Thesis (M.S.)--State University of New York at Binghamton, Biological Sciences Department, 2007. / No. "15" in title is in superscript, or elevated, position. Includes bibliographical references.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 202-219). Also available via the Internet.

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M. S.)--Biology, Georgia Institute of Technology, 2009. / Committee Chair: Joseph Montoya; Committee Member: Ellery Ingall; Committee Member: Emanuele DiLorenzo; Committee Member: Marc Weissburg; Committee Member: Mark Hay.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 110-121).

Magister Scientiae - MSc / Geobacillus pallidus RAPc8 is a thermophilic nitrile-degrading isolate, obtained from thermal sediment samples of a New Zealand hot spring. The G. pallidus RAPc8 NHase gene has been cloned and expressed in E. coli. The recombinant NHase exhibits nitrile-degrading activity at 50 °C, capable of degrading branched, linear and cyclic heteroaromatic nitrile substrates. However, no activity was found on homoaromatic nitrile substrates such as benzonitrile. In the present study, high levels of activity on benzonitrile were detected with a double mutant βF52GβF55L. Kinetic analysis on the mutant enzyme showed an 8-fold decrease in KM with benzonitrile (0.3mM) compared to acrylonitrile (2.6mM). Specificity constants (kcat/KM) of 5900 and 450 s-1.mM-1 were obtained for the double mutant on benzonitrile and acrylonitrile respectively. The amino acid residues lining the substrate channel were identified and the geometric dimensions measured. Cavity calculations revealed a 29% increase in volume and a 13% increase in inner surface area for the substrate channel of the double mutant when compared to the wild type. Surface representation of the wild type structure revealed two extended, curved channels, which are accessible to the bulk solvent from two locations in the heterodimer. The removal of the βF52may have contributed to the presence of a single channel with two opposing openings across the dimers with no internal blockage. Normal Mode Analysis calculations also indicate a higher intrinsic flexibility of the mutant relative tothe wild type enzyme. The increased flexibility within the mutant NHase could have introduced a functionally relevant aromatic substrate recognition conformation. / South Africa

Magister Scientiae - MSc / In this study G. pallidus RAPc8 NHase mutants were screened for reduced substrate inhibition compared to the wild type enzyme. Wild type and mutant enzymes were expressed and purified using hydrophobic interaction chromatography. Amidase coupled enzyme stop assays were conducted using 3-cyanopyridine as a substrate, whereas continuous enzyme kinetics were conducted using acrylonitrile as a substrate. / South Africa

Trichodesmium is a globally significant marine diazotroph responsible for supplying new nitrogen to the oligotrophic regions in which it is found. Though it has been studied for decades, our understanding of the ways in which environmental factors can affect its nitrogen fixation rate remains limited. A continuous culture of Trichodesmium was established in which steady state growth and nitrogen fixation were maintained at dilution rates ranging from 0.27 to 0.67 d-1. Our results clearly show that, as growth rate increased, biomass decreased linearly and nitrogen fixation rate increased linearly. C:N:P ratios remained constant over the range of growth rates studied, suggesting a tight coupling between macronutrient uptake and the maintenance of balanced growth at steady state. We used cultures at steady state to determine the impact of nitrate exposure and uptake on nitrogen fixation. Nitrate inhibits nitrogen fixation by up to 70% in a concentration-dependent manner at initial nitrate concentrations less than 10?? Nitrate uptake accounted for as much as 86% of total N uptake and, at initial nitrate concentrations greater than 2.5 ??more than made up for the observed inhibition of nitrogen fixation. A field study of this diazotroph shows that nitrogen fixation scales with light intensity from a maximum at 50% surface irradiance. Estimated areal nitrogen fixation rates in the Gulf of Mexico, based on vertical abundance profiles and the relationship between nitrogen fixation and surface irradiance, are comparable to measurements made in other oligotrophic regions. Stable isotopic composition of the particulate organic matter and the zooplankton confirms that Trichodesmium nitrogen and carbon are moving into the food chain and are important to higher trophic levels. As much as 60% of the zooplankton carbon was derived from Trichodesmium. Our work established that this diazotroph is ecologically important in the water column of the Gulf of Mexico, with important implications for nitrogen and carbon cycling. Findings from our field and culture studies can be added to models used to quantify the importance of Trichodesmium nitrogen fixation on an oceanic scale.

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