12033 research outputs found
Sort by
Investigations on structure and biosynthesis of ribosomal peptide natural products involved in a tripartite mutualistic interaction
No full text(noch nicht zugänglich / not yet accessible
On the enigmatic mechanism of signal transduction of "arrestin-biased" angiotensin peptides: spotlight on endogenous angiotensin 1-7
No full text(noch nicht zugänglich / not yet accessible
Multi-layer single-cell omics applications in the context of infection
No full textSingle cell multi-omics sequencing techniques have seen rapid developments in the last few years. The ability of pairing different data modalities makes it an attractive tool for investigating adaptive immune responses. This thesis consists of three projects, which share the common goal of gaining comprehensive insight into T cell biology through single cell multi-omics approaches.
Initially, in this thesis I review major developments in the capture of single cell adaptive immune receptor repertoires (AIRR) in parallel with other single cell omics modalities. In addition, I summarise work conducted over four years to establish a framework for generating and analysing paired single cell RNA- and AIRR-sequencing data using single cell techniques available in our department.
Building on this, we developed a comprehensive workflow to collect multi-omics single-cell data using the BD Rhapsody platform. This included whole transcriptome, cell surface markers (targeted sequencing-based cell surface proteomics), T cell specificities, AIRR profiles and sample multiplexing. With this technique I identified novel paired T-cell receptor sequences for three prominent HCMV epitopes. In addition, I review the ability of dCODE Dextramers to detect antigen-specific T cells at low frequencies by estimating sensitivities and specificities when used as sequencing reagents.
In the final chapter of this thesis, we examine the kinetics of genome-wide changes in gene expression and chromatin accessibility, as well as temporal dynamics of transcription factor (TF) regulation early after Influenza A infection. We do this by tracking transgenic OT-I CD8+ T cells through the first divisions early after infection with recombinant Influenza A/Hong Kong/x31-OVA257-264 virus. We found that type I interferons served as an initial inflammatory trigger in undivided T cells, which instigated chromatin remodelling in genomic regions associated with TCR activation. Our chromatin accessibility data suggests that this happens in an IRF1 dependent manner. Remarkably, IFN-I signalling in undivided T cells was temporally limited. Upon antigen encounter, major chromatin restructuring occurred in undivided T cells, with SMARCC1 as a putative transcriptional regulator. For cells transitioning into the division phase, the positive TF regulators BATF and BATF3 were identified, aligning with their established roles in early effector differentiation. In a broader context, these findings offer a comprehensive view of how transcription factors govern gene expression during the initial cell divisions following infection, serving as a valuable resource for future investigations into early fate decisions of CD8+ T cells.
In summary, the emerging field of multi-layer single-cell omics is set to reshape our understanding of adaptive immune responses by providing unprecedented insight into cellular heterogeneity, differentiation, and function. The work presented here demonstrates practical applications of these technologies and highlights their potential to transform the study of adaptive immunity in the future
Morphologic adaptations and hydrodynamics of 'pelvic brooding', a derived reproductive strategy in Sulawesi ricefishes (Beloniformes: Adrianichthyidae)
No full text(noch nicht zugänglich / not yet accessible
Medicinal Chemistry and Pharmacology of Ectonucleotidases: Assay Development and Characterisation of Inhibitors
No full text(noch nicht zugänglich / not yet accessible
Reprogramming Borohydride Reactivity by Integrating Titanium and Chromium in Cooperative Catalysis
No full text(noch nicht zugänglich / not yet accessible
Effects of <em>Bacillus firmus</em> and Bacterial Secondary Metabolites on the Plant Parasitic Nematode <em>Heterodera schachtii</em> : Impact Assessment and Mechanistic Insights
No full textPlant-parasitic nematodes cause enormous yield losses and economic damage to a wide range of economically important crops. Although synthetic chemicals can be effective in controlling plant-parasitic nematodes, their use raises significant environmental and health concerns. In this context, bio-based control strategies, particularly those utilizing microbes and microbial compounds, have emerged as promising alternatives.
Our studies aim to explore the efficacy and mechanism of action of Bacillus firmus I-1582 and the bacterial secondary metabolites prodiginines and rhamnolipids as microbial control agents against the beet cyst nematode Heterodera schachtii using a multidisciplinary approach involving microbiology, molecular biology and bioinformatics.
Chapters 2 and 3 present a comprehensive investigation of the potential of B. firmus I-1582 for biological control of H. schachtii. We have shown that B. firmus I-1582 can be attracted to Arabidopsis thaliana root exudates and that its colonization and development at the root of the host is pH-dependent. We also show that living bacterial cells clearly protect A. thaliana from infestation by H. schachtii. In contrast, dead bacterial cells or culture supernatant show no such effect. Interestingly, the living cells of B. firmus I-1582 also inhibit the infection, development and reproduction of the next generation juveniles. Since bacterial colonization of the host roots is not pronounced, no bacterial biofilm is present to prevent invasion of the invading J2 infective juveniles. We hypothesize that the 2nd generation J2 are less fit and that active molecules secreted by B. firmus I-1582 may have an inhibitory effect on the nematodes. In another experiment, direct contact of the cell-free supernatant with H. schachtii juveniles was shown to have a significant nematicidal effect when formed at higher temperatures. This lethal effect can be attributed to small molecules produced by B. firmus I-1582 under these conditions. Their molecular weight is below ~3 kDa and they are both protease-sensitive and protease-resistant. Using genome mining tools, a biosynthetic gene cluster was identified in the genome of B. firmus I-1582 encoding three putative lanthipeptides that are potential compounds active against nematodes. Gene expression analysis confirms the upregulation of all three putative lanthipeptide genes in B. firmus I-1582 and thus their presence in the culture supernatant.
In Chapter 4, the use of prodiginines alone and together with rhamnolipids as active substances against nematodes is investigated. We observed that prodiginines remarkably inhibited parasitism of H. schachtii on its host plant by reducing the motility of J2 and the activity of the mouth stylet as an indicator of J2 infection activity. In addition, we investigated the synergistic effect of prodiginines and rhamnolipids for the first time and found that the application of both substances is more effective against the nematodes than the application of either substance alone.
We are convinced that this research can improve the fundamental understanding and practical implementation of microbial-based control strategies and drive the development of innovative and sustainable solutions for integrated nematode management
Forecasting Tools and Risk Prediction Models for Decision Support in Fruit Production
No full textTree fruit production in Germany is confronted with various risks that affect quality and reduce yields, such as disease infestation or weather events. The occurrence of late spring frosts often leads to cell damage, resulting in yield reduction and reduced fruit quality, e.g. due to 'frost rings' on the peel. With ongoing climate change, fruit trees tend to bloom earlier, which goes along with an increase in spring frost frequency during the last years in some regions.
In this thesis, I applied the decision analysis methodology to develop probabilistic models. Decision analysis allows for the inclusion of expert knowledge into the modelling procedure and accounts for uncertainty and variability of the model parameter values. Furthermore, I used Kriging Interpolation and process-based phenology modelling to produce countrywide maps of historic and future frost risk in apple production.
1. In chapter 2, I introduce ProbApple a model to make probabilistic forecasts of total apple yield and high-quality yield at four time points during the growing season (at full bloom, before fruit thinning, after June drop, and four weeks before harvest). Using a case study on 'Gala' apple in Rhineland, we showed the functionality and structure of the model and compared the high-quality yield in orchards with and without anti-hail netting.
2. In chapter 3, I analyze the frost frequency during and after apple bloom in the time periods 1993-2007 and 2007-2022 based on historic temperature and phenology data. We observed a trend toward earlier apple bloom and increasing frost frequency across nearly in the whole country. Frosts below 0°C occurred in all apple production regions, while only during a few frost events the temperatures fell below -2.2°C.
3. In chapter 4, I describe a decision support model to advise apricot producers on investments in frost protection. We compared yield effects and Net Present Value of candles, below-canopy irrigation, as well as mobile and stationary wind machines in relation to apricots production without frost protection. Despite an appreciable increase in yield, the additional income was not sufficient to cover the additional costs for frost protection.
4. In chapter 5, I present a comparison of eight frost protection measures (mobile or stationary wind machines, portable or tractor-mounted gas heaters, overhead or below-canopy irrigation, candles and pellet heaters) regarding their economic efficiency and yield effects in apple production using decision analysis. It turned out that overhead irrigation and stationary wind machines appear to be the most promising frost protection measures, but they do not necessarily increase farmers' revenues.
5. In chapter 6, I show maps for the future spring frost risk in German apple production from green tip stage until summer under four climate change scenarios for the years 2050 and 2085. The phenology forecast indicates that the current trend towards earlier apple blossom will continue in future. The effect of climate change of frost risks differs between regions and climate change scenarios. However, we showed that late spring frost will remain a challenge for apple production even at the end of the 21st century.
Overall, the forecasting tools, risk prediction models, and their results in this thesis may be useful for fruit growers to make informed decisions in short- and long-term planning. They can be used by policymakers as a reliable source of information and serve scientists as a base for further development of probabilistic models in fruit production.Die Baumobsterzeugung in Deutschland, ist mit vielseitigen Risiken konfrontiert, welche die Qualität beeinträchtigen und die Erträge mindern, z. B. Krankheitsbefall oder Wetterereignisse. Das Auftreten von Spätfrösten im Frühjahr führt häufig zu Zellschäden und damit zu Ertragsminderungen und reduzierter Fruchtqualität, z. B. durch "Frostringe" auf der Schale. Mit dem fortschreitenden Klimawandel blühen Obstbäume tendenziell früher, was in einigen Regionen mit einer Zunahme der Spätfrosthäufigkeit in den letzten Jahren einherging.
In dieser Arbeit habe ich die Methodik der Entscheidungsanalyse angewandt, um probabilistische Modelle zu entwickeln. Die Entscheidungsanalyse ermöglicht es, Expertenwissen in das Modell einzubeziehen und die Unsicherheit und Variabilität der Modellparameterwerte zu berücksichtigen. Darüber hinaus habe ich Kriging-Interpolation und prozessbasierte phänologische Modellierung verwendet, um landesweite Karten des Frostrisikos im Apfelanbau zu erstellen.
1. In Kapitel 2 stelle ich ProbApple vor, ein Modell zur probabilistischen Vorhersage des Gesamtertrags und des Qualitätsertrags von Äpfeln zu vier Zeitpunkten während der Vegetationsperiode (zur Vollblüte, vor dem Ausdünnen der Früchte, nach dem Junifall und vier Wochen vor der Ernte). Anhand einer Fallstudie über den Apfel 'Gala' im Rheinland zeigen wir die Funktionsweise und Struktur des Modells und vergleichen den Qualitätsertrag in Obstanlagen mit und ohne Hagelschutznetz.
2. In Kapitel 3 analysiere ich die Frosthäufigkeit während und nach der Apfelblüte in den Zeiträumen 1993-2007 und 2008-2022 anhand von historischen Temperatur- und Phänologiedaten. Wir konnten wir einen Trend zu einer früheren Apfelblüte und einer zunehmenden Frosthäufigkeit in fast ganz Deutschland feststellen. Fröste unter 0°C traten in allen Apfelanbauregionen auf, während die Temperaturen nur bei wenigen Frostereignissen unter 2,2 °C fielen.
3. In Kapitel 4 beschreibe ich ein Entscheidungsmodell zur Beratung von Aprikosenproduzenten hinsichtlich einer Investitionen in Frostschutz. Wir haben den Ertragseffekt und den Kapitalwert von Kerzen, Unterkronenbewässerung sowie mobilen und stationären Windmaschinen im Verhältnis zur Aprikosenproduktion ohne Frostschutz verglichen. Trotz einer deutlichen Ertragssteigerung reichten die zusätzlichen Erträge nicht aus, um die Mehrkosten für den Frostschutz zu decken.
4. In Kapitel 5 stelle ich einen Vergleich von acht Frostschutzmaßnahmen (mobile oder stationäre Windmaschinen, mobile oder traktormontierte Gasheizgeräten, Überkronen- oder Unterkronen-bewässerung, Kerzen und Pelletheizungen) hinsichtlich ihrer Wirtschaftlichkeit und Ertragseffekte im Apfelanbau mittels Entscheidungsanalyse vor. Es zeigte sich, dass Überkronenberegnung und stationäre Windmaschinen die vielversprechendsten Frostschutzmaßnahmen zu sein scheinen, aber nicht unbedingt die Einnahmen der Landwirte erhöhen.
5. In Kapitel 6 zeige ich Karten für das zukünftige Spätfrostrisiko in der deutschen Apfelproduktion vom Blattknospenaufbruch bis zum Sommer unter vier Klimawandelszenarien für die Jahre 2050 und 2085. Die Phänologieprognose zeigt, dass sich der derzeitige Trend zur früheren Apfelblüte auch in Zukunft fortsetzen wird. Die Auswirkungen des Klimawandels auf die Frostgefahr sind je nach Region und Klimawandelszenario unterschiedlich. Wir haben jedoch gezeigt, dass Spätfröste auch am Ende des 21. Jahrhunderts noch eine Herausforderung für die Apfelproduktion darstellen werden.
Insgesamt können die Prognoseinstrumente, Risikovorhersagemodelle und ihre Ergebnisse in dieser Arbeit für Obstbauern nützlich sein, um fundierte Entscheidungen für die kurz- und langfristige Planung zu treffen. Sie können von politischen Entscheidungsträgern als zuverlässige Informationsquelle genutzt werden und Wissenschaftlern als Grundlage für die weitere Entwicklung probabilistischer Modelle im Obstbau dienen
Low-Valent Heavier Tetrel Compounds Supported by N-heterocyclic Carbenes: A Comprehensive Experimental and Theoretical Perusal
No full text(noch nicht zugänglich / not yet accessible
The economics of carbon sequestration in African agriculture
No full textThe growing recognition of food systems and agricultural soils for climate change adaptation and mitigation has not yet been matched by investment and action at scale. Carbon markets have the potential to mobilize financing and incentivize sustainable agricultural practices, but their scale within the agricultural sector remains marginal. In three essays, this dissertation explores how agricultural carbon markets in Africa can be operationalized and scaled.
The first essay explores the soil organic carbon (SOC) dynamics of smallholder farmers in Western Kenya. It draws on a unique dataset that combines household- and plot-level primary data from 494 smallholder farmers with secondary spatial data. The study quantifies the soil carbon sequestration potential of smallholder farmers and its determinants. The results show average increases in SOC concentrations between 6.7 and 11.3 g/kg, which translate into average annual increases in SOC stocks ranging from 3.1 to 7.1 t C/ha. Seasonal fluctuations emerged as a potentially significant driver of SOC variability, complicating attributions of SOC changes to specific farming practices. Satellite-based carbon farming indices reveal a significant and measurable association with SOC, though low in magnitude.
The second essay evaluates a portable near-infrared (NIR) scanner as a cost-effective alternative to traditional laboratory analyses, using primary data from 102 plots in Siaya County, Kenya. The study evaluates the scanner's predictive performance under field conditions in comparison to laboratory benchmarks, examines the consistency of SOC measurements through repeat analyses, and assesses the extent to which measurement errors influence SOC stock calculations. The results indicate a weak correlation between scanner predictions and laboratory measurements (R² = 0.10-0.11, RMSE = 5.62-7.12 g/kg), with the scanner generally underestimating SOC. However, the results also showed low reproducibility and repeatability of SOC measurements within and across different laboratories. Simulations of the impact of measurement error on SOC stock calculations reveal high variability across all measurement approaches that limit possibilities for result-based payments for carbon sequestration.
The third essay explores how agricultural carbon markets can attract private investments into Africa's agricultural sector. The study draws on case study evidence from twelve carbon farming projects in Kenya, combining insights from interviews conducted in 2023 and a detailed analysis of project documentation. The study explores alternative carbon farming business models implemented in Kenya and assesses their economic viability and inclusiveness. The study identifies four business models that differ in the source of funding and financing conditions. A comparative assessment of their economic viability and inclusiveness highlights critical lessons, including the importance of financing terms, achieving scale, transparent benefit-sharing, bottom-up approaches, and reducing reliance on international intermediaries.
Together, the three essays provide complementary insights into the biophysical, technological, and institutional dimensions of carbon farming in Africa, offering practical guidance for project developers, financers, and policymakers in Africa and beyond to support the development and scaling of agricultural carbon markets