Microbial, Biochemical and Food Biotechnology
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Browsing Microbial, Biochemical and Food Biotechnology by Subject "3-hydroxy C9:0"
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Item Open Access The role of cryptococcal 3-hydroxy fatty acids in mediating interspecies interactions(University of the Free State, 2016-01) Mochochoko, Bonang Michael; Sebolai, O. M.; Pohl, C. H.English: Cryptococcus neoformans is today recognised as an important human pathogen that has arisen from a non-pathogenic terrestrial fungus. Its interactions (specifically antagonistic interactions with other microbes (such as amoeba) in its natural habitat, soil, has led to cryptococcal cells evolving elegant offensive and defensive strategies to survive in nature. Importantly, these qualities seem to be maintained and activated whenever cryptococcal cells engage in antagonistic interactions with other cell types i.e. when in competition with Pseudomonas cells, which is the subject of chapter two, as well as when engaging in parasitism with macrophages, which is the subject of chapter three. Towards this end, in this dissertation, special attention was given to the role of the secondary metabolite, cryptococcal 3-hydroxy C9:0, in mediating the fate of C. neoformans when in contact with these other cell types. In chapter two, it was sought to explore the interactive outcome between cryptoccocal cells and Pseudomonas cells. Both cell types can, in their individual capacity, lead to the development of pneumonia. While the host body has optimal conditions (temperature, ambient air, etc.) to promote the growth of these two pathogens, their growth may be limited by the available nutrients within the confined space of the host lung. It is therefore reasonable to conclude that these microbes would engage in competition in order to exert territorial dominance over the other. To demonstrate this point in vitro, Pseudomonas cells were co-cultured with cryptococcal cells over a period of time. It was subsequently determined that cryptococcal cells dominated Pseudomonas cells. This domination manifested in a significant reduction (p = 0.05) in the number of Pseudomonas cells over a 24-h period. In order to determine if the observed domination could be as a result of the cryptococcal 3-hydroxy fatty acid, 3-OH-C9:0, negatively affecting the growth of Pseudomonas cells, Pseudomonas cells were (in a separate experiment) directly challenged with this molecule. And here it was shown that the growth of Pseudomonas cells was inhibited in a dose-dependent manner by increasing concentrations of this molecule. Importantly, 3-OH-C9:0 inhibited growth of Pseudomonas cells, possibly leading to their death, via altering their membrane function following the incorporation of this saturated molecule into the bilayer leading to a more rigid membrane. Taken together, these findings suggested cryptococcal 3-OH-C9:0 possesses antimicrobial properties, that when secreted into the extracellular environment, negatively affect the fate of surrounding microbes. In chapter three the role of 3-OH-C9:0 in mediating the function of macrophages was investigated. Macrophages are critical in clearing infecting or invading microbial cells through phagocytosis. However, phagocytosis is a receptor-mediated process that is governed by a balance between pro-signal molecules that promote phagocytosis and anti-signal molecules that inhibit it. Thus, it is not surprising that microbes would counter the action of macrophages by producing anti-signal molecules that would subvert the capability of macrophages to clear infecting cells. Critically, the designed macrophage-challenge study showed that 3-OH-C9:0 induced macrophages to produce the protein alpha-2-HS-glycoprotein. This protein is an anti-inflammatory modulator that is important in maintaining immunological homeostasis. This implies this protein counters the effects of pro-inflammatory modulators, which drive the T-helper 1 response in order to clear microbial infections. Furthermore, it was established that macrophages do not produce 3-hydroxy C9:0, and this highlighted that macrophages would not deliberately produce these anti-signal molecules in order to undermine their responsibility of clearing infections. Based on the findings reported in this dissertation, a picture emerges that clearly points that 3-hydroxy fatty acids are crucial to the survival and pathogenesis of cryptococcal cells. According to the Centers of Disease Control and Prevention, cases of disseminated cryptococcal infections remain a major cause of morbidity and mortality. Thus there are considered efforts to manage cryptococcal infections. The studies presented in the dissertation highlight 3-hydroxy fatty acid biosynthetic route as a potential target for controlling the pathogenesis of this medically important fungus. Towards this end, the usage of animals in modelling disseminated cryptococcal infections should be considered in order to clearly establish the therapeutic benefits of drugs such as aspirin, which has previously been shown to inhibit production of these molecules in a dose-dependent manner.