Doctor of Philosophy

Résumé

A Doctor of Philosophy (PhD, Ph.D., or DPhil; Latin: philosophiae doctor or doctor philosophiae) is the most common degree at the highest academic level, awarded following a course of study and research. PhDs are awarded for programs across the whole breadth of academic fields. Because it is an earned research degree, those studying for a PhD are required to produce original research that expands the boundaries of knowledge, normally in the form of a dissertation, and defend their work before a panel of other experts in the field. The completion of a PhD is typically required for employment as a university professor, researcher, or scientist in many fields. Individuals who have earned the Doctor of Philosophy degree use the title Doctor (often abbreviated "Dr" or "Dr."), although the etiquette associated with this usage may be subject to the professional ethics of the particular scholarly field, culture, or society. Those who teach at universities or work in academic, educational, or

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Influence of pH on dehalorespiring consortia & first steps in the development of a methodology for acid neutralization in enhanced in situ bioremediation

Nicole Munz

Enhanced in situ bioremediation of chlorinated solvents is, especially in source zone remediation, often limited through the accompanied high acidification of groundwater. This acid built-up originating from the dechlorination itself and fermentation products, such as organic acids, presents a draw-back in the efficiency of dehalorespiring bacteria. It is therefore indispensable to develop and implement appropriate buffering strategies to ensure a constant transformation of toxic chloroethenes to the final non-toxic product ethene. In this study pH tolerance of different dehalorespiring bacteria was tested. The limiting acidic pH varies significantly among the consortia. The consortium SL23b4 (PCE to ethene) grows at all the examined pH (pH 5 to pH 7.5) with a pH optimum between 6 and 7 (depending on the dechlorination step), whereas Maroc 6b (PCE to ethene) was only found to grow at incubation pH of 7, and very slowly at pH 6.5. The consortium 2SO (cis-DCE to ethene) seems to be inhibited at acidic pH (no growth at pH 5 and 5.5) having a pH optimum above neutral pH. In most cases incomplete dechlorination was observed in cultures growing at acidic pH or below the pH optima, accumulating toxic intermediate dechlorination products as a consequence. Additionally, high rates of dechlorination were always accompanied by pH drops up to 1.2 pH units, giving evidence of high acid production. pH had also influence on the community composition. In the consortium SL23b4 a shift from a Dehalococcoides- (pH 6-7.5) to a Sulfurospirillum spp.- (pH5 -5.5) dominated community was observed. Consortium Maroc 6b showed significantly different community compositions due to a pH change of only 0.5 pH units. Dehalococcoides spp. and Dehalobacter spp. were dominating at pH 7 and pH 6.5, respectively. Consortium 2SO is dominated by Dehalococcoides spp. at all pH, although at pH 7 a much higher diversity seems to prevail, with the threefold number of OTUs. Tests on the tolerance of the dehalorespiring consortia for elevated PCE concentration showed similar patterns for the different dechlorination steps, as for pH cultures, and confirmed a generally higher sensitivity towards PCE and pH changes for the last steps of dechlorination. Conclusively, Dehalococcoides spp., the only known genera able to perform complete dechlorination, seem to be highly sensitive to pH and PCE changes. Further, abiotic experiments on silicate mineral dissolution, using forsteritic olivine, were performed to simulate the buffer capacity of the minerals for the acid production during microbial reductive dechlorination. In these experiments, the buffer capacity was insufficient to counterbalance the constant acid titration rate, resulting in a final pH between 3 and 4 (initial pH of 7). The formation of precipitates, such as iron oxide, and the re-precipitation of magnesium were observed in some cases, showing a decrease in magnesium concentrations.

2010

Chargement

Role of Protein Kinase C and Munc18-1 in a Presynaptic Form of Plasticity, Post-tetanic Potentiation

Özgür Genç

Neurons are arranged in networks in which they communicate between each other by the means of synapses. Synaptic transmission can undergo activity-dependent and short-lived changes in strength, known as short-term synaptic plasticity. Short-term plasticity is an important mechanism for neural networks in living organisms, which plays a role in adaptation to sensory inputs and information processing. One of the interesting forms of short-term enhancement in transmitter release is post-tetanic potentiation (PTP). PTP is generated upon repetitive activity of the synapse and lasts tens of seconds to minutes. A more detailed understanding of the molecular mechanisms of short-term plasticity will be helpful to understand information processing in neural networks. Here, I studied the cellular and molecular basis of post-tetanic potentiation at the calyx of Held model synapse. Pharmacological inhibition of conventional protein kinase C (cPKC) isoforms resulted in a near- complete block of PTP. This showed that cPKC dependent phosphorylation of a target presynaptic protein is a key process underlying PTP. Upon inhibition of phosphatases by calyculin, PTP was remarkably prolonged, by the suppression of dephosphorylation. By expressing a FRET (Fluorescence Resonance Energy Transfer) based PKC activity probe, I obtained independent evidence for transient activation of cPKC during PTP. This refers to a transient phosphorylation/dephosphorylation, which underlies the short-term changes in the release probability during PTP. To investigate the target protein, which becomes phosphorylated by PKC during PTP, I studied phosphorylation of the presynaptic protein Munc18-1. By establishing a virus-mediated in vivo gene-replacement approach using floxed Munc18-1 mice, we replaced endogenous Munc18-1 with phosphorylation-deficient form of Munc18-1. I showed that in the nerve terminals expressing the phosphorylation deficient form of Munc18-1, PTP was strongly suppressed as compared to the wild type form of Munc18-1. This PhD thesis work proposes a molecular model for PTP in which a transient phosphorylation/dephosphorylation of Munc18-1 by conventional PKCs and phosphatases, respectively modulates the calcium sensitivity of vesicle fusion and determines the kinetics of PTP.

EPFL2013

Chargement

Microalgae are small organisms that live in water and use solar energy or artificial light to grow. They are emerging to be one of the most promising long-term, sustainable sources of biomass for fuel, food, feed, and other high valuable co-products. Like any other plant, algae, when grown using sunlight consume carbon dioxide (CO2) and release oxygen (O2), but with a 5 to 10 times faster growth rate than conventional food crops. Thus, algae-based CO2 conversion is considered as a cost-effective option for CO2 capture and the mitigation of greenhouse gas emissions (GHG). Since the last decade, there have been repeated attempts to bring microalgae bioenergy and biomaterial production to an industrial level. So far, despite the enthusiastic boost towards commercialisation, the production of microalgae has been demonstrated mainly at pilot scale levels, and only a few large-scale facilities exist and produce microalgae today. There are several issues related to microalgae cultivation from either the energetic, environmental or economical point of view. Further developments are needed for algal biomass technologies to improve their cost-competitiveness and their environmental sustainability. The major bottlenecks are mainly linked to water and nutrient supply, the high energy consumption of algal processing, the high surface area requirements for cultures, and finally, the relatively low solar conversion efficiency of microalgae in highly sunny regions. Therefore, to design economically feasible algae production processes, it is necessary to close the nutrient cycle, to reach the energy balance, and to opt for a biorefinery concept where products can be valorised. This doctoral thesis aims to explore a new concept, PAWaSto, which attempts to overcome the limitations of microalgae production processes by combining different technologies to increase the energy and nutrient recoveries within the system. An urban environment was considered in the PAWaSto vision. This work focuses on four different research approaches which can be summarised as follows: (1) As low-cost water and nutrient supply source is critical to the success of microalgae production, a unique on-site sanitation system for nutrient and water recoveries (household effluents) was studied in this thesis. (2) Energy and nutrient recycling: The integration of a hydrothermal process (HT) for a fast conversion of household effluents to concentrated nutrient-rich effluents, free of pathogens, suitable for algae production was proposed. Besides, the produced energy-rich gas obtained from the HT is considered for electricity generation through a solid oxide fuel cell (SOFC). (3) The implementation of semi-transparent dye sensitised solar systems (DSCs) on the illuminated surface of an algae photobioreactor, and their effect on the algal biomass productivity was studied for the first time in this thesis. (4) Finally, for the economic viability of algal biomass production, the extraction of high-value products from wet algal biomass using green solvent was proposed, and the residual biomass generated from the extraction step was further treated through a HT process. Overall this doctoral research project studied key aspects for the integration of a biorefinery concept in urban areas contributing to the big vision of closing the materials cycles on the level of districts. A focus was put on an integrated system for efficient microalgae production, power generation, and closing the nutrient cycle.

EPFL2020

Chargement

Role of Protein Kinase C and Munc18-1 in a Presynaptic Form of Plasticity, Post-tetanic Potentiation

Özgür Genç

EPFL2013

Influence of pH on dehalorespiring consortia & first steps in the development of a methodology for acid neutralization in enhanced in situ bioremediation

Nicole Munz

2010

EPFL2020