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Coming dissertations at Uppsala university

  • Adapting to succeed : Post-transcriptional gene regulation in Salmonella Author: Alisa Rizvanovic Link: Publication date: 2022-05-18 10:28

    Salmonella are zoonotic pathogens of worldwide economic and health importance. Both during life outside and inside the host, these pathogens are subject to continuously changing environmental conditions, such as temperature changes, acid stress, nutrient limitations, and others. In order to thrive and survive, Salmonella must respond to these changes by adapting their physiology and morphology through changes in gene expression. RNA-binding proteins (RBPs) often work in concert with small RNAs (sRNAs) to control gene expression at the post-transcriptional level. Their mode of action includes regulation of RNA translation and/or stability, either positive or negative. Recently, ProQ was discovered to be a global RBP with a large repertoire of mRNA and sRNA targets in Salmonella. However, many details regarding ProQ biology are not fully understood, including the requirements for RNA-binding, mechanisms of gene regulation, and ProQ-dependent phenotypic changes. The main purpose of this doctoral thesis was to characterize the RBP ProQ and its regulatory role in Salmonella.

    First, we developed a method based on saturation mutagenesis coupled to phenotypic sorting and high-throughput sequencing to chart the functionally important regions in ProQ. Our results reveal that both the N-terminal and C-terminal domains are important for ProQ’s gene regulatory function, but the underlying mechanisms differ. Second, we show that ProQ is important for flagellar-mediated motility in Salmonella. More specifically, we show that ProQ and an associated sRNA promotes flagellar gene expression and motility by affecting translation of the master flagellar regulator FlhDC. Finally, we reveal that ProQ induces persister formation in Salmonella and enables a subpopulation of cells to survive high doses of different types of antibiotics through growth arrest.

    In conclusion, the findings presented herein provide new insights into the role of ProQ as a global post-transcriptional regulator of gene expression in Salmonella. Together, these findings contribute to our understanding of how Salmonella shapes its lifestyle and induces pathogenesis.  

  • “Closed Place, Open Word” : Reading the Postplantation in Earl Lovelace, Milton Murayama, and Ntozake Shange Author: Sally Anderson Boström Link: Publication date: 2022-05-18 09:51

    This dissertation focuses on three authors who came of age in the 1980s, Earl Lovelace, Milton Murayama, and Ntozake Shange, reading their novels set respectively on Trinidad, Hawai‘i, and the Sea Islands, as postplantation expressions. My definition of the postplantation builds upon the work of Édouard Glissant, especially “Closed Place, Open Word” where he delineates three phases in literary production from the Plantation: the first is chiefly oral and appears as an “act of survival,” the second is an attempt to justify the Plantation system and is marked by “delusion,” and the third phase is written by descendants of the Plantation in a “passion of memory.” It is this third phase that I call the postplantation. Here, several generations after the system’s collapse, writers return to the plantation as a way to process its legacy. An integral part of this process for the authors studied here is the use of Creole languages developed on the plantation and still spoken today. This dissertation’s specific contribution is to show how the history of the plantation is central to contemporary island discourse. My comparative study of novels about Trinidad, Hawai‘i, and the Sea Islands untangles the effect of the plantation in each of these locations: the legacies of racial and sexual trauma, poverty, and the power structures that continue to replicate the plantation, but also the culture and language that emerged in triumph from this dehumanizing system. My readings of the postplantation illustrate how despite writing about three seemingly very different locales, Lovelace, Murayama, and Shange are engaged in similar efforts to reclaim a local culture, language, and history denied in the plantation’s violent trajectory. The emerging field of island studies, archipelagic approaches to literature, and studies of vernacular in world literature speak to the significance of this doctoral study. 

  • Electrostatic plasma waves associated with collisionless magnetic reconnection : Spacecraft observations Author: Konrad Steinvall Link: Publication date: 2022-05-18 09:24

    Magnetic reconnection is a fundamental plasma process where changes in magnetic field topology result in explosive energy conversion, plasma mixing, heating, and energization. In geospace, magnetic reconnection couples the Earth’s magnetosphere to the solar wind plasma, enabling plasma transport across the magnetopause. On the sun, reconnection is responsible for coronal mass ejections and flares, which can affect everyday life on Earth, and it influences the evolution of the solar wind. Although collisionless magnetic reconnection has been studied for a long time, some fundamental aspects of the process remain to be understood. One such aspect is if/how plasma waves affect the process. Simulations and spacecraft observations of magnetic reconnection have shown that plasma waves are ubiquitous during reconnection. Particularly interesting are simulation results which show that electrostatic waves can affect the rate at which reconnection occurs, but this has not yet been experimentally verified. The recently launched Magnetospheric Multiscale (MMS) mission was designed to investigate the smallest scales of collisionless magnetic reconnection, making it an excellent mission to study small-scale waves as well. In this thesis, we use MMS to study electrostatic waves associated with magnetic reconnection in geospace. Our first two studies are devoted to the properties of electron holes (EHs), believed to play an important role in collisionless reconnection. Using MMS, we analyze EHs in unprecedented detail, and compare their properties to theory and previous studies. Importantly, we find evidence of EHs radiating whistler waves in the reconnection separatrices, a process which might modulate the reconnection rate. In our third study, we show that the presence of cold ions at the reconnecting magnetopause can lead to the growth of the ion-acoustic instability. This instability leads to dissipation and cold ion heating. The fourth study compares different techniques for determining the velocity of electrostatic waves. Accurate velocity estimates are important, since they are needed to understand how the wave interacts with the plasma. Finally, in our fifth study, we calibrate the E-field measurements made in the solar wind by the Solar Orbiter spacecraft, to aid future studies of solar wind processes, including magnetic reconnection.