Thesis (Ph. D.)--University of Wisconsin--Madison, 1960. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 42-49).

Photocopy of typescript. / Digitized by Kansas Correctional Industries

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Calcium has been shown to play important roles in the control of tip growth in a wide range of cell types. This thesis sets out to test the effects of exogenous Ca2+ on various morphological events during the life cycle of the human pathogenic fungus Aspergillus fumigatus. The Ca2+ chelating agent EGTA induced marked morphological effects on colonies of A.fumigatus. That is radial growth rate decreased and branching frequency increased with increasing concentration of EGTA. Ion substitution experiments indicated that these effects were due to the chelation of Ca2+ and not Mg2+, Zn 2+, Cu2+ or Fe2+. However, Mn2+ was able to substitute for Ca2+. Calcium ions were required for germ tube emergence but not for the preceding period of spherical growth in spores of A.fumigatus. That is the rate of spherical growth was independent of exogenous [Ca2+ ] but germ tube emergence was retarded and spores became more swollen as exogenous Ca2+ decreased. The effect of applied electrical fields on spores of A.fumigatus was investigated. Germ tubes were anodotropic and polarisation increased with increasing field strength. The galvanotropic response was dependent on Ca2+ and polarisation decreased with exogenous [Ca2+ ]. The effect of exogenous [Ca2+] on growth kinetics of colonies of A.fumigatus growing on solid medium was investigated. When colonies were incubated on medium buffered at pCa 4-8 (10-4-10 -8 M) hyphal growth unit length and mean hyphal extension rate decreased linearly with the log of Ca2+ concentration. In contrast the specific growth rate remained constant over the range pCa 4-7 and was only reduced when colonies were incubated in medium buffered at pCa 8. This suggests that exogenous Ca2+ acts on processes that govern apical growth and branching but do not affect growth per se. The effect of a broad range of Ca2+-channel blockers and calmodulin antagonists on the growth and morphology of colonies of A.fumigatus were also investigated.

The pressing need for clean renewable energy sources has aroused worldwide research interest on the exploration of biofuels produced from lignocellulosic feedstock (e.g. forestry or agricultural residues and municipal wastes). The general absence of cost-effective method to overcome the recalcitrant nature of cellulosic biomass is the major challenge for the industrialization of this so-called second-generation biofuel. With the purpose to enhance our understanding of the fundamental mechanism of thermophilic microbial cellulose conversion process, we used culture-independent metagenomic analysis based on Next Generation Sequencing to explore the physiological ecology of thermophilic cellulolytic microbial community and more importantly to discover metabolic potentials. During the enrichment of thermophilic cellulolytic consortium, noticeable effects of co-substrate and pH was observed and subsequently investigated. Based on the community structure revealed by 16S rRNA gene sequencing at various pH values, we concluded that keeping pH higher than 6.0 was crucial to maintain effective cellulose conversion because the growth of Thermoanaerobacterium over other more efficient cellulolytic populations could be practically avoided. Given in mind that uncharacterized microbial populations may possess critical enzymatic components that are essential for the breakdown of cellulosic feedstock, gene-centric metagenomic pipeline was developed to discover genes that are functionally beneficial for thermophilic cellulose hydrolysis. Aside from that, metagenomic gene mining based on functional prediction using HMM (Hidden Markov Model) showed higher positive ratio in identifying novel carbohydrate-active genes than that of functional screening. Without cultivation, near complete genomes of the major thermophilic cellulose degraders were recovered from the metagenome by a gene binning pipeline combining tetranucleotide frequency based primary k-means clustering and subsequent scaffolding with paired-end relationship between two reads (sequences). Furthermore, by quantifying the transcriptional activities of various carbohydrate-active genes in the metatranscriptome of the enriched thermophilic cellulose-degrading consortium, we disclosed significance of enzymes of GH09 and GH48 which had been underestimated by previous metagenomic studies. Eventually, metagenomic survey of various sludge samples collected at specific operational conditions helped to confirm the metabolism potential of thermophilic sludge in cellulose up taking by possessing more enzymes of GH05 and GH04 families. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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Thesis (Ph.D.) in Biochemistry and Molecular Biology--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 117-133).

Diss. (sammanfattning) Stockholm : Univ., 2004. / Härtill 7 uppsatser.