Thesis (Ph. D.)--Cornell University, August, 2006. / Vita. Includes bibliographical references (leaves 201-220).

Thèse d'exercice : Médecine. Médecine générale : Nantes : 2007. / Bibliogr.

Thèse (M.Sc.)--Université Laval, 2009. / Bibliogr.: f. 71-86. Publié aussi en version électronique dans la Collection Mémoires et thèses électroniques.

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

Allelic expression imbalance, or AEI, is the term given to differences in the expression levels of the two alleles of a gene. AEI has been previously identified in a number of species using various techniques. Here, the genome-wide extent of allelic expression imbalance in the pathogenic yeast species, Candida albicans, was examined through use of RNA sequencing in combination with a novel computational pipeline based around the diploid reference genome. Techniques for validating these results were investigated, and the difficulties surrounding specificity and quantification are discussed. As C. albicans is a highly heterozygous species, it was hypothesised that polymorphisms within alleles lead to differences in allele expression, which are further linked to differences in allele function. The functional consequences of AEI were therefore interrogated through investigation of Gene Ontology, identification of condition specific responses in AEI, and targeted construction and phenotypic screening of heterozygous knockout strains. Together, these results strongly suggest that divergence in allele expression is not linked to differences in allele function. Investigations of the possible control mechanisms behind the differences in allele expression were considered, with a focus upon structural factors such as chromosomal location, GC content, allele length and codon usage. However, issues with establishing causality are present, and difficulties lie in distinguishing between functional differences and consequences of bias in sequencing technologies. This piece of research has advanced the understanding of gene expression mechanisms within a medically important pathogen, paving the way for further investigations into the functional consequences of allelic expression imbalance in Candida albicans.

The main aim of this project was to study Candida albicans cell wall biosynthesis in response to stress. The role of the MAPK, Ca2+/calcineurin and cAMP/PKA signal transduction pathways in regulating the C. albicans cell wall stress response was investigated. A library of mutants lacking receptors, signalling elements and transcription factors were screened for alterations in their ability to respond to a range of cell wall stressing agents, including CaCl2, Calcofluor White and caspofungin. Pretreatment of wild-type cells with CaCl2 and CFW, activates the Ca2+/calcineurin and PKC pathways, leading to an increase in chitin content, and reduced susceptibility to caspofungin. Although elevation of cell wall chitin content often resulted in decreased sensitivity to caspofungin, I show here that some strains with increased chitin levels remained sensitive to caspofungin. The results show that elevation of chitin is a common property of a range of mutants that are affected in coordinating cell wall stress pathways, but that multiple mechanisms are likely to operate in maintaining the robustness of the C. albicans cell wall. Some of the mutant strains of the MAPK, Ca2+/calcineurin and cAMP signalling pathways showed evidence of paradoxical growth, whereby less inhibition was achieved by higher concentrations of antifungal drug. The role of chitin-related genes and stress signalling pathways in regulating C. albicans paradoxical growth was also investigated. Based on these results, more detailed analyses were performed to investigate the correlations between sensitivity and resistance to caspofungin, in relation to paradoxical growth. The MAPK-Mkc1 and the calcineurin pathways played major roles in the paradoxical growth effect. There was a proportional relationship between echinocandin concentration and the chitin content of the cell wall although the chitin content did not continue to be upregulated by the highest echinocandin concentration. Different echinocandins, carbon source, cell morphology and medium composition influenced the extent of paradoxical growth effect. The existence of paradoxical growth in resistant strains such as Fks1 also highlights association of paradoxical growth with resistance mechanisms.

No description available.

published_or_final_version / Dentistry / Doctoral / Doctor of Philosophy

This thesis is an investigation of the exopolysaccharides produced by Lactococcus lactis subsp. Cremoris JFR1 and the hyphal cell wall glucans of Candida albicans. L. lactis is an important organism in the dairy industry for the production of fermented dairy products and the exopolysaccharides have been shown to add textural qualities to the foods. C. albicans is a fungal pathogen responsible for the common yeast infection and many post-surgery complications in hospitals and can grow in both the yeast and hyphae form. Through a series of GC-MS, NMR and chemical degradation experiments three unique polysaccharides are discovered in the L. lactis samples giving a molecular basis to the textural qualities provided by these molecules. Additionally, several unique structural features are discovered on the C. albicans hyphal glucan providing possible explanations for the differing immune responses elicited by the hyphae form of the fungus.

Thesis (M.Tech.: Homoeopathy) - Dept. of Homoeopathy, Durban Institute of Technology, 2004 xxvii, 155 leaves / The aim of this in vitro study was to determine the effect of Commiphora molmol tincture prepared in 86% v/v ethanol, Hydrastis canadensis tincture prepared in 62% v/v ethanol and Warburgia salutaris tincture prepared in 62% v/v ethanol against Candida albicans (C. albicans) with 62% v/v ethanol, 86% v/v ethanol and fluconazole as the control agents, and to determine the Minimum Inhibitory Concentration/s (MIC/s) of the effective tincture/s using the disc diffusion assay.