Search

In order to assess the numerical model for the prediction of the pump performance of a low specific speed centrifugal pump in cavitating flow conditions a numerical 3D analysis with a state-of-the-art CFD method and cavitation model by Zwart et al. [ 1 ] is performed for both, design and off-design conditions with varying surface roughness. Measured head and suction head data of in-house experiments with two different volute roughness levels are used to validate the unsteady simulation results. Regarding single-phase flow, significant differences to the measured head are observed assuming hydraulically smooth walls in the numerical model, in particular for over load. By employing a surface roughness model the simulation results show a decrease of the head at higher flow rates according to the measurements. Further deviations between simulation and measured data at over load are attributed to flow separation at the tongue of the volute, which is inaccurately resolved by the wall function approach. For cavitating flow conditions the influence of the surface roughness on the 3% suction head is minor. The trend of the measured NPSH 3% curve is qualitatively reproduced by the simulation. A steep rise of the NPSH 3% curve towards over load is attributed to cavitation at the volute tongue.

Toxoplasma gondii und Plasmodium Spezies sind obligat intrazelluläre Parasiten, die Zucker zur Energiehomöostase als auch für die Synthese lebenswichtiger Makromoleküle verwenden. Die hier vorgestellten Daten zeigen, dass der Glukosetransporter von T. gondii, TgGT1, und die homologen Transporter von P. falciparum und P. berghei, PfHT1 und PbHT1, neben Glukose auch Mannose, Fructose und Galactose transportieren. Toxoplasma Tachyzoiten exprimieren neben TgGT1 noch einen weiteren putative Zuckertransporter (TgST2) an der Parasitenoberfläche. Beide Proteine sind nicht essentiell, wie durch ihre individuelle und gleichzeitige Gendeletion belegt wird. Die Deletion von TgGT1 bewirkt einen geringen Wachstumsdefekt. Die Mutante ?tggt1 zeigt keine Glukoseaufnahmeaktivität und folglich eine verminderte glukoseabhängige Motilität. In ?tggt1 Parasiten wird ein verstärkter Glutaminstoffwechsel nachgewiesen, der ausreichend ist dessen Motilität und Replikationsaktivität zu erhalten. Die ?tggt1 Mutante gewährt Einblick in die Anpassungsfähigkeit von T. gondii an unterschiedliche Wirtszellen. Im Gegensatz zu T. gondii benötigen erythrozytäre Plasmodien Glukose und der Transporter PfHT1 wird derzeit als drug-target eingestuft. Hier wird gezeigt, dass das PfHT1-Homolog, PbHT1, essentiell in Blutstadien des Nagerparasiten Plasmodium berghei ist, jedoch auch während des gesamten Lebenszyklus des Parasiten exprimiert wird. Ein PfHT1- und PbHT1-spezifischer Inhibitor (Compound 3361) kann die Entwicklung von P. berghei Leberstadien und Okineten stark hemmen. Um zukünftig PfHT1-Inhibitoren im Hochdurchsatzverfahren zu identifizieren und testen zu können, wurden auf Saccharomyces cerevisiae und P. berghei basierende Expressionssysteme für PfHT1 entwickelt. Abschließend stellt diese Arbeit die Unterschiedlichkeit des zentralen Kohlenstoffwechsels von Toxoplasma und Plasmodium Parasiten durch bisher unbekannter Aspekte heraus. Toxoplasma gondii and Plasmodium species are obligate intracellular pathogens that utilize host sugars for energy homeostasis and macro molecular synthesis. Here, we report that the T. gondii glucose transporter, TgGT1, and of its homologs of P. falciparum and P. berghei (PfHT1 and PbHT1) transport glucose, mannose, galactose and fructose. Besides TgGT1, Toxoplasma harbours one additional surface localized putative sugar transporter (TgST2). Surprisingly both Proteins are nonessential and only the deletion of TgGT1 inflicts a mild defect in the parasite replication. The ?tggt1 mutant is unable to import glucose and consequently displays an attenuated glucose-dependent motility, which is completely rescued by glutamine. ?tggt1 performs increased glutamine metabolism that is sufficient to sustain motility and replication. The ?tggt1 strain provides a model for further investigating its adaptation to disparate host cells. In contrast to T. gondii, erythrocytic stages of Plasmodium species critically depend on glucose uptake, and the PfHT1 transporter is considered as a drug target against human malaria. Here, we report that PbHT1 (a PfHT1 homolog) is also essential for blood stage development in the rodent malaria parasite P. berghei. PbHT1 is expressed throughout the life cycle. Moreover, a PfHT1- and PbHT1-specific sugar analogue, compound 3361, can inhibit the hepatic development and ookinete formation in P. berghei. These results signify that PbHT1 and exogenous glucose are also required during the ex-erythrocytic stages of P. berghei. To permit a high-throughput screening of selective PfHT1 inhibitors and their subsequent in vivo assessment, we have established a PfHT1-expressing Saccharomyces cerevisiae mutant and generated a PfHT1-dependent ?pbht1 of P. berghei strain. This thesis underscores various previously unknown aspects of sugar metabolism in Toxoplasma and Plasmodium, and unravel their metabolic differences.