UMD Theses and Dissertations

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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 given thesis/dissertation in DRUM.

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Subject: search.filters.subject.cellulose

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Now showing 1 - 4 of 4
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    Processing and structural characterization toward all-cellulose nanocomposites
    (2021) Henderson, Doug A; Briber, Robert M; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Cellulose is the most abundant biopolymer on the planet and is used in a variety of industry sectors including paper, coatings, medicine, and food. A deep understanding of cellulose is important for its development as an alternative polymer to those based on petroleum. This work focuses on two cellulose systems. The first of these, cellulose nanofibers, are the basic structural elements of naturally-occurring cellulosic materials; they exhibit excellent mechanical characteristics due to high crystallinity and a dense network of hydrogen bonding. These fibers can be separated from bulk cellulose via a TEMPO oxidation reaction followed by mechanical homogenization into a suspension in water. In this work, the production of these fibers is investigated by monitoring the change in structure of cellulose as a function of TEMPO reaction time and mechanical homogenization using small angle neutron scattering, atomic force microscopy, and optical microscopy. The second cellulose system is a molecular solution of cellulose formed using a binary solvent mixture consisting of ionic liquid and an aprotic solvent. Cellulose is difficult dissolve due to a dense hydrogen bonding network, and ionic liquids have been shown to be an effective alternative to more hazardous and energy-intensive dissolution methods for cellulose currently used in industry. The phase behavior of these solutions has been investigated using small angle neutron scattering as a function of temperature. The process of regenerating cellulose from these solutions is also investigated, as dense gels of cellulose and ionic liquid were produced with a unique multiscale ordered structure. The ultimate goal of this work is to combine cellulose nanofibers and molecular cellulose solutions in order to create all-cellulose nanocomposite films. These films are characterized using tensile testing, atomic force microscopy, and water uptake measurements in order to understand the interaction between cellulose nanofibers and molecular cellulose solutions, water resistance and tunability of mechanical properties.
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    FIBER DIGESTION IN THE JUVENILE BLUE CRAB, CALLINECTES SAPIDUS RATHBUN
    (2006-01-24) Allman, Andrea Lauren; Place, Allen R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Five experiments were performed to determine the importance of chitin and cellulose in the diet of juvenile <em>C. sapidus</em>. A compartmentalized recirculating system was established to provide optimal conditions, maintaining the animals with little mortality. The appropriate ration, compartment size, and an adequate baseline diet were established. We replaced 20% of a commercial diet with varying amounts of chitin and cellulose. Crabs fed the cellulose-containing diet had higher growth rates, conversion efficiencies, molt increments and frequencies than crabs fed the chitin-containing diet, but were equal to the control diet. We then assayed for chitinase and cellulase in gut tissues. Chitinase had lower specific activity (0.072 + 0.159 mU mg-1min-1) than cellulase (3.52 + 0.16 mU mg-1min-1) in the foregut and hepatopancreas. There was no effect of diet on specific activity. The results show juvenile <em>C. sapidus</em> is capable of utilizing cellulose, but not chitin, when delivered as 20% of a diet.
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    DEGRADATION OF PLANT CELL WALL POLYSACCHARIDES BY SACCHAROPHAGUS DEGRADANS
    (2005-12-08) Taylor II, Larry Edmund; Weiner, Ronald M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    <em>Saccharophagus degradans</em> is an aerobic, Gram negative marine bacterium, isolated from decaying <em>Spartina alterniflora</em> in the Chesapeake Bay watershed. <em>S. degradans</em> can degrade and metabolize numerous complex polysaccharides, including the major components of the plant cell wall, cellulose, xylan and &#946;-glucan. Genomic analyses reveal that <em>S. degradans</em> has 77 genes coding for enzymes that are predicted to participate in the degradation of plant cell wall polysaccharides. These include complete, functional, multienzyme systems for the depolymerization of cellulose, xylan, arabinan, &#946;-1,3-glucans, &#946;-1,4-glucans, and mannan. Most of the cellulases are modular, some of which contain novel combinations of catalytic and/or substrate binding modules. In addition to its well-predicted plant wall degrading systems, <em>S. degradans</em> encodes 19 proteins which contain a carbohydrate binding module, but lack an identifiable catalytic domain and 12 glycanases for which function cannot be predicted by sequence analysis. Many of the plant wall degrading enzymes contain lipoprotein signature sequences, indicating that they are likely attached to the cell surface, thereby maintaining their reactions near the cell and preventing loss of enzyme or product to diffusion or competition. <em>S. degradans</em> is capable of using crystalline cellulose and intact plant matter as sole carbon and energy sources. Cellulose induces catalytic activity against all major plant cell wall polymers, suggesting a complex mechanism for coordinating the regulation of these multienzyme systems. In addition to its abundant carbohydrases, <em>S. degradans</em> encodes seven proteins with predicted molecular weights over 250,000 Daltons, one of which, CabA at 1,500,000 Daltons, is the largest known bacterial protein to date. These proteins contain calcium-binding repeat sequences suggesting a role in cell-tosurface adhesion or protein-to-protein interaction, perhaps as a means of surface enzyme attachment. These studies establish <em>S. degradans</em> as the first marine bacterium with a complete and functional cellulase system with the further ability to degrade plants in monoculture.
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    TOWARD A BETTER UNDERSTANDING OF THE CELLULAR, MOLECULAR AND GENETIC BASES OF THE RUGOSE MORPHOLOGY OF SALMONELLA TYPHIMURIUM
    (2005-08-05) Anriany, Yuda Adha; Joseph, Sam W; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The origin of rugose (wrinkled) colony morphology of Salmonella Typhimurium, which is formed only at stationary phase, low temperature, and under low osmolarity, is attributed to the production of an extracellular matrix and is associated with biofilm and pellicle formation, likely for survival strategies. The regulator CsgD is required for the synthesis of both matrix components: curli, encoded by the csgBAC operon, and cellulose, encoded by the bcs operon. Transcription of csgD, in turn, depends upon a number of transcriptional regulators such as SigmaS, OmpR and HNS. Using random mutagenesis, two groups of mutants with altered rugose phenotype were identified. The two mutations in the first group caused retardation of rugosity and altered waaG and ddhC, which are required for synthesis of the core and O antigen of lipopolysaccharide synthesis, respectively. Both mutants exhibited lack of motility, decreased levels of curli, and, especially in the waaG mutant, increased cellulose production. In media containing high osmolarity, both mutants produced more biofilms. Non-polar gene knockout and complementation performed on the waaG further confirmed these phenotypes in this transposon mutant. Thus, alteration in the LPS seemed to influence both curli and cellulose in opposing manners, and appeared to direct cells toward alternative pathways to produce biofilm matrix. The regulatory mutation in the second group affected hfq, and produced only minimal amounts of cellulose and curli protein. This phenotype was confirmed in an hfq deletion mutant. Transcriptional fusion between the csgB or csgD promoter and lacZ showed a drastic reduction in activity of both promoters in an hfq mutant compared to that in the wt. These were surprising results given the known function of Hfq as a post-transcriptional regulator, including in the regulation of SigmaS-encoding gene rpoS. However, when the promoter activity was measured in an rpoS hns background, where transcription continues under Sigma70, significant reduction was still shown in the hfq mutant. Deletion of the gene that codes for DsrA, a sRNA which, together with Hfq, is required for translation of rpoS at low temperatures, had minimal effect in both promoters. These results indicate that Hfq may regulate both promoters independent of SigmaS.