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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Now showing 1 - 7 of 7
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    Characterization of a novel Escherichia coli exopolysaccharide and its biosynthesis by NfrB
    (2024) Fernando, Sashika Hansini Lakmali; Poulin, Myles B; Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Biofilms are made from an association of bacterial cells and extracellular products dominated by a plethora of exopolysaccharides. Accumulating evidence have demonstrated that the bacterial second messenger cyclic-di-guanosine monophosphate (c-di-GMP) promotes the synthesis of these exopolysaccharides through direct allosteric activation of glycosyltransferase enzymes. The Escherichia coli inner membrane protein NfrB, which together with the outer membrane protein NfrA acts as a receptor system for phage N4, contains a N-terminal glycosyltransferase domain and C-terminal c-di-GMP binding domain. Recent research revealed that NfrB is a novel, c-di- GMP controlled glycosyltransferase that is proposed to synthesize a N-acetylmannosamine containing polysaccharide product, though the exact structure and function of this remains unknown. Nfr polysaccharide production impedes bacterial motility, which suggests a possible role of the Nfr proteins in bacterial biofilm formation. Here, we carry out in-vivo synthesis of novelNfr polysaccharide followed by its structural characterization. Preliminary data from MALDI- TOF mass spectrometry and Solid State 13C NMR spectroscopy indicated that the Nfr polysaccharide is mainly a homo polymer of poly-?-(1®4)-N-acetylmannosamine, bound to an aglycone. In addition, we report efforts to develop of a Nfr polysaccharide binding and detection tool, through the mutation of YbcH, a putative Nfr polysaccharide hydrolase enzyme. These studies advance the understanding of Nfr polysaccharide biosynthesis and could offer potential new targets for the development of antibiofilm and antibacterial therapies.
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    TWO MARINE SPONGES, LENDENFELDIA CHONDRODES AND HYMENIACIDON HELIOPHILA, AND THEIR MICROBIAL SYMBIONTS: ROLES IN MARINE PHOSPHORUS CYCLING.
    (2021) Jonas, Lauren; Hill, Russell; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Marine sponges have emerged as major players within coral reef biogeochemical cycles, facilitating intake and release of carbon, nitrogen, and phosphorus. The majority of studies have investigated the role of sponges in transforming dissolved carbon and nitrogen; however, the same breadth of insights has not been extended to phosphorus. This study uses 32P-labeled orthophosphate and ATP to determine that two marine sponges, Lendenfeldia chondrodes and Hymeniacidon heliophila, both rapidly take up ambient dissolved inorganic phosphate and dissolved organic phosphorus. Subsequent genetic analysis and chemical extraction showed that sponge symbionts store phosphorus in the form of energy-rich polyphosphate (poly-P). L. chondrodes, a sponge from oligotrophic habitats and with a microbiome dominated by cyanobacterial symbionts, stores more phosphorus as poly-P (6–8%) than H. heliophila (0.55%), a eutrophic sponge with low cyanobacterial abundance. This work adds new insights to the roles of the sponge holobiont in cycling the crucial element, phosphorus.
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    Analysis of Flow-Based Microfluidic Gradient Generators for the Study of Bacterial Chemotaxis
    (2015) Wolfram, Christopher James; Rubloff, Gary W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Chemotaxis is a phenomenon which enables cells to sense concentrations of certain chemical species in their microenvironment and move towards chemically favorable regions. This behavior is best understood in the bacteria Escherichia coli, which exhibits chemotaxis towards a variety of energy sources and signaling molecules. Recent advances in microbiology have engineered the chemotactic properties of bacteria to perform novel functions, but traditional methods of characterizing chemotaxis are not sufficient for such complex applications. The field of microfluidics offers solutions in the form of gradient generators. Many of these gradient generators are flow-based, where a chemical species diffuses across a solution moving through a microchannel. A microfluidic gradient generator was explored as a chemotaxis platform. Sources of error during experimental operation and methods of mitigating this error were demonstrated, and the fundamental theory behind these devices was examined. These devices were determined to be inadequate for the study of bacterial chemotaxis.
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    MICROBIAL INTERACTIONS AND ECOLOGY WITHIN BLOOMS OF THE TOXIC DINOFLAGELLATE KARENIA brevis ON THE WEST FLORIDA SHELF.
    (2013) Meyer, Kevin Anthony; O'Neil, Judith M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The dinoflagellate Karenia brevis is capable of significant ecological and economic impacts in Florida waters where blooms typically occur. Blooms and cultures of K. brevis were sampled to determine the composition, production, and possible ecological function of bacteria and virus communities associated with K. brevis. Bacterial communities on the West Florida Shelf (WFS) were similar inside and outside K. brevis blooms, but primary and secondary (bacterial) production and bacteria and virus abundances were different depending on bloom stage. Bloom stages need to be identified so that discrete sampling events can be combined to characterize an entire bloom event. Within an initiating bloom bacterial production and mortality was high and viral abundance was low, suggesting that viral genomes were either within host cells or bacterial mortality was due to mixotrophic grazing by K. brevis or heterotrophic nanoflagellates. In a maintenance phase bloom the bacterial community was metabolically stressed, subject to increased viral infection, and most likely not being subjected to mixotrophic grazing. Bacterial communities associated with healthy K. brevis were dominated by the Cytophaga-Flavobacterium-Bacteroides (CFB) complex. As K. brevis shifted to stationary or senescing growth communities had higher proportions of Alphaproteobacteria. The SAR406 group, typically found in deep waters, was present in the surface waters of the WFS which supports existing K. brevis bloom formation hypotheses involving upwelling of deep waters from the mid to outer shelf. The CFB complex of bacteria also need to be further investigated as the consistent presence of CFB bacteria in both blooms and cultures of K. brevis suggest CFB bacteria are capable of numerous interactions with K. brevis. Furthermore, such interactions may be a vector of bloom control through viral infection; a high proportion of CFB bacteria would be ideal for density-dependent viral infection which could disrupt interactions between bacteria and K. brevis. Inoculating cultures of K. brevis, which included associated bacteria, with viral concentrates from the WFS showed differences in bacterial production and growth which indicate viruses are acting upon the bacterial community and not the dinoflagellates. Interactions between bacteria and K. brevis need to be further elucidated and explored for a better understanding of the role of each in dynamics of this harmful algal species. There may be a natural community succession amongst bacteria during blooms: utilizing certain indicator species to indicate bloom stage and transition between stages may aid in bloom forecasting and detection efforts.
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    Intact bacterial hopanoids as specific tracers of bacterial carbon in marine and estuarine environments
    (2009) Taylor, Karen Ann; Harvey, H. Rodger; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Intact bacteriohopanepolyols (BHPs) and their degrative products were investigated in surface sediments and particulate organic matter from the Bering Sea, Western Arctic Ocean and Chesapeake Bay to trace the inputs of bacterial carbon sources and the dominant microbial processes operative during organic matter recycling. Despite cold temperatures and the dominance of diatoms, cyanobacteria are ubiquitous and inhabit the deeper layers of the euphotic zone in the Bering Sea, where their contributions to sediments were directly traced. As a small but important contribution to the total system chlorophyll, cyanobacteria represent a previously undocumented fraction of the organic carbon pool in this region. In the Western Arctic, soil derived bacterial sources were abundant and include a fraction that likely degraded on land prior to being transported into the Arctic Ocean. Bacterial signatures in Chesapeake Bay transition along the salinity gradient with intact hopanoids reflecting a diverse range of potential bacterial sources.
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    Efforts Toward Synthesis of Novel Analogs of the Bacterial Second-Messenger, c-di-GMP
    (2009) Shurer, Andrew Joseph; Sintim, Herman O; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The formation of bacterial biofilms is a common mechanism for antibiotic resistance. It has been shown that bis-(3'-5')-cyclic dimeric guanosine monophosphate, c-di-GMP, plays a key role in bacterial biofilm formation; therefore, the proteins that regulate the metabolism or adaptive response of c-di-GMP are favorable targets for novel antimicrobials. We herein describe a solid-support methodology developed in the Sintim Laboratory and efforts toward its application to the synthesis of novel c-di-GMP analogs. Our selected targets are a series of analogs bearing various substitutions at the 2'-position of the ribose backbone. Syntheses of 2'-deoxy and 2'-methoxy analogs were achieved as well as that of key intermediates toward the 2'-fluoro and conformationally flexible analogs.
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    Regulation of estuarine phytoplankton and bacterial urea uptake and urease activity by environmental factors
    (2006-11-13) Solomon, Caroline Miller; Glibert, Patricia M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The regulation by environmental factors of two enzymes involved with urea utilization - urea transport and urease - in estuarine phytoplankton and bacteria was studied in cultures of five phytoplankton species, in Chesapeake Bay and Choptank River assemblages, and in bioassay and mesocosm experiments. In these experiments, temperature and nitrogen availability (NO sub 3 minus, NH sub 4 plus, and urea) were found to regulate urea uptake and urease activity. However, regulation by these environmental factors was dependent on the composition of the plankton community. Dinoflagellates were found to have the highest urease activity in culture among five phytoplankton species (Prorocentrum minimum, Karlodinium veneficum, Heterocapsa triquetra, Storeatula major, and Isochrysis sp.) in culture on a per cell and per cell volume basis with an optimized method to measure urease activity. Urease activity was also lower when the dinoflagellates were grown on NH sub 4 plus than when grown on NO sub 3 minus or urea, suggesting repression by NH sub 4 plus. Higher rates of urea uptake and urease activity in Chesapeake Bay and the Choptank River were often associated with the presence of dinoflagellates and cyanobacteria during the warmer months. Rates were also higher under N-limitation when these phytoplankton were present than under P-limitation when diatoms were present. Rates of urea uptake and urease activity in natural assemblages were repressed when NO sub 3 minus and NH sub 4 plus concentrations exceeded 40 and 5 ug at N l to the negative 1, respectively. Rates of urea uptake and urease activity decreased in response to additions of NH sub 4 plus in bioassay and mesocosm experiments. In these experiments, dinoflagellates had the highest urea uptake and urease activity on a per cell basis while cyanobacteria had the highest urea uptake and urease activity on a per cell volume or per chlorophyll a basis. The difference in regulation of urea uptake and urease activity among the diatoms, dinoflagellates and cyanobacteria provide some biochemical explanantions about how they utilize urea under contrasting environmental conditions.