Electronic Theses and Dissertations (PhDs)

Permanent URI for this collectionhttps://hdl.handle.net/10539/38017

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Start date: 2019End date: 2019

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    Insight into the genomic architecture of a South African entomopathogenic nematode and its associated bacterial symbiont
    (University of the Witwatersrand, Johannesburg, 2019) Naidoo, Stephanie; Gray, Vincent M.
    Nematoda is one of the most prolific and biologically-diverse of all animal phyla, with species adopting lifestyles ranging from free-living to parasitic. Among the diversity of parasitic nematodes lies a specialized group known as entomopathogenic nematodes that features the ability to rapidly kill insect hosts facilitated through a mutualist association with insect pathogenic bacteria. South Africa offers a range of undisturbed habitats that plays host to a great diversity of plant and insect species. Therein lies an opportunity for the recovery of novel entomopathogenic nematode species with a greater tolerance towards local environments and insects, which could potentially be exploited for biological control. In this study, a small-scale survey was conducted in the Gauteng province of South Africa in 2014, which led to the isolation of a new steinernematid, Steinernema sp. HBG28 and its associated bacterial symbiont, Xenorhabdus khoisanae strain MCB. It was found that phase I and phase II variants of X. khoisanae strain MCB featured the ability to swarm on solid agar. This is the first report of swarming behaviour observed in Xenorhabdus bacteria undergoing phenotypic variation. Genomic sequencing was performed on X. khoisanae strain MCB, revealing a genome of 4,6 Mbp in length with 3,869 protein- coding genes, of which, fourteen genes were specifically implicated in flagellar motility. Comparative genomic analyses with other Xenorhabdus spp. indicated the presence of these flagellar motility genes, with the exception of two chemotaxis genes found only in X. khoisanae (cheA and cheY), suggesting that these genes may be necessary in bacterial swarming during phase variation. Additionally, a draft genome assembly of Steinernema sp. HBG28 was produced, which was 97 Mbp in length and consisted of 35,869 predicted protein-coding genes, 1,281 tRNAs and 43 rRNAs. Further genomic characterization of Steinernema sp. HBG28 confirmed its mutual role iii in insect pathogenicity along with its bacterial symbiont. This study was unique as it represented the first genomic characterization of a new Steinernema entomopathogenic nematode species and its associated bacterial symbiont in South Africa. Furthermore, this study paves the way for further research into the biological mechanisms involved in host-parasite and host-symbiont interactions.
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    Investigating 2-hydroxypropyl-β-cyclodextrin (HPβCD) as a novel therapeutic agent for breast cancer
    (University of the Witwatersrand, Johannesburg, 2019) Saha, Sourav Taru; Kaur, Mandeep
    Cancer cells have an increased need for cholesterol, which is required for cell membrane integrity. Cholesterol accumulation has been described in various malignancies including breast cancer. Cholesterol has also been known to be the precursor of estrogen and vitamin D, both of which play a key role in the histology of breast cancer. Elevated cholesterol levels have been linked to breast cancer therefore depleting cholesterol levels in cancer cells can be a viable strategy for treatment. 2-hydroxypropyl-β-cyclodextrin (HPβCD) is a cholesterol depleting compound which is a cyclic amylose oligomer composed of glucose units. It solubilizes cholesterol and is proven to be toxicologically benign in humans. This led us to hypothesise that it might deplete cholesterol from cancer cells and may prove to be a clinically useful compound. Our work provides experimental evidences to support this hypothesis. We identified the potency of HPβCD in vitro against two breast cancer cell lines: MCF7 (Estrogen positive, ER+), MDA-MB-231 [Triple negative breast cancer (TNBC)], and compared the results against two normal cell lines: MRC-5 (Normal Human Lung Fibroblasts) and HEK-293 (Human embryonic kidney) using cytotoxic, apoptosis and cholesterol based assays. HPβCD treatment reduced intracellular cholesterol resulting in significant breast cancer cell growth inhibition through apoptosis. The results hold true for both ER+ and TNBC. We have also tested HPβCD in vivo in MF-1 mice xenograft model and obtained 73.9%, 94% and 100% reduction in tumour size for late, intermediate and early stage TNBC. These data suggest that HPβCD can prevent cholesterol accumulation in breast cancer cells and is a promising anti- cancer agent