No description available.

No description available.

No description available.

Candida albicans colonizes the gastrointestinal tract of up to 75 % healthy individuals. It usually cohabits the gut as an innocuous commensal. But in critically ill patients whose gut barrier, immune system and normal gut microbiota are compromised, C. albicans often transmigrates the gut barrier, transforms into an invasive pathogen and causes fatal systemic infections. The genetic transitions that drive this transformation in C. albicans have been a major focus of research and have led to the identification of key transcription factors that regulate this commensal-to-pathogen transition. However, the current challenge lies in identifying the downstream pathways and effectors that bring this transition into effect. This thesis addressed this challenge by developing 11 new bioinformatics tools, including 6 comprehensive databases, 4 novel software packages and 1 analysis framework. These databases included a comprehensive topological map of the mammalian gut biogeography, a C. albicans microarray database comprising of 3,091 publically available microarray transcript profiles, C. albicans RNA-seq gene expression and small variant databases extracted from 1,177 publically available RNA-seq samples, a C. albicans gene alias database comprising of 113,297 gene aliases representing the 6,735 open reading frames of C. albicans, and a C. albicans gene ontology slim comprising of 1,194 C. albicans-specific gene ontology terms. These databases were accompanied by a robust analysis framework which brought together these resources for quality control, batch correction and weighted gene co-expression network analysis. All these tools were finally employed in a pilot exploration of the C. albicans gut commensal-to-pathogen transition, which demonstrated the effectiveness of these bioinformatics resources. The analysis unveiled known regulators, uncharacterized gene networks, pathways and effectors potentially crucial for the C. albicans gut commensal-topathogen transition. These resources are a step towards a better understanding of this transition and can also be utilized for examining various other aspects of C. albicans biology.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

published_or_final_version / Microbiology / Master / Master of Philosophy

Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 44.

No description available.

No description available.

Phytophthora parasitica, P. citrophthora, and other plant pathogenic fungi were isolated from re-cycled water used to irrigate citrus and other crops. The several propogules of P. parasitica were then studied to determine their survival capabilities in soil and irrigation water. Chlamydospores of P. parasitica were present in field soils from foot-rot infested citrus groves and persisted for at least 60 days in air-dried or moist soils. They germinated in irrigation water or moist soil and formed sporangia within 16 hr. Sporangia were also present in these field soils and survived for at least 60 days in moist soil. They germinated, releasing zoospores into irrigation water 5 min after being inundated. Zoospores were not present in water flooded on air-dried field soil until after 20 hr incubation. Citrus leaves became infected by zoospores within 15 min when placed in zoospore infested water. Although they remained motile in irrigation water for up to 20 hr at 20 C, zoospores encysted when agitated or upon the addition of nutrients, orange peel, or citrus leaves. At low nutrient levels (< 5 mg glucose/liter of sterile distilled water) zoospores germinated and upon cessation of growth the protoplasm contracted within the hyphae and pseudo-septa were formed. Empty cysts or hyphae often lysed; remaining hyphal fragments containing protoplasm survived for at least 40 days at 25 C in untreated waste water and resumed growth upon addition of nutrients. At higher nutrient levels (10-1,000 mg glucose/liter of sterile distilled water) the hyphal tips often produced appressorium-like structures when in contact with the container surface. Exudates from orange peel or citrus leaves stimulated similar activity. The appressorium-like structures usually germinated to produce microsporangia when the nutrients were replaced with untreated irrigation waste water. Some microsporangia persisted in untreated waste water at 25 C for 60 days but most germinated sooner, producing only a single zoospore. Mycelial inoculum from these zoospores was pathogenic to roots of citrus seedlings. Results indicate that P. parasitica is spread by re-cycled irrigation water and that zoospores, or structures produced by them, can play a significant role as survival or dispersal units in re-cycled water.