@phdthesis{Maistrenko2021,
  author    = {Maistrenko, Oleksandr},
  title     = {Pangenome analysis of bacteria and its application in metagenomics},
  doi       = {10.25972/OPUS-21499},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214996},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {The biosphere harbors a large quantity and diversity of microbial organisms that can thrive in all environments. Estimates of the total number of microbial species reach up to 1012, of which less than 15,000 have been characterized to date. It has been challenging to delineate phenotypically, evolutionary and ecologically meaningful lineages such as for example, species, subspecies and strains. Even within recognized species, gene content can vary considerably between sublineages (for example strains), a problem that can be addressed by analyzing pangenomes, defined as the non-redundant set of genes within a phylogenetic clade, as evolutionary units. Species considered to be ecologically and evolutionary coherent units, however to date it is still not fully understood what are primary habitats and ecological niches of many prokaryotic species and how environmental preferences drive their genomic diversity. Majority of comparative genomics studies focused on a single prokaryotic species in context of clinical relevance and ecology. With accumulation of sequencing data due to genomics and metagenomics, it is now possible to investigate trends across many species, which will facilitate understanding of pangenome evolution, species and subspecies delineation. The major aims of this thesis were 1) to annotate habitat preferences of prokaryotic species and strains; 2) investigate to what extent these environmental preferences drive genomic diversity of prokaryotes and to what extent phylogenetic constraints limit this diversification; 3) explore natural nucleotide identity thresholds to delineate species in bacteria in metagenomics gene catalogs; 4) explore species delineation for applications in subspecies and strain delineation in metagenomics. The first part of the thesis describes methods to infer environmental preferences of microbial species. This data is a prerequisite for the analyses performed in the second part of the thesis which explores how the structure of bacterial pangenomes is predetermined by past evolutionary history and how is it linked to environmental preferences of the species. The main finding in this subchapter that habitat preferences explained up to 49\% of the variance for pangenome structure, compared to 18\% by phylogenetic inertia. In general, this trend indicates that phylogenetic inertia does not limit evolution of pangenome size and diversity, but that convergent evolution may overcome phylogenetic constraints. In this project we show that core genome size is associated with higher environmental ubiquity of species. It is likely this is due to the fact that species need to have more versatile genomes and most necessary genes need to be present in majority of genomes of that species to be highly prevalent. Taken together these findings may be useful for future predictive analyses of ecological niches in newly discovered species. The third part of the thesis explores data-driven, operational species boundaries. I show that homologous genes from the same species from different genomes tend to share at least 95\% of nucleotide identity, while different species within the same genus have lower nucleotide identity. This is in line with other studies showing that genome-wide natural species boundary might be in range of 90-95\% of nucleotide identity. Finally, the fourth part of the thesis discusses how challenges in species delineation are relevant for the identification of meaningful within-species groups, followed by a discussion on how advancements in species delineation can be applied for classification of within-species genomic diversity in the age of metagenomics.},
  subject      = {Pangenom},
  language  = {en}
}
@phdthesis{Kessie2021,
  author    = {Kessie, David Komla},
  title     = {Characterisation of Bordetella pertussis virulence mechanisms using engineered human airway tissue models},
  doi       = {10.25972/OPUS-23571},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-235717},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {Pertussis is a highly contagious acute respiratory disease of humans which is mainly caused by the gram-negative obligate human pathogen Bordetella pertussis. Despite the availability and extensive use of vaccines, the disease persists and has shown periodic re-emergence resulting in an estimated 640,000 deaths worldwide in 2014. The pathogen expresses various virulence factors that enable it to modulate the host immune response, allowing it to colonise the ciliated airway mucosa. Many of these factors also directly interfere with host signal transduction systems, causing damage to the ciliated airway mucosa and increase mucous production. Of the many virulence factors of B. pertussis, only the tracheal cytotoxin (TCT) is able to recapitulate the pathophysiology of ciliated cell extrusion and blebbing in animal models and in human nasal biopsies. Furthermore, due to the lack of appropriate human models and donor materials, the role of bacterial virulence factors has been extrapolated from studies using animal models infected with either B. pertussis or with the closely related species B. bronchiseptica which naturally causes respiratory infections in these animals and produces many similar virulence factors. Thus, in the present work, in vitro airway mucosa models developed by co-culturing human airway epithelia cells and fibroblasts from the conduction zone of the respiratory tract on a decellularized porcine small intestine submucosa scaffold (SISser®) were used, since these models have a high correlation to native human conducting zone respiratory epithelia. The major aim was to use the engineered airway mucosa models to elucidate the contribution of B. pertussis TCT in the pathophysiology of the disease as well as the virulence mechanism of B. pertussis in general. TCT and lipopolysaccharide (LPS) either alone or in combination were observed to induce epithelial cell blebbing and necrosis in the in vitro airway mucosa model. Additionally, the toxins induced viscous hyper-mucous secretion and significantly disrupted barrier properties of the in vitro airway mucosa models. This work also sought to assess the invasion and intracellular survival of B. pertussis in the polarised epithelia, which has been critically discussed for many years in the literature. Infection of the models with B. pertussis showed that the bacteria can adhere to the models and invade the epithelial cells as early as 6 hours post inoculation. Invasion and intracellular survival assays indicated the bacteria could invade and persist intracellularly in the epithelial cells for up to 3 days. Due to the novelty of the in vitro airway mucosa models, this work also intended to establish a method for isolating individual cells for scRNA-seq after infection with B. pertussis. Cold dissociation with Bacillus licheniformis subtilisin A was found to be capable of dissociating the cells without inducing a strong fragmentation, a problem which occurs when collagenase and trypsin/EDTA are used. In summary, the present work showed that TCT acts possibly in conjunction with LPS to disrupt the human airway mucosa much like previously shown in the hamster tracheal ring models and thus appears to play an important role during the natural B. pertussis infection. Furthermore, we established a method for infecting and isolating infected cells from the airway mucosa models in order to further investigate the effect of B. pertussis infection on the different cell populations in the airway by single cell analytics in the future.},
  subject      = {Tissue engineering},
  language  = {en}
}
@phdthesis{Breyer2021,
  author    = {Breyer, Charles Pierre Paul},
  title     = {Putative Eisenregulation von Fractalkin (CX3CL1), pathophysiologische Rolle von CX3CL1 in Pl{\"a}ttchenmodellen und Eisenhaushalt in der Megakaryopoese},
  doi       = {10.25972/OPUS-23792},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-237929},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {In dieser Arbeit wird gezeigt, dass Fractalkin (CX3L1) keine Eisenregulation im Sinne des klassischen IRE/IRP-Systems aufweist. Zus{\"a}tzlich wird die pathophysiologische Rolle der CX3CL1/CX3CR1-Achse in Megakaryozyten untersucht. Ferner wird die Eisenhom{\"o}ostase w{\"a}hrend der megakaryopetischen Differenzierung erforscht.},
  subject      = {Fractalkin},
  language  = {de}
}
@phdthesis{Heimberger2024,
  author    = {Heimberger, Kevin},
  title     = {Regulation pathways of c-MYC under glutamine-starving conditions in colon carcinoma cells},
  doi       = {10.25972/OPUS-36331},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-363316},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2024},
  abstract  = {Colon carcinomas (CRC) are statistically among the most fatal cancer types and hence one of the top reasons for premature mortality in the developed world. CRC cells are characterized by high proliferation rates caused by deregulation of gene transcription of proto-oncogenes and general chromosomal instability. On macroscopic level, CRC cells show a strongly altered nutrient and energy metabolism. This work presents research to understand general links between the metabolism and transcription alteration. Mainly focussing on glutamine dependency, shown in colon carcinoma cells and expression pathways of the pro-proliferation protein c-MYC. Previous studies showed that a depletion of glutamine in the cultivation medium of colon carcinoma cell lines caused a proliferation arrest and a strong decrease of overall c-MYC levels. Re-addition of glutamine quickly replenished c-MYC levels through an unknown mechanism. Several proteins altering this regulation mechanism were identified and proposed as possible starting point for further in detail studies to unveil the precise biochemical pathway controlling c-MYC translation repression and reactivation in a rapid manner. On a transcriptional level the formation of RNA:DNA hybrids, so called R-loops, was observed under glutamine depleted conditions. The introduction and overexpression of RNaseH1, a R-loop degrading enzyme, in combination with an ectopically expressed c-MYC variant, independent of cellular regulation mechanisms by deleting the regulatory 3'-UTR of the c-MYC gene, lead to a high rate of apoptotic cells in culture. Expression of a functionally inactive variant of RNaseH1 abolished this effect. This indicates a regulatory function of R-loops formed during glutamine starvation in the presence of c-MYC protein in a cell. Degradation of R-loops and high c-MYC levels in this stress condition had no imminent effect on the cell cycle progression is CRC cells but disturbed the nucleotide metabolism. Nucleotide triphosphates were strongly reduced in comparison to starving cells without R-loop degradation and proliferating cells. This study proposes a model of a terminal cycle of transcription termination, unregulated initiation and elongation of transcription leading to a depletion of energy resources of cells. This could finally lead to high apoptosis of the cells. Sequencing experiments to determine a coinciding of termination sites and R-loop formation sides failed so far but show a starting point for further studies in this essential survival mechanism involving R-loop formation and c-MYC downregulation.},
  subject      = {Myc},
  language  = {en}
}