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    Impact of Anthropogenic and Natural Disturbances on Biodiversity Patterns of Macroinvertebrates at different Taxonomic Levels in African Freshwater Systems
    (2025) Dusabe, Marie Claire
    African freshwater ecosystems are subject to both natural and anthropogenic pressures that affect habitat quality, biodiversity, and ecosystem functioning. Macroinvertebrates have been used in routine bioassessments to detect disturbances for decades. However, it is unclear how accurately they reflect disturbances at different taxonomic levels. This thesis investigates the environmental impact of disturbances in selected East African freshwater ecosystems, and how macroinvertebrates respond to these changes at different temporal and spatial scales. The effects of dam construction and the effectiveness of family-level bioindication for detecting them were tested on the Ruzizi River. Multimetric indices (MMIs) were used in Lake Kivu to assess their ability to identify and distinguish between various environmental pressures. Mollusc community indices were used to assess long-term environmental changes in six Albertine volcanic lakes. Additionally, the freshwater snail Gabbiella was tested as a model taxon to reconstruct historical hydrological shifts and water level fluctuations across the African Great Lakes, major connected river systems, and the crater lakes of western Uganda based on phylogenetic and biogeographical analyses. Finally, an eDNA index was used at Lake Albert to test its applicability in biodiversity surveys and use in African freshwater biomonitoring systems. The results showed that on the Ruzizi River, family-level indi-cators did not adequately capture the impact of the dams, while on Lake Kivu multimetric indices more effectively distinguished between stressed and reference sites. Pollution patterns varied across the lake, with greater impacts in the northern basin than in the central and southern basins. Phylogenetic and biogeography indices proved useful in detecting historical disturbances. The diversification of Gabbiella mirrored earlier water-level changes, a trend also reported in other African molluscs and fish groups. A series of vicariance and dispersal events shaped the biogeographic history of Gabbiella humerosa, and allowed tracing historical drainage changes during the Pleistocene. However, eDNA analysis yielded limited records of macroinvertebrates, as plankton dominated because only surface water was sampled. The lack of a reference library makes it difficult to accurately assign eDNA sequences. Nevertheless, the results underscore the potential of using aquatic eDNA for taxonomy-free biomonitoring in tropical regions. The results of the historical molluscan biodiversity change in the six volcanic barrier lakes studied in this thesis show that new species have emerged and others have disappeared over time. Invasive taxa were common, with crayfish and non-native snails among those displacing native species. The biogeography of most Albertine volcanic barrier lakes exhibits a Nilotic affinity, except for invasive species and other taxa with wide distributions. The current findings provide a useful basis for conservation efforts and inform strategies to slow the ongoing loss of biodiversity.
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    Medic responses to water deficit alone or combined to salinity, evaluation of their yield and priming effects
    (2025) Gharred, Jihed
    This thesis investigates the responses of two forage species, M. ciliaris and M. polymorpha, to water deficit, both alone and in combination with salinity. Additionally, it explores strategies to enhance their productivity under these challenging conditions, focusing on approaches such as seed priming and the incorporation of biochar into the culture medium. In Medicago ciliaris, drought (36% water holding capacity) led to a significant reduction in plant growth and an increase in the root/shoot ratio. The growth response was accompanied by a decreased stomatal conductance and a reduction of the net CO2 assimilation rate and water use efficiency. The associated higher risk of ROS production was indicated by a high level of lipid peroxidation, high antioxidant activities, and high proline accumulation. Soil amendment with biochar (2%) enhanced the growth significantly and supported the photosynthetic apparatus of Medicago ciliaris species by boosting chlorophyll content and Anet both under well-watered and insufficiently watered plants and water use efficiency in case of water shortage. This increase in water use efficiency was correlated with the biochar-mediated decrease of the MDA and proline contents in the leaves, buffering the impact of drought on photosynthetic apparatus by increasing the activity of enzymatic antioxidants SOD, APX, GPOX, and GR and non-enzymatic antioxidants, such as AsA and DHAsA, giving the overall picture of a moderate stress response. These results confirmed the hypothesis that biochar application significantly reduces both the degree of stress and the negative impact of oxidative stress on Medicago ciliaris plants. These results implied that this species could be suitable as a cash pasture plant in the development of agriculture on dry wasteland in a future world of water shortages. This study aimed to evaluate the extent to which seed priming with ascorbic acid (0.2 mM) enhances the performance of M. polymorpha L. under osmotic stress induced by 50 mM NaCl (salinity) or 100 g/L PEG. Parameters related to growth and photosynthesis were assessed to understand the impact. Both NaCl-induced salinity and PEG-mediated osmotic stress significantly reduced plant biomass (-30% and -40%, respectively), leaf and ramification numbers, stem length, net CO₂ assimilation, and leaf water content. However, both treatments, particularly PEG, increased the root/shoot ratio and leaf proline content. Interestingly, seed priming with ascorbic acid alleviated these stress-induced effects, improving CO2/H2O gas-exchange and increasing plant biomass production. Water relations also improved, as indicated by reduced leaf osmotic potential, enhanced proline accumulation, and higher leaf water content. Additionally, ascorbic acid seed priming increased leaf carotenoid content by 65% and chlorophyll content by 45%, thereby enhancing photosynthetic activity. These improvements collectively contributed to better plant performance, particularly under salinity stress. Seed priming with ascorbic acid is an easy, cost-effective, and promising approach to mitigate the impact of osmotic stresses like drought and salinity, especially by improving plant water relations and photosynthetic efficiency. The effects of salinity, soil drying, and their interaction on the two forage species Medicago ciliaris and M. polymorpha were investigated. The results revealed that salinity and drought applied individually adversely affected growth, photosynthesis, and leaf water and potassium content in both species. However, the combined effects of both constraints were not significantly additive. Salinity affected the growth of both species to a similar extent. The major advantage of M. ciliaris under dry or saline conditions seems to be its higher water use efficiency and its corresponding positive impact on the ROS risk. Compared to M. polymorpha, M. ciliaris demonstrated superior biomass production under drought, salinity, and combined stresses, making it a strong candidate for forage production and soil rehabilitation in arid and semi-arid salinized regions.
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    N-Glycanase-1-Mangel – Charakterisierung von Genvarianten
    (2025) Orczyk, Ralph Rene
    N-Glycanase-1-Mangel ist eine kongenitale Störung der Deglykosylierung. Die Krankheit ist durch fünf Kernsymptome geprägt: globale Entwicklungsverzögerung, Choreoathetose, Erhöhung von Leberwerten in Blutuntersuchungen, Hypo-/Alakrimie und eine progressive, sensomotorische Neuropathie. Der Erkrankung liegen Mutationen im Enzym N-Glycanase-1 (NGLY1) zu Grunde. Die N-Glycanase-1 ist vor allem an der ER-assoziierten Degradation von Proteinen beteiligt. Dabei werden N-Glykane vor der proteasomalen Degradation entfernt. Daneben interagiert es unter anderem mit NRF1/NFE2L1 und hat einen Einfluss auf unterschiedliche Signalwege. Bisher sind etwa 56 Mutationen bekannt, die zu der Erkrankung führen. Die Konsequenz jener Mutationen ist ein verminderter Spiegel von N-Glycanase-1 und somit eine verminderte Enzymaktivität. Der genaue Pathomechanismus ist jedoch Gegenstand aktueller Forschung und noch nicht abschließend geklärt. Mögliche Ansätze beziehen sich unter anderem auf eine Verminderung des oben genannten NRF1/NFE2L1 als Transkriptionsfaktor für proteasomale Gene. Diese Arbeit hatte das Ziel, die zwei NGLY1-Varianten, R390Q und R401*, des N-Glycanase-1-Mangels zu charakterisieren. Dafür wurde zunächst eine NGLY1-KO-Zelllinie generiert. Mit dieser wurde dann das Expressionsverhalten der Genvarianten nach transienter Transfektion untersucht. Die Expression von R390Q konnte mit den verwendeten NGLY1-Antikörpern nachgewiesen werden, während dieser Nachweis bei R401* ausblieb. Im Weiteren sollte ein Aktivitätsassay zur Bestimmung der Enzymaktivität von NGLY1 bzw. dessen Genvarianten etabliert werden. Hierzu wurde ein Venuskonstrukt, genannt ddVenus, verwendet, das erst nach Deglykosylierung durch NGLY1 fluoresziert. Damit konnte ein Rückschluss aus der Fluoreszenz auf die NGLY1-Enzymaktivität gezogen werden. Die Ergebnisse zeigten, dass die Enzymaktivität bei beiden Genvarianten hoch signifikant vermindert war. In weiteren Versuchen konnte die Aktivität von R390Q mit Betain nicht gesteigert werden, während bei R401* und der Verwendung von 50 μM Amlexanox mit einer Inkubationszeit von 48 Stunden eine Aktivitätssteigerung festgestellt werden konnte, die jedoch nicht signifikant war. Darüber hinaus wurde aufgezeigt, dass NRF1/NFE2L1 in den KO-Zellen in prozessierter Form akkumuliert. Eine Kompensation durch transiente Transfektion von NGLY1 oder der Genvarianten R390Q oder R401* konnte nicht erreicht werden.
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    Media Frames of Climate Justice in China
    (2025) Cheng, Yan
    This study examines how Chinese newspapers frame climate justice. It asks what media frames appear, how media outlets differ, and what social and political implications emerge. Using a multidisciplinary framework and critical discourse analysis, the study finds that Chinese media mainly reflect elite discourses, stressing climate diplomacy, distributive justice, historical responsibility, per capita emissions, and the right to development. China insists on these principles while cooperating internationally, especially on technology transfer and carbon intensity reductions. Energy security is central to its position, shaped by cultural and historical factors. China’s global identity remains ambiguous, shifting between developing nation and responsible major power. While frames are similar, market-oriented media take more bottom-up views. The study calls for a cosmopolitan approach, highlighting individual agency and the media’s potential to advance climate justice discourse.
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    Genetically-encoded fluorescent ATP sensors for mode of action analyses of antiparasitic compounds in Plasmodium falciparum
    (2025) Springer, Eric
    This dissertation is based on publications that have established the usage of novel methods for adenosine triphosphate (ATP) and pH determinations in Plasmodium falciparum (P. falciparum). Based on these and complementary methods, mode of action (MoA) analyses of established drugs and novel antiparasitic compounds were conducted to support drug development. The deadliest form of malaria, malaria tropica, caused by the intracellular parasite P. falciparum, claims more than half a million casualties annually. With resistances against each established antimalarial drug class against P. falciparum found in the field, the development of novel and improved antiparasitic compounds poses a matter of highest concern for global health. To this end, understanding of the underlying mechanisms is crucial. Therefore, within the scope of this work, genetically-encoded fluorescence-based ATP and pH sensors were stably integrated into the genome of P. falciparum. Within the adult blood stages of the parasite, this allowed an analysis of its energy metabolism, which is central for parasite survival. Based on this system, MoA analyses of a panel of antiparasitic compounds were carried out. In the case of a promising drug candidate, these were complemented with additional methods for elucidation of its mechanism. Thereby, two different variants of ATP sensors, ATeam1.03nD/nA and ATeam1.03YEMK, as well as an improved pH sensor, sfpHluorin, were established and characterized via plate reader spectrofluorometry and epifluorescence microscopy, for the first time in P. falciparum. In vitro and in cellulo characterization of the sensors demonstrated their proof of principle and unveiled advantages of the ATeam1.03YEMK sensor cell line in respect to fluorescence intensity and pH stability. Based on that, the effects of a selection of antiparasitic compounds on the sensor readouts were determined. This revealed characteristic response patterns caused by 4-aminoquinolines, arylamino alcohols, redox cyclers, as well as dihydroartemisinin, doxycycline, atovaquone, and cycloheximide. In a next step, the effects of the drug candidate arylmethylamino steroid compound 1o (1o) on the sensor readouts were determined. The investigation uncovered parallels to arylamino alcohols such as mefloquine. Based on these parallels, subsequent analyses via transmission electron microscopy (TEM), the parasitederived heme species distribution, as well as light microscopic morphology of stage-specific 1o incubations suggest that the parasite-killing activity could be based on interference with the parasite’s hemoglobin uptake. The results of this work benefit the understanding of P. falciparum’s parasite biology and the MoA of antiparasitic compounds to support drug development. Furthermore, the established system is now available for the malaria community to address a broad range of research questions.