone are sufficient to induce eukaryotic cell apoptosis. The T3SS loci are found within two separate genomic islands. Because genomic islands are known to be disseminated by Lateral Gene Transfer (LGT), we examined the distribution of the pandemic genomic island genes among clinical and environmental V. parahaemolyticus isolates and also among closely-related environmental Vibrio spp. using primers designed to amplify hemolysins and T3SS effectors previously characterized for V. parahaemolyticus strain RIMD2210633 (23). We also examined the distribution of a hypothetical bacteriocin, encoded by vpa1263, within another genomic island that is similar to the bacteriocins produced by Escherichia coli. Preliminary screens for the bacteriocin gene suggest that many clinical strains and some environmental strains contain vpa1263. PCR screens for the T3SS effector genes have shown that 22% of closely-related environmental Vibrio spp. contain at least one T3SS1 or one T3SS2 effector gene. Sequencing of housekeeping genes is ongoing to confirm these findings.
Density-dependent Stiffness in Petiole Biomechanics

(Georgia Institute of Technology, 2008-05-05) Wilson, Christina

Morphological features of plants vary with increasing size. This relationship between different physical characteristics and size is referred to as allometry. Recently allometric research focused on plants and in particular plant leaves due to their importance in nutrient flow and gas exchange. Allometric plant research aims to enhance our understanding of the ontogeny of plants and offers a tool for ecological modeling. Previous allometric models have glanced over the influence of biomechanics on leaf form and function. This research will test if density-dependent stiffness of petioles is variable or if it scales with leaf mass. In order to test the variance of stiffness in leaf petioles, Young s modulus (E) was measured by modeling the petioles as simply loaded beams. Young s modulus was shown to vary among different species, even those of the same genus. Density-dependent stiffness varied with leaf size for some herbaceous species but not for other woody tree species. Future research should investigate the biomechanical role of a possible redistribution of structural tissue and how this rearrangement would affects petiole stiffness and overall petiole function.
Repeated Testing of Working Memory Capacity

(Georgia Institute of Technology, 2008-05-05) Carter, Laura

Working memory capacity is measured by a variety of memory span tasks and can account for about 40% of inter-individual variation in fluid intelligence (Broadway &Engle, in preparation). In the present study, ten participants performed a widely accepted valid test of WMC, the Running Memory Span task (Pollack, Johnson, &Knaff, 1959), twenty-five times over five sessions to assess test-retest reliability and the extent of practice effects. Results confirmed expectations that memory performance would improve but that the rank ordering of individuals on performance would remain consistent over repeated testing.
Visual and Auditory Velocity Perception and Multimodal Illusions

(Georgia Institute of Technology, 2008-05-05) Gasaway, Katherine S.

Although ambiguous and conflicting sensory information from different sensory modalities is common, people seldom experience perceptual ambiguities or conflict between senses. Just as the retinal nerve blind spot is filled in and seldom seen, conflicting or otherwise confusing sensory information is resolved in favor of the most appropriate modality, eliminating the confusion from conscious experience. The ventriloquism effect and auditory driving are two examples of perceptual phenomena arising from this sensory override. This research explores the hypothesis that velocity perception is subject to the same effects. Subjects were presented with two bimodal (auditory-visual) stimulus pairs and asked to determine which of the visual stimuli was moving faster. In a V2A2/V2A1 condition, participants responded significantly more frequently that the first visual stimulus was faster than in any non-target condition. This effect was not found for V2A2/V2A3 trials.
Rotifer Ecotoxicology: Behavioral Avoidance of Toxicants

(Georgia Institute of Technology, 2008-05-05) Weigel, Emily G.

Previous rotifer ecotoxicology studies have shown varied effects of sublethal concentrations of hormones and metals on species but have largely ignored toxicant effects on behavior. Given the importance of chemical cues for mating, grazing, and predator avoidance, the phenomenon of behavioral response to pollutants is a critical topic impacting rotifer survival and reproduction. Dual- and tri-chamber test slides similar to Y-tubes were developed to test rotifer behavioral responses to sublethal concentrations of several toxicants. Rotifers were placed in a start chamber between a control chamber and test chamber containing a toxicant, and after fifteen minutes, rotifer distribution in all chambers was recorded. No significant distributional effects were observed for cadmium (2μg/L), pentochlorophenol (2μg/L), flutamide (8μg/L) nor progesterone (8μg/L). Significant deviation from a random distribution was recorded for selenium (2μg/L), lead (8μg/L), and rotifer conditioned medium. In addition, significant avoidance was found for copper (2μg/L) and mercury (0.2μg/L), even in tests with the start chamber containing the toxicant. These data suggest that rotifers can detect and avoid certain toxicants at sublethal levels. Avoidance often occurs at levels below published lethal concentrations (LC50s) on which many water quality criteria are based. Avoidance can alter rotifer survival and reproduction, leading to reductions in rotifer abundance and energy transfer to higher trophic levels.
Separation and Identification of Peptides by Supercritical Fluid Chromatography Coupled with Mass Spectrometry

(Georgia Institute of Technology, 2008-05-05) Terrett, Stuart

The presence of certain proteins in physiological fluids could be used as an early diagnostic tool for disease; however, because of the large concentration range of proteins and the number of distinct chemical species the detection and quantification of these proteins is problematic. This research focuses on the ability to separate proteins using supercritical fluid chromatography (SFC), a form of chromatography that uses supercritical carbon dioxide (scCO2) as the mobile phase. This project was divided into two parts. The first is the synthetic aspect that involves reacting an amino acid, in this case tyrosine, with dimethyl-tert-butyl-chlorosilane which substitutes onto the hydroxyl group to increase its solubility in scCO2. The synthesis, purification, and characterization of this novel molecule have been successfully completed. The second part of the project is the optimization of the chromatograph itself, necessitating a complete rebuild of an extant SFC. Much of the internal controls were bypassed or replaced; at this stage, the SFC is capable of injecting and detecting large organic compounds and amino acids. Research efforts are now focused on separating the silylated tyrosine from nonderivatized amino acids. Once achieved, the synthesis will be scaled up to include other amino acids and ultimately small peptides, which should separate more readily and provide identification of target proteins.
The implications of attention control on working memory span

(Georgia Institute of Technology, 2008-05-05) Gay, Catherine E.

Previous research has suggested that attention control is strongly implicated in working memory span. The current study utilized participants who had previously been tested for working memory capacity with the operation span, symmetry span and reading span tasks. Participants with high or low working memory spans where included in this study. These participants completed the Go/No-Go, Global/Local and Stop-Signal tasks, which examined different aspects of attention control. No significant differences were found between the working memory span groups on these three tasks.
Förster Resonance Energy Transfer and Fluorescence Quenching Based Low-density Lipoprotein Probes for Visualizing Transcytosis

(Georgia Institute of Technology, 2008-05-05) Fay, Nicole C.

Transcytosis is the process by which macromolecules are transported across a polarized cell. It is one of the main methods of nutrient absorption from the blood stream as well as the only means past the blood brain barrier. Insight into the transcytic route has enormous medical potential where drug delivery methods stand to be significantly optimized. Despite the importance of this fundamental biological process, the mechanism of transcytosis is not well understood. Previously, fluorescence microscopy has allowed the tracking of fluorescently labeled low-density lipoprotein (LDL) intracellularly. However, this labeled LDL is not able to distinguish LDL particles undergoing transcytosis versus degradation. LDL is an ideal cargo for observing intracellular processes due to its vital role in transporting cholesterol for cell membrane fluidity. In order to differentiate transcytosis from degradation, I have produced two probes sensitive to degradation. The two probes are based on the principles of 1.) Förster resonance energy transfer (FRET) and 2.) fluorescence quenching. LDL degradation of the FRET-based or the fluorescence-quenching-based probe results in a significant increase in fluorescent activity. I have used several methods to assess the functionality of these probes including fluorescence measurements of detergent and enzyme degradations, SDS-PAGE analysis of degradations, and in vivo flow cytometry. Additionally, I have optimized the growth conditions for maintaining polarity in a cell line (MDCK) known to undergo transcytosis. The time and location of LDL degradation in a cell can be resolved through the use of these probes. Future work includes single-particle tracking of LDL as it is being degraded versus actively transcytosing across a cell layer. This process is critical to understanding transcytosis as well as LDL regulation in the human body.
Sustained Delivery of Thermally Stabilized chABC by Lipid Microtubules

(Georgia Institute of Technology, 2008-05-05) Kumar, Nathan

Our knowledge of spinal cord injury repair is broadening with the developing technology for nerve regeneration and drug delivery. In this paper we discuss the current capabilities for spinal cord repair as well as those that are in development. We develop protocols for determining the thermal stability of chondroitinase ABCI and its ability to be implanted into a microtubule-hydrogel drug delivery vehicle as well as the release profile that results from this implantation. After the use of sodium dodecyl electrophoresis, we determined that the disaccharide trehalose has the capacity to thermally stabilize our therapeutic enzyme in vitro. We also determined that the microtubules are effective for sustaining the release of our enzyme while the hydrogel is effective for localizing its effects. The deactivation profile was experimentally quantified to allow for complete diffusion of our enzyme over the course of a two-week implantation. Our thermally stabilized enzyme and drug delivery system can be used for the purpose of facilitating nerve regeneration at the site of an injury.
Design of an actively cooled grid system to improve efficiency in inertial electrostatic confinement fusion reactors

(Georgia Institute of Technology, 2008-05-05) Seltzman, Andrew

Traditional inertial electrostatic confinement (IEC) fusion reactor designs utilize an ion accelerating grid fabricated out of a refractory metal capable of operating at high temperatures to radiate off heat imparted by ion-grid collisions. Unfortunately, the high gird temperature allows for a substantial thermionic electron emission current, requiring a high power draw and significantly reducing reactor efficiency. Further, electrons emitted from the grid are accelerated into the reactor shell where they generate a significant amount of bremsstrahlung x-rays requiring additional shielding and increasing system size and weight. Presented is a novel modification to the traditional implementation of IEC fusion reactor, designed to improve operating efficiency by reducing electron emission from the grid. A liquid cooled grid design is utilized to reduce thermionic electron emission, allowing for higher plasma densities, and greater input power while improving system efficiency and reducing x-ray output. The resulting low grid temperatures substantially reduce thermionic electron emission and greatly improve reactor efficiency by reducing current draw from the central grid. The reduction of thermionic electron emission will eliminate the majority of bremsstrahlung x-ray generation thereby reducing shielding requirements. By measuring the heat deposited into the coolant, the grid cooling system may also be used as a diagnostic tool to study the physics involved in IEC reactors. In this manner, grid transparency may be directly measured as a function of ion bombardment heating. By modifying the confinement scheme of the reactor and subsequently evaluating the energy flux to the grid through ion collisions, greater energy and particle confinement times may be obtained.