Thesis (M.S.)--University of Wisconsin -- La Crosse, 1984. / Includes bibliographical references (leaves 54-59).

Thesis (M.E.E.)--University of Delaware, 2006. / Principal faculty advisor: Javier Garcia-Frias, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

Thesis (M.S.)--University of North Carolina at Greensboro, 2006. / Title from PDF title page screen. Advisor: Karen Katula; submitted to the Dept. of Biology. Includes bibliographical references (p. 70-77).

Thesis (M. Sc.)(Chemistry)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

Escherichia coli has served as a model organism for studies in molecular genetics and physiology since the 1960s. Yet the function of 20% of the 4288 known and predicted proteins in E. coli is still not known. Almost two-thirds of these proteins have homologs in other microorganisms, but their function(s) is not known in any organism. One such protein is YciG. YciG was chosen as the focus of this study because, intriguingly, an ortholog of YciG is found in the genome of the fungus Neurospora crassa. The gene encoding YciG is predicted to be in an operon with two other genes, yciF and yciE. Genes in the same operon often encode proteins with related functions, so the study was extended to include YciF and YciE. To determine the function of these proteins, in-frame deletion alleles were constructed and strains lacking one or more of the three proteins were tested for mutant phenotypes. Expression of the yciGFE operon is induced by several stresses and is regulated by RpoS, which controls the general stress response in E. coli. Therefore, we tested the ability of the mutant strains to survive environmental stresses. Our results revealed that YciG was important for stationary-phase resistance to thermal stress, oxidative stress and, in particular, acid stress. Both RpoS-dependent and RpoS-independent acid resistance mechanisms are found in E. coli. YciG was shown to be required for RpoS-independent acid resistance, but further experiments are needed to determine whether YciG also is required for RpoS-dependent acid resistance. YciG was not required for normal exponential growth of E. coli, as mutants lacking YciG had the same growth rate as the wild-type parent. No mutant phenotypes have been found yet for mutants lacking YciF or YciE. yciE deletion mutants showed the same growth rate and the same level of acid resistance as wild-type cells. The acid resistance of yciF mutants has not yet been tested, and strains lacking YciE and/or YciF need to be assayed for their ability to survive stresses other than acid stress.

The conductivity created in acid fracturing is a competition between two phenomena: etching of the rock surface and weakening of the rock. This study presents experimental results of acid fracturing conductivity experiments with polymer gelled acid, while varying contact time and rock type. The experiments were conducted in a laboratory facility properly scaled from field to laboratory conditions to account for the hydrodynamic effects that take place in the field. The rocks of study were Indiana limestone, San Andres dolomite and Texas Cream chalk. Our results illustrate that acid fracturing conductivity is governed by the etching pattern of the rock surface and influenced by the hardness of the rock. If channels are created, the fracture is more likely to retain conductivity after closure. The hardness of the rock is the dominating factor to determine the conductivity response when no channeling is present. Among the rocks tested, Texas Cream chalk had the lowest hardness measurement before and after acidizing and the fracture closed at a much lower stress compared with limestone and dolomite. Dolomite had the highest conductivity under all closure stresses even without a channeling pattern. Additionally, it was observed that a higher reduction in rock strength at the contact points for dolomite yielded lower conductivity after closure. The effects of hardness variation on conductivity are higher in dolomite than in limestone and chalk. It is apparent that longer contact times do not always provide higher conductivity after closure.

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There are increasing concerns that exposure to unmetabolized folic acid, which results from folic acid intakes that overwhelm the liver’s metabolic capacity, may be associated with adverse effects. In this study, we examined the folic acid status of women of reproductive age in relation to dietary intake and the effect of folic acid supplementation (1.1 mg or 5 mg). Plasma unmetabolized folic acid was not significantly correlated with folate intake estimated by food frequency questionnaire or biomarkers. The proportion of women with detectable levels of unmetabolized folic acid increased from 65% to 100% after twelve weeks of supplementation (p < 0.05), however, the increase in concentrations did not reach statistical significance and the effect was not sustained. Moreover, there were no significant differences between the two doses. This suggests that there are mechanisms by which the body adapts to high folic acid intakes to limit exposure to unmetabolized folic acid.

The effects of high maternal folate status on the offspring are unknown; however, early life exposure to environmental stimuli, including dietary factors, is thought to influence the risk of developing chronic disease. An animal study was performed to determine the effect of maternal folic acid supplementation during pregnancy and lactation on DNA methylation and global gene expression patterns in the offspring. Supplementation of the maternal diet with folic acid (5, 8, and 25 mg/kg diet) induced global DNA hypomethylation in the liver of juvenile and adult offspring, and altered the expression of the imprinted H19 gene and genes involved in lipid metabolism, coagulation, and iron transport and homeostasis. Our data suggest that intrauterine and early postnatal periods are susceptible to changes in DNA methylation and gene expression in response to high levels of folic acid, which may be associated with health status and disease later in life.

There are increasing concerns that exposure to unmetabolized folic acid, which results from folic acid intakes that overwhelm the liver’s metabolic capacity, may be associated with adverse effects. In this study, we examined the folic acid status of women of reproductive age in relation to dietary intake and the effect of folic acid supplementation (1.1 mg or 5 mg). Plasma unmetabolized folic acid was not significantly correlated with folate intake estimated by food frequency questionnaire or biomarkers. The proportion of women with detectable levels of unmetabolized folic acid increased from 65% to 100% after twelve weeks of supplementation (p < 0.05), however, the increase in concentrations did not reach statistical significance and the effect was not sustained. Moreover, there were no significant differences between the two doses. This suggests that there are mechanisms by which the body adapts to high folic acid intakes to limit exposure to unmetabolized folic acid.