Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item VEGETATION PATTERNS IN DEPRESSIONAL RESTORED, NATURAL REFERENCE, AND PRIOR-CONVERTED WETLANDS IN THE USA MID-ATLANTIC COASTAL PLAIN.(2012) Yepsen, Metthea; Baldwin, Andrew; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Vegetation responds quickly to environmental changes, making it a useful tool for assessing the success of wetland restorations. Plant community composition was compared in 47 sites across the coastal plain of Maryland, Delaware, Virginia, and North Carolina, USA. Fifteen of the sites were isolated depressional wetlands (natural reference), 16 were farmed "prior-converted cropland" sites (ditched and drained former wetlands), and 17 were restored wetlands. Prior-converted sites were highly disturbed and dominated by non-wetland conventional row crops. Natural reference sites were dominated by native woody species and restored sites were dominated by herbaceous wetland species. Natural reference sites had lower Anthropogenic Activity Index scores, higher average coefficients of conservatism, and higher Floristic Quality Assessment Index scores than restored and prior-converted sites. Wetland restorations have succeeded in developing wetland plant communities, but have not developed plant communities that match natural reference wetlands. This is likely due to continued human disturbance, age, and a lack of proper propagules.Item The Effects of Low-Fat Diet and Exercise on C-Reactive Protein and Metabolic Syndrome: Findings from a Randomized Controlled Trial(2008-07-09) Camhi, Sarah Michelle; Young, Deborah R; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Background: Low-fat diet (D) and exercise (E) are recommended for reducing cardiovascular disease risk. However, the independent and combined effects of D and E on C-reactive protein (CRP) and metabolic syndrome (MS) are unknown. Purpose: The purpose of this dissertation was to examine the changes in CRP and MS between control (C), D, E and diet plus exercise (D+E). Methods: Men (n=197) and postmenopausal women (n=180) with elevated low-density lipoprotein cholesterol and reduced high-density lipoprotein cholesterol, were randomized into a one-year trial with four groups: C, D, E or D+E (Stefanick et al., 1998). Weight loss was not an intervention focus. This secondary data analysis evaluated stored plasma samples for high-sensitivity CRP. MS prevalence was retrospectively found using the NCEP-ATP III definition. CRP change (ΔCRP) was examined between intervention groups using ANCOVA. Differences between groups for MS at follow-up were retrospectively investigated using logistic regression. All analyses were stratified by gender and controlled for baseline values, body fat change and other appropriate covariates. Results: In women, ΔCRP was different between D+E vs. C (-0.7 ± 0.33 mg/L, p = 0.04) and D+E vs. E (-0.9 ± 0.32 mg/L, p = 0.004). Women also had a decrease in CRP within D+E (Δ log CRP 0.2 ± 0.035 mg/L; p = 0.0002). After the intervention, ΔCRP did not differ for men between or within treatment groups. MS at follow-up was not different between C, D, E or D+E in either men or women. In women with MS, ΔCRP was different between D+E vs. C (-1.3 ± 0.43 mg/L; p = 0.006), D+E vs. E (-1.1 ± 0.44 mg/L; p = 0.02), and D vs. C (-1.2 ± 0.43 mg/L; p = 0.009). In women with MS, CRP decreased from baseline within D+E (Δ log CRP 0.2 ± 0.039 mg/L; p=0.0008). At follow-up, there were no differences between or within groups for ΔCRP in men with MS, or men without MS and women without MS. Conclusion: D and D+E may be effective treatments for reducing CRP in women with MS. Further studies are needed to replicate results and clarify the influence of gender.Item Relationship between fish intake, omega-3 fatty acids, mercury, and risk markers of coronary heart disease (NHANES 1999-2002)(2006-07-24) Smith, Kimberly Michele; Sahyoun, Nadine; Nutrition; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Item AUTOINDUCER-2 (AI-2) MEDIATED QUORUM SENSING IN ESCHERICHIA COLI(2004-12-14) Wang, Liang; Bentley, William E; Hutcheson, Steven W; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bacteria have evolved complex genetic circuits to regulate their physiological activities and behaviors in response to extracellular signals. In a process termed "quorum sensing", or density-dependent gene regulation, bacteria produce, release and respond to certain signaling molecules termed autoinducers. The bacterial autoinducer-2 (AI-2) has received intense interest recently because the gene for its synthesis, luxS, is common in a large number of Gram-negative and Gram-positive bacterial species. In this study, the luxS controlled genes were identified in Escherichia coli K12 strain under two different growth conditions using DNA microarrays. Deletion of the luxS was shown to affect expression of genes involved in AI-2 transport (the lsr operon) and methionine biosynthesis (metE), and to a lesser degree those involved in methyl transfer, iron uptake, resistance to oxidative stress, utilization of various carbon sources, and virulence. The effects of glucose on extracellular AI-2 level were investigated further. It was shown that both AI-2 synthesis and uptake in Escherichia coli are subject to catabolite repression through the cAMP-CRP complex. This complex directly stimulates transcription of the lsr (luxS regulated) operon and indirectly represses luxS expression. Specifically, cAMP-CRP is shown to bind to a CRP binding site located in the upstream region of the lsr promoter and works with LsrR repressor to regulate AI-2 uptake. This study, for the first time, has shown that quorum sensing regulates specific activities in E. coli K12, and has elucidated regulatory mechanisms for AI-2 biosynthesis and transport in this organism. With a better understanding of AI-2/luxS mediated gene regulation, we may be able to develop strategies for harnessing AI-2 quorum sensing for our advantage in bioreactor studies and ultimately in control of the bacterial pathogenicity.