Department of Biochemistry, Microbiology and Biotechnology
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Item The reactions of ozone with compounds relevant to drinking-water processing: Phenol and its derivatives(University of Namibia, 2002) Mvula, Eino N.Kinetic and mechanistic investigations on the reactions of ozone with phenol and some of its derivatives (hydroquinone, catechol, phloroglucinol, pentachlorophenol, pentabromophenol, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene and 1,3,5-trimethoxybenzene) have been carried out. These compounds were chosen, as they can serve as models for compounds which are abundant in surface waters and wastewater. The scope of the investigation was widened by including dihydrogen sulfide, often a contaminant of ground waters in arid areas, and its organic analogues. By employing various analytical techniques, such as high performance liquid chromatography (HPLC); ion chromatography (IC); nuclear magnetic resonance spectroscopy (NMR); gas chromatography (GC) and gas chromatography coupled to mass spectroscopy (GC-MS), it was possible to identify and quantify reaction products. The stopped-flow technique was employed to measure rate constants of ozone reactions. When strong substrate absorptions at 240–280 nm prevented the use of this technique, rate constants were measured by competition kinetics. Pulse radiolysis was used for the study of OH-induced reactions. Methods were developed for the detection and quantification of reactive intermediates in ozone reactions such as singlet dioxygen, OH, O2 and hydroperoxides. A germanium diode detector was used for the quantification of O2(1g) formation. For the detection of OH formation, 2-methyl-2-propanol and DMSO were used and tetranitromethane was applied for the detection of O2. Based on the products in the reactions of ozone with phenol and its derivatives, various reaction pathways have been identified. Ozone reacts with phenol and its derivatives by ozone addition (Criegee mechanism), electron transfer and O-atom transfer reactions. The Criegee mechanism, practically the only reaction with olefins, often occurs to only a small extent here. Instead, OH (up to 26%), O2 and O2(1g) are major intermediates. The occurrence of the Criegee mechanism was confirmed by the yields of hydrogen peroxide and their corresponding carbonyl compounds. The Criegee mechanism is shown to be more pronounced in methoxybenzenes as compared to phenols. For example, in the reaction of ozone with 1,4-dimethoxybenzene, the hydrogen peroxide yield (56%) and that of methyl(2Z,4E)-4-methoxy-6-oxo-hexa-2,4-dienoate (52%), which are the products of the Criegee type reaction, are much higher than that of hydrogen peroxide (5.6%) in the reaction of ozone with hydroquinone. A possible reason for this is that, i.e. the zwitterion formed in the reaction of ozone with hydroquinone may undergo a deprotonation reaction [reaction (1)] which competes with the 1,3- dipolar cyloaddition [reaction (2)] whereas in the case of the zwitterion formed in the reaction of ozone with 1,4-dimethoxybenzene, the 1,3-dipolar cycloaddition may occur without hindrance.Item Optimization conditions for the production of Arachidonic acid by the microalga Parietochloris Incisa under indoors and outdoors conditions(University of Namibia, 2005) Shuuluka, DiinaThe freshwater green microalga Parietochloris incisa is the richest known plant source of the polyunsaturated fatty acid (PUFA), arachidonic acid (20:4ω6, AA). Accumulation of AA and docosahexaenoic acid (22:0, DHA) is necessary for brain and retina development in infants. While many microalgae accumulate triacylglycerols (TAG) in the stationary phase or under certain stress conditions, these TAG are generally made of saturated and monounsaturated fatty acids. In contrast, most cellular AA of P. incisa resides in TAG. This is of practical value, since TAGs are the preferred chemicals to introduce AA into baby formulae. Studies using different cultures conditions were carried out to assess their effects on AA production. Under different cell densities, low, medium and high (LD, MD and HD, respectively), the cells of P. incisa showed a different pattern of chlorophyll content. At LD, cells followed the process of nitrogen starvation, decrease in chlorophyll content, accumulation of carotenoids and showed signs of bleaching at the end of cultivation period. In the same way, cells grown at MD followed the same pattern though it was not more pronounced compared to the former. However, at HD, cells continued to increase the chlorophyll content, probably by continuing to build the photosynthetic membranes to maximize light harvesting. The AA content increased in all cultures irrespective of the initial cell density. Volumetric biomass accumulation was higher in HD cultures, eventually the volumetric AA yield was also higher. The growth stage at which cultures were transferred to N-free medium had a pronounced effect on chlorophyll synthesis of P. incisa. The rate of chlorophyll synthesis was faster in cultures transferred in EXP (exponential) and TRANS (transition) phases. Similarly, the biomass accumulation was rapid in cultures transferred in the EXP and TRANS phases. The proportion of AA of total fatty acid increased faster in cultures transferred to N- starvation in the EXP and TRANS phases of growth. The proportion of AA almost doubled from 25.8% to 47.5% and from 25.8% to 49.8% of TFA, respectively at day 14. Cultures transferred in the E.STA (early stationary) and M.STA (middle stationary) phases of growth, had higher initial proportion of AA, amounting to 34.9% and 36.3%, respectively, at day 0. Their proportion of AA had increased slowly throughout the cultivation period, reaching 47.3% and 47.0% at the end of cultivation period. Cultures growing on complete medium and supplemented with fatty acid precursors were able to incorporate and further modify both incorporated oleic acid and linoleic acid to AA. This was evident only with 3d cultures at the EXP stage. Older cultures did not demonstrate an enhancement in AA production, but rather a reduction. Supplementation of N-starved cultures did not enhance AA production. Increasing the C/N ratio favors lipid accumulation in microalgae by inducing de novo lipid synthesis. Indeed, high CO2 significantly enhanced the TFA synthesis in P. incisa indicating that under enriched CO2 conditions the rate of de novo synthesis of fatty acid is higher. However, this phenomenon was only evident up to 10 days. Cultivation of P. incisa on BG11-N with high CO2 did not favor an increase in the proportion of AA, moreover, the proportion of 18:1 increased at the expense of AA. This might indicate either an inhibition of sequential desaturation or favored synthesis of shorter and less desaturated fatty acids. Increasing the CO2 level in HD cultures on BG11-N and tap water media did not cause any significant changes in the TFA and AA contents. In developing a large-scale cultivation for AA, it is necessary to utilize inexpensive medium component to lower the cost. Tap water and brackish water were used to induce starvation in P. incisa in HD cultures. Cells of P. incisa survived in tap water, which basically contains no nutrients for sustaining growth. More diluted cultures were not able to survive under those conditions. It is therefore clear that growing cells of P. incisa under HD can allow the cells to grow under nutrient-devoid medium. Cells of P. incisa were able to produce biomass rich in arachidonic acid on tap or brackish water. Not only is this media less expensive but also it saves labor in media preparation, reducing the final cost of the product. By growing P. incisa under outdoors conditions, this study represented an ideal approach to making the realization of commercial production of AA possible. The volumetric productivity of AA and TFA, as well as the daily accumulation of AA were almost the same in outdoors and indoors cultures at day 8. On subsequent days, indoors culture attained higher productivities, probably such differences was due to contaminations that were microscopically observed in outdoors cultures at day 9Item Evaluation of the quality characteristics of the Marama bean (Tylosema esculentum), an underutilized grain and tuber producing legume in Southern Africa(University of Namibia, 2005) Müseler, DLThe potential of the marama bean plant, Tylosema esculentum (Burch.) Schreiber, a drought-tolerant, bean–bearing legume, native to Southern Africa, was investigated to potentially form part of a food based approach in rural agricultural extension programmes. Nutrient content and sensory attributes of roasted marama beans were determined as well as the potential of the marama plant as fodder for cattle. Chemical analyses were performed on roasted Namibia and Botswana marama beans to determine the nutritional content thereof. The beans contain high levels of protein, unsaturated fats, phosphorus, calcium, vitamin A, vitamin B3, vitamin B6, folic acid, vitamin B12, vitamin E, iron, zinc and iodine. Quantitative descriptive sensory analyses were performed on roasted marama beans from Botswana and Namibia to determine and compare the sensory attributes thereof. The Botswana traditionally roasted, Botswana oven roasted and Namibian oven roasted samples grouped together. The Namibian traditionally roasted marama bean had a significantly more intense burnt, bitter and chemical aroma and flavour and taste. To assess the value of the marama plant as a fodder for cattle, an experiment was conducted to measure the effect of season, stocking rate and frame size on the diet selection of the marama plant by cattle grazing the veld of the Sandveld Research Farm in the eastern part of Namibia. This study proved that only season had a significant influence on the selection of the marama plant as a feedstuff for cattle. The marama plant is indeed utilized by free-ranging beef cattle, but not preferentially so.Item Conservation attitudes and patterns of biodiversity loss in the Ohangwena and Oshikoto regions of Namibia(2006) Henghali, Josephine N.Item Factors affecting initial seedling establishment of hoodia gordonii in !Khob !Naub conservancy, Namibia, Africa(2007) Lisao, Melvin M.Abstract provided by authorItem Habitat suitability and recommendation for the reintroduction of the European pond Turtle Emys Orbicularis (Lininnaeus 1975) to the area of community interest "Locknitztal" in Brandenburg (Germany)(University of Namibia, 2007) Merz, KathleenThe European pond turtle (Emys orbicularis) is one of the most endangered vertebrate species in Germany. The species conservation programme “Europäische Sumpfschildkröte”, which was initiated in 1993 / 94, deals with the exploration of biology and the protection of the few still existing small populations. For the protection of the species, reintroduction to its former range is taken into consideration. The present study evaluates the habitat suitability of the nature reserve and FFHb (Flora-Fauna Habitat) area “Löcknitztal” (Brandenburg) for Emys orbicularis. The study area is characterised by natural and remote appearance, high conservation status, high public interest in Emys orbicularis promoted by the “Freundeskreis Wappentier” (Supporters of the Emblem Animal) and a great voluntary engagement for the maintenance of the conservation area by the “Interessengemeinschaft Löcknitztal” (Löcknitztal Community of Interest). Historical sources were reviewed to reconstruct the historical development of the study area and to identify when and where important changes in landscape structures occurred. The present biotope structures were analysed using data sheets which were developed with special focus on habitat requirements of Emys orbicularis. The biotope structure analysis comprised a review of terrestrial habitats and aquatic habitats. The assessment was conducted from land, water and air. Furthermore, diet availability and predator pressure were estimated. The research determined that suitable aquatic and terrestrial structures are still present in the northeastern part of the study area. The analysis of potential food items proved sufficient availability of prey species. The high predator pressure could have a negative impact on the reintroduction. To maintain the suitability of the area for Emys orbiclaris, habitat management is required. It should be realised in cooperation with the IG – Löcknitztal and the sheep company Kölpin - Fritsche active in the valley. These conservation measures would not only support the turtle population but also contribute to the maintenance and increase of biodiversity in the conservation area.Item Microbial ecology of anaerobic carbon mineralization in Namibian shelf sediments(2007) Julies, Elsabe M.This PhD thesis is an essential component of the 'Namibia Gas' (NAMIBGAS) project, which aims to improve the understanding of the rate and fluxes of hydrogen sulfide and methane to the sediment surface and into the water column on the Namibian shelf, which is one of the most productive upwelling systems on Earth. Organic matter degradation in the sediment drives hydrogen sulfide production, the maintenance of anoxia, and methane formation. Therefore, the primary aims of the thesis are to study carbon transformation processes within the sediment, determine the reactivity of organic carbon in the sediment and, investigate the control of microbial community structure and activity by the amount and accessibility of carbon sources. The emphasis is on linking microbial community structure (identity) to their function (activity) to provide new insights into the microbial ecology that controls carbon turnover in these upwelling sediments. By studying the stepwise degradation of organic carbon a complete process overview of organic carbon mineralization could be obtained.Firstly, the diagenetic transformation of dissolved organic carbon (DOC), in particular dissolved carbohydrates, was studied by using both biogeochemical methods and molecular techniques. The bulk sediment composition, pore water chemistry, polysaccharide hydrolysis rates, 35S-sulfate reduction rates, and the abundance of active bacteria involved in the initial and terminal processes of organic carbon degradation within the top 15 cm of the sediment from two sampling stations were determined (Chapter 2). Secondly, the diversity of bacteria from the same two sampling stations within the top 12 cm of the sediment, using the 16S rRNA library approach were investigated (Chapter 3). The central question was whether shifts of the community structure of bacteria involved in the major carbon transformation steps of hydrolysis, fermentation, and terminal oxidation are reflected in changes of biogeochemical rates. Finally, the effect of a sudden high input of DOC into the sediment in the form of high molecular weight substances (the polysaccharide laminarin) and low molecular weight substances (lactate and acetate) on the metabolic activity and community structure of bacteria involved in initial hydrolytic and fermentation steps and terminal oxidation was investigated during two separate experiments (Chapter 4). Substrate addition simulates the high input of organic matter into the sediment after a phytoplankton bloom, following upwelling events.Item Genetic diversity of sorghum (sorghum bicolor (l.) moench) and its wild relatives in Namibia using ssr and rapd analyses(2007) Nghishikungu-Horn, Lydia N.Abstract provided by authorItem Seasonal occurrence of fleas and other ectoparasites on small mammals at Waterberg Plateau, Namibia(2007) Uusiku, Saara S.Abstract provided by authorItem The distribution, abundance and reproductive status of the invasive alien plant, Datura Innoxia Mill., in the city of Windhoek, Namibia(2008) Katjirua, JoyceAbstract provided by authorItem Multi-scale assessment of habitat use by Black Rhinos (Diceros bicornis Linnaeus 1758) in North West Namibia(2008) Shivute, Basilia A.;Abstract provided by authorItem The impacts of different fire frequencies on vegetation characteristics in the Hamoye state forest, Kavango region, Namibia(2008) Shoopala, RabanusAbstract provided by authorItem Sustainable management of Harpagophytum procumbens and the effect of effective micro-organisms and sulphuric acid on its seed germination(2008) Mowa, EdgarAbstract provided by authorItem Effects of environmental variability on fish diversity and composition along the Southern Namibian Coastline during summer(2009) Nashima, Festus P.Abstract provided by authorItem The Synthesis and characterization of copper(II) complexes containing thiosemicarbazone and semicarbazone ligands derived from Ferrocene and pyridyl fragments(2009) Likius, Daniel S.Abstract provided by authorItem Seed production, viability and germination of Citrullus Lanatus at the King Nehale conservancy(2009) Kaura, UazamoAbstract provided by author