Browsing by Author "Dawson, Mark William"
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- ItemDisinfection and environmental studies on pathogenic free-living amoebae : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Microbiology at Massey University(Massey University, 1982) Dawson, Mark WilliamOver the last fifteen years, there has been an increasing awareness of sporadic cases of Primary Amoebic Meningoencephalitis (PAM), affecting primarily younger age groups and appearing in an acute fulminant form. The earliest positive case known, may have been in England in 1909. The pathogenic free-living amoebae (PFLA), which comprises the genera Naegleria and Acanthamoeba, are the causative organisms of PAM and Granulomatous Amoebic Encephalitis (GAE) respectively. PAM is a rapidly fatal disease affecting the central nervous system (CNS), and GAE although essentially confined to the CNS, may also take the form of granulomata in the liver, spleen, uterus and kidneys. A study on the disinfecting potential of Baquacil in axenic conditions, for comparison with the disinfecting potential of the chlorine, chlorine dioxide, ozone and Deciquam 222, showed that the order of effectiveness as amoebicides was Baquacil, chlorine, chlorine dioxide, ozone and Deciquam 222 in hard water. In soft water the order is Deciquam 222, Baquacil, chlorine, chlorine dioxide and ozone. Further study on the effect of Baquacil, chlorine and chlorine dioxide on amoebae, in conditions involving the use of a known Biochemical Oxygen Demand (BOD), a known bacteria concentration, and a combination of BOD and bacteria, confirmed Baquacil as a more effective amoebicide than chlorine, which in turn was more effective than chlorine dioxide. The concentrations of each disinfectant required were increased by the presence of a BOD, and of bacteria. The bacteria were preferentially destroyed over the amoebae with all three disinfectants. Baquacil resistant clones of Naegleria fowleri were isolated, although it is not known whether this resistance is due to genetic or physiological variation. Axenically and Monoxenically cultured amoebae were used, the latter to increase the resemblance of the amoebae to those found in the environment. Differences in survival rates were observed, the monoxenically cultured amoebae invariably having higher survival rates. Competition studies were done with Naegleria spp. and T.pyriformis on three bacteria species, after preliminary studies on the ability of the two protozoa to grow on eight species of bacteria. Of the three bacteria used in the competiton studies, Escherichia coli and Enterobacter cloacae were shown to support both Naegleria spp. and T.pyriformis, with the ciliate increasing in numbers by up to 3 fold over the controls, but the amoebae were affected only slightly, with a small decrease in numbers compared to the controls. A synergistic relationship was evident on the third bacteria species, Pseudomonas fluorescens, between Naegleria spp. and T.pyriformis, where as in the controls, this bacterium was not a good growth support bacteria for either protozoan.
- ItemA study of citric acid production by submerged aerobic fermentation using the fungus Aspergillus niger : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biotechnology at Massey University(Massey University, 1986) Dawson, Mark William; Dawson, Mark WilliamThe aim of this work was to obtain detailed information on the production of citric acid during submerged fermentation by Aspergillus niger, in an attempt to understand and optimize the process. Initial experiments were performed to determine the effect of interruptions to aeration on citric acid production. Unless the value of the Dissolved Oxygen Tension (DOT) of the culture fell below the DOT crit. (20% of saturation), no gross effect was observed. When the DOT value fell to zero, citric acid production ceased. Production however, recovered after recommencement of aeration, albeit after a delay. Experiments were performed in batch fermentation using various non-carbohydrate medium components as the growth-limiting nutrient. Nitrogen-, phosphate- or sulphate-limited cultures resulted in strong citric acid production. The most significant observation during these fermentations was that the maximum citric acid production rate occurred prior to the exhaustion of the limiting nutrient, i.e. when the organism was at a positive growth rate. Chemostat experiments were performed in order to determine the effect of the growth rate and the culture DOT on citric acid production. Maximum citric acid production rates and yields were achieved at low growth rate (u = 0.017 h-1 ) and high DOT (90% of saturation) values. The specific citric acid production rate was twice the maximum observed in batch fermentation, and the product yield was increased by 23%. The information regarding growth rate and DOT gained from the chemostat experiments was applied to a continuous fed-batch fermentation using nitrogen as the growth-limiting nutrient. The overall fermenter productivity attained was double that of the batch fermentation, resulting in a halving of the fermentation period. This is the first reported use of the continuous fed-batch technique for citric acid production. In all three fermentation modes (batch, chemostat and fed-batch), nitrogen limitation was superior to phosphate limitation in terms of citric acid production rates and yields. A double nitrogen/phosphate limitation gave results almost identical to a nitrogen limitation. The evidence suggests that the nitrogen nutrient exerts a form of catabolite repression on citric acid accumulation.