Refine
Year of publication
- 2021 (141) (remove)
Document Type
- Doctoral Thesis (141) (remove)
Language
- English (141) (remove)
Has Fulltext
- yes (141)
Is part of the Bibliography
- no (141)
Keywords
- 2D materials (1)
- AIFMD (1)
- ALICE upgrade (1)
- Acetogenic bacteria (1)
- Akute lymphoblastische Leukämie (1)
- Alignment (1)
- Alterung (1)
- Approximation Algorithms (1)
- Architecture (1)
- Astrophysics (1)
- Autographisches Gedächtnis (1)
- Bayesian Persuasion (1)
- Biodiversity (1)
- Biomarker (1)
- Biopysikalische Chemie (1)
- Biotic interactions (1)
- Blue Hole (1)
- Bohmian mechanics (1)
- Bulgaria (1)
- CBM Experiment (1)
- CD45RA Depletion (1)
- CHIP (1)
- CXCL13 (1)
- CXCR5 (1)
- Cancer (1)
- Carbon capture (1)
- Caribbean (1)
- Checkpoint Inhibitor (1)
- China (1)
- Climate change (1)
- Cognitive Interviews (1)
- Color superconductivity (1)
- Colorectal Cancer (1)
- Computer Vision (1)
- Control System (1)
- Croatia (1)
- Cross-cultural Comparability (1)
- DNA (1)
- DNP (1)
- Delegated Search (1)
- Developmental Biology (1)
- EPICS (1)
- Erzählung (1)
- Faltungsdynamik (1)
- Fatty acid synthases (1)
- Financialisation (1)
- Financialization (1)
- Flavoproteins (1)
- Freshwater Ecosystems (1)
- Functional traits (1)
- G-Quadruplex (1)
- Geochemie, Bivalve, Koralle, Foraminifere (1)
- Gravitational Waves (1)
- Gravity's Rainbow (1)
- Herrschaft (1)
- Hochenergiephysik (1)
- Hydrogen storage (1)
- Hydrogen-dependent CO2 reductase (1)
- Infinite Jest (1)
- Internationale Beziehungen (1)
- Intertextuality (1)
- Isopoda (1)
- KR2 (1)
- Kinetik (1)
- Knochenmarksmikromilieu (1)
- MEK inhibition (1)
- Makrophagen (1)
- Malaysian English literature (1)
- Malaysian literature (1)
- Measurement Invariance (1)
- Metabolism (1)
- Metasurfaces (1)
- Methyltransferase (1)
- Micro Vertex Detector (1)
- Microbiology (1)
- Monocular Scene Flow (1)
- Multimessenger (1)
- NMR (1)
- Neurotoxicity (1)
- Neutron Star (1)
- Non-canonical terpenes (1)
- Numerical Relativity (1)
- Observation Deck (1)
- Online Algorithms (1)
- Organic micropollutants (1)
- Organoids (1)
- Paramecium (1)
- Parkinson (1)
- Phase diagram (1)
- Philippines (1)
- Photochemie (1)
- Pink1 (1)
- Polyketide synthases (1)
- Practice Theory (1)
- Praxistheorie (1)
- Prenyl pyrophosphates (1)
- Private Equity (1)
- Protein engineering (1)
- Quantum chromodynamics (1)
- Question Under Discussion (1)
- RMN (1)
- RNA biology (1)
- RNA interference (1)
- Repair (1)
- Riccati equation (1)
- Risk assessment (1)
- Rule (1)
- Russia (1)
- Scattering-type Scanning Near-field Optical Microscopy (1)
- Schistosomiaisis (1)
- Serbia (1)
- Sodium ion pump (1)
- South-Eastern Europe (1)
- Special Autonomic Policy, Social Political Movements, Papua (1)
- Spectacle (1)
- Speculation (1)
- THz (1)
- Teaching Quality (1)
- TeraFET (1)
- Terpenes (1)
- Tradition (1)
- Traffic Scenes (1)
- Ulysses (1)
- Western Kenya (1)
- X-ray crystallography (1)
- Zolpidem; Food-effect, PBBM, PBPK (1)
- academic writing (1)
- age (1)
- application (1)
- atherosclerosis (1)
- authoritarian systems (1)
- autocracy (1)
- autologous stem cell transplantation (1)
- brain waves (1)
- cMYC (1)
- chemotherapy (1)
- climate (1)
- clonal dominance (1)
- clonal hematopoiesis (1)
- closed orbit feedback system (1)
- cluster computing (1)
- counter-terrorism (1)
- cryo-EM (1)
- debugging (1)
- detector (1)
- developmental states (1)
- discourse structure (1)
- distinctive linguistic features (1)
- endothelial cell (1)
- epigenome (1)
- erstarrte Trauer (1)
- field-effect transistor (1)
- fundamental theorem of asset pricing (1)
- gender (1)
- geology (1)
- hTERT (1)
- heart failure (1)
- heavy-ion physics (1)
- hematopietic stress (1)
- hematopoietic stem cells (1)
- high performance computing (1)
- high-energy physics (1)
- hurricane (1)
- industrial policy (1)
- inflammation (1)
- infra-slow oscillation (1)
- legitimacy (1)
- leukemia (1)
- low-mass dilepton (1)
- macronucleus (1)
- mechanics (1)
- mitochondrial dysfunction (1)
- mounting (1)
- no unbounded profit with bounded risk (1)
- npas4l (1)
- paleoanthropology (1)
- paleoecology (1)
- paleontology (1)
- palynology (1)
- pharmacokinetics (1)
- popular fiction (1)
- pronephric duct (1)
- propagating waves (1)
- proportional transaction costs (1)
- quantum hydrodynamics (1)
- quantum mechanics (1)
- quark-gluon plasma temperature (1)
- reptiles (1)
- rhodopsin (1)
- sea-surface-temperature (1)
- section-feature mapping (1)
- self-definierende Erinnerung (1)
- semimartingales (1)
- sexuality (1)
- shroom (1)
- sleep (1)
- small RNA (1)
- solid-state NMR (1)
- somatic mutations (1)
- stochastic integration (1)
- terrorism (1)
- uneindeutiger Verlust (1)
- vasculogenesis (1)
- zebrafish (1)
Institute
- Biowissenschaften (40)
- Biochemie, Chemie und Pharmazie (28)
- Physik (26)
- Informatik und Mathematik (12)
- Medizin (7)
- Geowissenschaften / Geographie (5)
- Gesellschaftswissenschaften (4)
- Neuere Philologien (4)
- Biochemie und Chemie (3)
- Geowissenschaften (2)
Clean water is fundamental to human health and ecosystem integrity. However, water quality deteriorates due to novel anthropogenic pollutants present at microgram per liter concentrations in urban water cycles (termed micropollutants). Wastewater treatment plants (WWTP) have been identified as major point sources for aquatic (micro-)pollutants. Chemical and ecotoxicological analyses have shown that conventional biological WWTPs do not fully remove micropollutants and associated toxicities, which is often because of mobile, polar and/or recalcitrant compounds and transformation products (TPs). To minimize possible environmental risks, advanced wastewater treatment (AWWT) technologies could be a promising mitigation measure. Multiple processes are therefore being developed and evaluated such as ozonation and ozonation followed by granulated activated carbon (GAC) or biological filtration. Assessing the performance of these combined AWWTs was the focus the TransRisk project. Within this project, this thesis accomplished four major goals.
Firstly, the preparation of (waste)water samples was optimised for in vitro bioassays. Acidification, filtration and solid phase extraction (SPE) were tested for their impact on environmentally relevant in vitro endocrine activities, mutagenicity, genotoxicity and cytotoxicity. Significantly different outcomes of these assays were detected comparing neutral and acidified samples. Sample filtration had a lesser impact, but in some cases retention of particle-bound compounds could have caused significant toxicity losses. Out of three SPE sorbents the Telos C18/ENV at sample pH 2.5 extracted highest toxicity, some undetected in aqueous samples. These results indicate that sample preparation needs to be optimised for specific sample matrices and bioassays to avoid false-positive or -negative detects in effect-based analyses.
Secondly, the above listed in vitro toxicities were monitored in a protected region for drinking water production in South-West Germany (2012-2015). Out of 30 sampling sites surface water and groundwater were the least polluted. Nonetheless, a few groundwater samples induced high anti-estrogenic activity that prompted further monitoring. The latter included a waterworks in which no toxicity was detected. Hospital wastewater also had elevated in vitro toxicities and hospitals are, thus, relevant intervention points for source control. The biological WWTPs were effective in removing most of the detected toxicity, and the selected bioassays proved to be pertinent tools for water quality assessment and prioritisation of pollution hotspots.
Thirdly, the in vivo bioassay ISO10872 based on Caenorhabditis elegans (C. elegans) was adapted for this thesis. Using this model, a median effect concentration (EC50) for reproductive toxicity of the polycyclic aromatic hydrocarbon β-naphthoflavone (β- NF) of 114 µg/L was computed which is slightly lower than reported in the scientific literature. β-NF induced cyp-35A3::GFP (a biomarker in transgenic animals) in a time and concentration dependent manner (≤ 21.3–24 fold above controls). β-NF spiked wastewater samples supported earlier hypotheses on particle-bound pollutants. Reproductive toxicity (96 h) and cyp-35A3 induction (24 h) of biologically treated and/or ozonated wastewater extracts and growth promoting effects of GAC/biologically filtered ozonated wastewater extracts were observed. This suggested the presence of residual bioactive/toxic chemicals not included in the targeted chemical analysis. It also highlighted the importance of integrating multiple (apical and molecular) endpoints in wastewater assessments.
Fourthly, five in vitro and the adapted C. elegans bioassay were integrated into a wastewater quality evaluation (developed within TransRisk). Out of the five AWWT options, ozonation (at 1 g O3,applied/g DOC, HRT ~ 18 min) combined with nonaerated GAC filtration was rated most effective for toxicity removal. All five AWWTs largely removed estrogenic and (anti-)androgenic activities, but not anti-estrogenic activity and mutagenicity, which even increased during ozonation. This has been observed in related studies and points towards toxic TPs. These results also emphasized the need for implementing an effective post-treatment for ozonation. The results from a parallel in vivo study with Lumbriculus variegatus and Potamopyrgus antipodarum conducted on site at the WWTP (using flow through systems) were in accordance with the C. elegans results. In this context, it is suggested to further implement C. elegans as sensitive, feasible and ecologically relevant model.
In conclusion, this thesis shows how optimised sample preparation, long-term (in vitro) environmental monitoring, sensitive and ecologically relevant (in vivo) bioassays as well as innovative evaluation concepts, are pivotal in improving the removal of micropollutants and their toxicities with AWWTs. Future research should further develop and evaluate measures at sewer systems, conventional biological, tertiary and other advanced treatment technologies, as well as sociopolitical strategies (e.g., source control or natural conservation) and restoration projects. The effect-based tools optimised in this thesis will support assessing their success.
In the past decades, the use and production of chemicals has been on the rise globally due to increasing industrialization and intensive agriculture; resulting in the occurrence and ecotoxicological risks of chemicals of emerging concern (CECs) in the aquatic compartments. Risks include changes in community structure resulting in the dominance of one species and ecosystem imbalance. When dominant disease-causing organisms are in the environment, the disease transmission is increased. For example, host snails for the schistosomiasis, a human trematode disease, are known to be tolerant to pesticide
exposure compared to the predators. This would therefore result in an increased abundance of snails which consequently increase the disease transmission in the human population.
Kenya, being a low income country faces a lot of challenges with provision of clean water, diseases and sanitation facilities, and increasing population which results in intensive agriculture coupled with pesticide use. Although a lot of research has been carried out on the environmental occurrence and risk of CECs (Chapter 1), most of these studies have been done in developed countries with limited information from Africa. Additionally, research in Africa focused on urban areas with limited number of compounds analyzed and mostly in the water phase, and inadequate information on the effects of CECs on the aquatic organisms. In order to reduce this knowledge gap, this dissertation focused on identification and quantification of CECs present in water, sediment and snails from western Kenya, and the contribution of pesticides to the transmission of schistosomiasis.
Chapter 2 gives a summary of the results and discussion of the dissertation. In Chapter 3, a comprehensive chemical analysis was carried out on 48 water samples to identify compounds, spatial patterns and associated risks for fish, crustacean and algae using toxic unit (TU) approach. A total of 78 compounds were detected with pesticides and biocides being the compounds most frequently detected. Spatial pattern analysis revealed limited compound grouping based on land use. Acute risk for crustaceans and algae were driven by one to three individual compounds. These compounds responsible for toxicity were prioritized as candidate compounds for monitoring and regulation in Kenya.
In Chapter 4, an extension of Chapter 3 was done to cover the CECs present in snails and sediment from the 48 sites. A total of 30 compounds were found in snails and 78 in sediments with 68 additional compounds being found which were not previously detected in water. Higher contaminant concentrations were found in agricultural sites than in areas without anthropogenic activities. The highest acute toxicity (TU 0.99) was determined for crustaceans based on compounds in sediment samples. The risk was driven by diazinon and pirimiphos-methyl. Acute and chronic risks to algae were driven by diuron whereas fish were found to be at low to no acute risk.
In Chapter 5, the effect of pesticide contamination on schistosomiasis transmission was evaluated by applying complimentary laboratory and field studies. In the field studies, the ecological mechanisms through which pesticides and physical chemical parameters affect host snails, predators and competitors were investigated. Pesticide data was obtained from the results in chapter 3. The overall distribution of grazers and predators was not affected by pesticide pollution. However, within the grazers, pesticide pollution increased dominance of host snails. On the contrary, the host-snail competitors were highly sensitive to pesticide exposure. For the laboratory studies, macroinvertebrates including Schistosoma-host snails, competitors and predators were exposed to 6 concentrations levels of imidacloprid and diazinon. Snails showed higher insecticide tolerance compared to competitors and predators. Finally, Chapter 6 summarizes the conclusions of this dissertation, placing it in a broader
context. In this dissertation, a comprehensive chemical characterization and risk assessment of CECs has been carried out in freshwater systems; together with the effects of pesticides on schistosomiasis transmission in rural western Kenya. Results of this dissertation showed that rural areas are contaminated posing a risk to aquatic organisms which contribute to schistosomiasis transmission. This shows the need for regular monitoring and policy formulation to reduce pollutant emissions which contributes negatively to both ecological and human health effects.
The main focus of research in the field of high-energy heavy-ion physics is the study of the quark-gluon plasma (QGP). Topic of the present work is the measurement of electron-positron pairs (dielectrons), which grant direct access to some of the key properties of this state of matter, since after their formation they leave the hot and dense medium without significant interaction. In particular, the measurement of the initial QGP temperature is considered a "holy grail" of heavy-ion physics. Therefore, in addition to the analysis of existing data, a feasibility study has been conducted to determine to which extent this goal would be achievable by upgrading the ALICE experiment at CERN.
Dielectrons are produced during all stages of a heavy-ion collision, with their invariant mass reflecting the amount of energy available at the time of their formation. Dielectrons of highest mass are thus produced in the initial scatterings of the colliding nuclei by quark-antiquark annihilation. Correlated electron-positron pairs can also emerge from the decay chains of early-produced pairs of heavy-flavour (HF) particles. During the QGP stage and at the beginning of the hadronic phase, the system emits thermal radiation in the form of photons and dielectrons, which carry information about the medium temperature to the observer. In the final stage of the collision, decays of light-flavour (LF) hadrons produce additional contributions to the dielectron spectrum.
The present work is based on early data from the ALICE experiment recorded from lead-lead collisions at a center-of-mass energy of 2.76 TeV. Due to the limited amount of data, a focus is placed on achieving high efficiencies throughout the analysis. To this end, a special electron identification strategy is developed and a custom track selection applied, together resulting in a tenfold increase in pair efficiency. The dielectron spectrum is evaluated on a statistical basis, using a pair prefilter, which is optimized based on two signal quality criteria, to reduce the fraction of electrons and positrons from unwanted sources at minimum signal loss. In addition, an artifact of the track reconstruction is exploited to suppress pairs from photon conversions and to correct the dielectron yield for a contribution from different-conversion pairs. The main signal uncertainty is extracted from the deviation between results of 20 analysis settings and amounts to 20% in most of the studied kinematic range.
For comparison with the analysis results, a hadronic cocktail consisting of the LF and HF contributions is simulated, which can reasonably well describe the measured dielectron production, with a hint of an enhancement at low invariant mass. Two approaches to model the in-medium modification of the heavy-flavour are followed, resulting in up to 50% suppression, which creates some additional space for a thermal contribution at intermediate mass.
For a complete comparison between experimental data and theoretical expectation, two model calculations are consulted. The Thermal Fireball Model provides predictions for thermal dielectron radiation from the QGP and hadron gas. The data tends to be better described with these additional thermal contributions. For a comparison with a prediction by the UrQMD model, the HF component of the cocktail is subtracted from the data. This results in better agreement if the HF suppression by in-medium effects is taken into account.
The feasibility study in this work has served as a physical motivation for the ALICE upgrade for LHC Run 3. The precision with which the early temperature of the QGP can be determined via dielectrons is chosen as key observable. A multitude of individual contributions are merged into a fully modeled dielectron analysis. The resulting signal-to-background ratio represents some of the expected systematic uncertainties, while from the significance combined with the planned number of lead-lead collisions a realistic "measurement" with statistical fluctuations around the expected dielectron signal is generated using a Poisson sampling technique. Since the HF yield exceeds the QGP thermal radiation by about an order of magnitude, an additional analysis step exploiting the enhanced track reconstruction is introduced to reduce its contribution by up to a factor of five. The resulting reduction in pair efficiency is overcompensated by an up to hundred times higher collision rate. The entire cocktail is then subtracted from the sampled data to isolate the thermal excess yield. The final analysis of this spectrum shows that the inverse slope of the model prediction, which depends directly on the QGP temperature, can be reproduced within statistical and systematic uncertainties of about 10%.
The promising results of this study have contributed on the one hand to the realization of the ALICE upgrade and to a design decision for the new Inner Tracking System, and at the same time represent exciting predictions for upcoming measurements.
Das Feld der Hochenergie-Schwerionenforschung hat sich der Untersuchung des Quark-Gluon-Plasmas (QGP) gewidmet. Ein QGP ist ein sehr heißer und dichter Materiezustand, der kurz nach dem Urknall für einige Mikrosekunden das Universum füllte. Unter diesen extremen Bedingungen sind die fundamentalen Bausteine der Materie, die Quarks und Gluonen, quasi frei, also nicht in Hadronen eingeschlossen, wie es unter normalen Bedingungen der Fall ist. Hadronen sind Teilchen, die aus Quarks und Gluonen bestehen. Die bekanntesten Hadronen sind Protonen und Neutronen, die Bestandteile von Atomkernen, aus denen, zusammen mit Elektronen, die gesamte bekannte Materie aufgebaut ist.
Um ein QGP im Labor zu erzeugen, lässt man ultrarelativistische schwere Ionen, wie zum Beispiel Pb-208-Kerne, aufeinander prallen. Dies geschieht am CERN, dem größten Kernforschungszentrum der Welt. Der Teilchenbeschleuniger, welcher Protonen und Pb-Kerne beschleunigt und zur Kollision bringt, heißt Large Hadron Collider (LHC) und ist mit 27 km Umfang der größte der Welt. Bei einer einzigen Pb-Pb Kollision am LHC werden mehrere Tausend Teilchen und Antiteilchen erzeugt. Das dedizierte Experiment zur Untersuchung von Schwerionenkollisionen am LHC ist ALICE. ALICE ist mit mehreren Teilchendetektoren ausgerüstet, die es ermöglichen, tausende Teilchen gleichzeitig zu messen und zu identifizieren.
Unter den produzierten Teilchen befinden sich auch leichte Atomkerne, wenngleich diese nur sehr selten erzeugt werden. Die Anzahl der produzierten Teilchen pro Teilchensorte hängt nämlich von deren Masse ab. In Pb-Pb Kollisionen am LHC sinkt die Anzahl der produzierten (Anti)kerne exponentiell um einen Faktor 1/330 bei Hinzufügen jedes weiteren Nukleons. Die Menge an produzierten Teilchen pro Spezies stellt Informationen über den Produktionsmechanismus beim Übergang vom QGP zum Hadrongas zur Verfügung. Hierbei sind leichte (Anti)kerne von besonderem Interesse, da sie vergleichsweise groß sind und ihre Bindungsenergie bis zu zwei Größenordnungen kleiner ist als die Temperaturen, die bei der Erzeugung der Hadronen vorherrschen. Es ist bis heute noch nicht verstanden, wie leichte (Anti)kerne bei diesen Bedingungen erzeugt werden und überleben können.
Für diese Arbeit wurden ca. 270 Millionen Pb-Pb Kollisionen bei einer Schwerpunktsenergie von 5,02 TeV, die von ALICE im November 2018 aufgezeichnet wurden, analysiert. Es wurde die Produktion von (Anti)triton und (Anti)alpha untersucht. Wegen ihrer großen Masse werden beide Kerne sehr selten produziert, bei weitem nicht bei jeder Kollision. Antialpha ist der schwerste Antikern, der jemals gemessen wurde. Aufgrund dieser Seltenheit ist die Größe des zur Verfügung stehenden Datensatzes entscheidend. Es war möglich, das erste jemals gemessene Antialpha-Transversalimpulsspektrum zu extrahieren. Auch für (Anti)triton und Alpha wurden Transversalimpulsspektren bestimmt.
Die Ergebnisse wurden mit theoretischen Modellen und anderen ALICE Messungen verglichen.
Am Ende wird in einem Ausblick auf das kürzlich durchgeführte Upgrade der ALICE Spurendriftkammer (TPC) eingegangen. In der nächsten, bald startenden Datennahmeperiode wird der LHC seine Kollisionsrate erheblich erhöhen, was es ermöglichen wird, mehr als 100 mal so viele Daten wie bisher aufzuzeichnen. Hiervon werden die in dieser Arbeit beschriebenen (Anti)triton- und (Anti)alpha-Analysen beachtlich profitieren. Um mit den erheblich höheren Kollisionsraten zurecht zu kommen, mussten einige Detektoren, unter anderem die TPC, maßgeblich erneuert werden. In den ersten beiden Datennahmeperioden wurde die TPC mit Vieldrahtproportionalkammern betrieben. Diese sind allerdings viel zu langsam für die geplanten Kollisionsraten. Deshalb wurden sie im Jahr 2019, während einer langen Betriebspause des LHC, durch Quadrupel-GEM (Gas Electron Multiplier) Folien basierte Auslesekammern ersetzt, welche eine kontinuierliche Auslese der TPC ermöglichen. Da es sich um die erste jemals gebaute GEM TPC im Großformat handelt, war ein umfangreiches Forschungs- und Entwicklungs- (F&E) Programm notwendig, um die GEM Auslesekammern zu charakterisieren und zu testen. Im Rahmen dieses F&E Programms wurden am Anfang dieser Promotion systematische Messungen an einer kleinen Test TPC mit Quadrupel-GEM Auslese, die extra zu diesem Zweck gebaut worden war, durchgeführt. Hierbei wurde der Rückfluss der bei der Gasverstärkung erzeugten Ionen in das Driftvolumen der TPC und die Energieauflösung mit verschiedenen GEM Folien Typen und unterschiedlicher Anordnung gemessen. Das Ziel war, möglichst kleine Ionenrückflüsse bei möglichst guter Energieauflösung zu erreichen. Hierbei musste ein Kompromiss gefunden werden, da die beiden Größen sich gegenläufig verhalten. Es war jedoch möglich, mit mehreren GEM Konfigurationen Spannungseinstellungen zu identifizieren, bei denen beide Größen den gewünschten Anforderungen entsprachen.
In recent years, several neuronal differentiation protocols were published that circumvent the requirement of embryoid body (EB) formation under serum-deprivation and simplified medium conditions. But a neuronal default model to establish an approach that works efficiently for all pluripotent cells and neuronal precursors is still lacking. Whether such a default neural mechanism exist and how this is implemented across a broad spectrum of cell source, is addressed in several studies and still controversially discussed. It was proposed that the default neuronal fate is initiated in the absence of extrinsic signals and is achieved by eliminating extracellular inhibitors of neuroectodermal fate and suppressing cell-cell signalling through limited cell density. Previous studies reported that ESC and ECC grown at low density and in absence of exogenous factors or feeder layers die within 24 h but acquire a neural identity as indicated by expression of the neural marker Nestin. Thus, this application is not suitable for generating neural cultures. Furthermore, it was reported that P19 cells survive and express neuroectodermal marker genes in serum-free DMEM/F12 medium containing transferrin, insulin, and selenite, although no neurites were identified.
Based on this background, in this study, a novel approach to induce neuronal differentiation in vitro was developed that implements a nutrient-poor environment, which, in contrast to previous studies, ensures the survival of neuronally differentiated cells over a long period of time and allows normal formation of neurites. Neither the formation of free-floating aggregates nor supplementation of growth factors or known inducers was required to establish a reliable neuronal differentiation protocol. A simple medium, consisting of DMEM/F12+N2 that was highly diluted in salt solution, was sufficient to drive a fast neuronal differentiation in monolayer cultures. Serum deprivation and strong dilution of DMEM/F12+N2 medium cause a nutrient-poor environment in which the influence of growth factors and inducers is minimized. This medium creates a metabolically defined environment that is presumably free of extrinsic signals that prevent the decision of neuronal fate. Analysis of the medium components discovered no actual inducer. Hence, it was suggested that the metabolic composition of the medium exclusively covers specific cell requirements of neurons, therefore ensures their survival, and drives the switch from pluripotent cells to neurons. The self-developed method was established by usage of the murine embryonal carcinoma cell line P19 and could be transferred to murine ESC. Consequently, the method could provide a feasible protocol for a generally valid neuronal default model.
The established protocol provides several advantages such as the possibility to generate stable pure neuronal cultures by a fast, simple, and highly reproducible one-step induction under defined medium conditions with a minimum of exogen effectors. The method is characterised by clear and steady medium conditions that makes the investigation of specific cell requirements during differentiation accessible. It is therefore expected to be a useful tool to investigate the molecular basis of neuronal differentiation as well as for high throughput screenings. The phenotype of mature postmitotic neurons was arising within one week and cultures were shown to stay stable at least for three weeks. The neuronal identity was confirmed by expression of neuronal markers through immunofluorescence staining and mass spectrometry analysis. Furthermore, increased levels of axon markers were detected in early neuronal differentiation and functionality of the synapses of the P19-derived neurons was ascertained by detection of calcium activity. Axonal laser ablation, immediately followed by fast regrowth of connections in the neuronal network, revealed a strong regeneration potential under the given conditions. Furthermore, the generated neurons showed a morphologically distinct phenotype and the formation of neural rosettes. Immunofluorescence staining demonstrated the generation of pure and homogeneous neuronal cultures, free of glial cells.
Retinoic acid (RA) plays an essential role in cell signalling during embryogenesis and efficiently induces neuronal differentiation in vitro in a concentration dependent manner. Neither retinol nor retinoic acid was included in any of the components of the self-prepared medium in this work. However, I observed, dependence on RARβ- and/or RARγ-regulated RA signalling in serum-free monolayer cultures. Nevertheless, neuronal differentiation in serum-free monolayer cultures was assumed to be RARα-independent because (i) RARα was slightly downregulated after neuronal induction, (ii) the truncated RARα of the RAC65 mutant had no effect on induction efficiency, and (iii) a pan-RAR inhibitor suppressed neuronal differentiation. In contrast to serum-free monolayer cultures, the truncated RARα prevented neuronal differentiation by application of the conventional protocol where cells are grown in free floating cell aggregates in serum-containing medium. Proteome analysis of P19 cells, treated by the self-developed differentiation protocol over five days showed increased levels of cellular RA binding proteins that mediate the cellular RA transport and are involved in canonical as well as non-canonical RA signalling.
...
Genetic engineering of Saccharomyces cerevisiae for improved cytosolic isobutanol biosynthesis
(2021)
The finite nature of fossil resources and the environmental problems caused by their excessive usage requires alternative approaches. The transformation from a fossil based economy to one based on renewable biomass is called a “bioeconomy”. To substitute fossil resources, various microorganisms have already been modified for the biosynthesis of valuable chemicals from biomass. However, the development of such efficient microorganisms at an industrial scale, remains a major challenge. The most prominent and robust microorganism for industrial production is the yeast Saccharomyces cerevisiae, which is known to produce ethanol that is used as renewable biofuel. However, S. cerevisiae is also naturally able to produce isobutanol in small amounts. Isobutanol is favoured as a biofuel compared to ethanol due to its higher octane number and lower hygroscopicity, which makes it more suitable for application in conventional combustion engines. In S. cerevisiae, the biosynthesis of isobutanol is permitted by the combination of mitochondrial valine synthesis (catalysed by Ilv2, Ilv5 and Ilv3) and its cytosolic degradation (catalysed by Aro10 and Adh2). The different compartmentalisation of the two pathways limit isobutanol biosynthesis. Thus, Brat et al. (2012) were able to increase the isobutanol yield up to 15 mg/gGlc by cytosolic re localisation of the enzymes Ilv2Δ54, Ilv5Δ48 and Ilv3Δ19 (cyt-ILV), with simultaneous deletion of ilv2. This corresponds to approximately 3.7% of the theoretical yield of 410 mg/gGlc, implying existing limitations in isobutanol biosynthesis, which have been investigated in this work.
For yet unknown reasons, isobutanol was only produced by S. cerevisiae in a valine free medium, according to Brat et al. (2012). This work shows that this can be attributed to the catalytic activity of Ilv2Δ54, which acted as growth inhibitor to S. cerevisiae. By this logic, a negative selection on the ILV2∆54 gene was exerted, which made the ilv2 deletion and simultaneous valine exclusion necessary to maintain the functional expression of toxic ILV2∆54. Furthermore, it was shown that valine exclusion is not mandatory due to the feedback regulation of Ilv2, permitted by Ilv6. Rather, increased isobutanol yield was observed when cytosolic Ilv6∆61 was expressed in the valine free medium, which is explained by the enhanced regulation of Ilv2Δ54 by Ilv6∆61 when BCAA are absent. Isobutanol biosynthesis is neither redox nor NAD(P)H co factor balanced. It was seen that co factor imbalance could be mitigated by the expression of an NADH oxidase (NOX), but not by expression of the NADH dependent ilvC6E6, since the latter showed low in vivo activity. Furthermore, it was seen that NAD(H) imbalance did already limit isobutanol biosynthesis, but the NADP(H) imbalance did not. Another limitation of cytosolic isobutanol biosynthesis is the secretion of the intermediate 2‑dihydroxyisovalerate, which then no longer is taken up by S. cerevisiae, causing a reduced isobutanol yield. This is attributed to insufficient Ilv3∆19 activity, due to poor iron sulphur cluster apo protein maturation. Therefore, it was aimed to replace Ilv3∆19 by heterologous dihydroxyacid dehydratases. Even though some of the enzymes were functionally expressed, none showed better in vivo activity than Ilv3∆19. Therefore, the Ilv3∆19 apo protein maturation was improved. This was achieved by the genomic deletion of fra2 or pim1 as well as by the cytosolic expression of Grx5∆29.
In addition to the isobutanol pathway, S. cerevisiae was optimised for isobutanol biosynthesis by rational and evolutionary engineering. For this purpose, the genes which are necessary for isobutanol production were integrated into the ilv2 locus, and the resulting strain was evolved in a medium containing the toxic amino acid analogue norvaline. Evolved single colonies were isolated, which presented improved growth and increased isobutanol yields (0.59 mg/gGlc) in a valine free medium, as compared to the initial strain. This is explained by a gene dosage effect which occurred during the evolutionary engineering experiment. In collaboration with Dr. Wess, the genes ilv2, bdh1/2, leu4/9, ecm31, ilv1, adh1, gpd1/2 and ald6 were cumulatively deleted in CEN.PK113 7D to block competing metabolic pathways. The resulting strain JWY23 achieved isobutanol yields up to 67.3 mg/gGlc, when expressing the cyt ILV enzymes from a multi copy vector. The most promising approaches of this work, namely the deletion of fra2 and the expression of Grx5∆29, Ilv6∆61, and NOX, were confirmed in this JWY23 strain. The highest isobutanol yield from this work was observed at 72 mg/gGlc for Ilv6∆61 and cyt ILV enzymes expressing JWY23, which corresponds to 17.6% of the theoretical isobutanol yield.
Isobutyric acid (IBA) is a by product of isobutanol biosynthesis, but it is also considered a valuable platform chemical. Therefore, the approaches that improved isobutanol biosynthesis were applied to the biosynthesis of IBA in S. cerevisiae. The highest IBA yield of 9.8 mg/gGlc was observed in a valine free medium by expression of cyt ILV enzymes, NOX and Ald6 in JWY04 (CEN.PK113 7D Δilv2; Δbdh1; Δbdh2; Δleu4; Δleu9; Δecm31; Δilv1). This corresponded to an 8.9 fold increase compared with the control and is, to our best knowledge, the highest IBA yield reported to date for S. cerevisiae.
Sleep is one of the fundamental requirements of all animals from nematodes to humans. It appears in different formats with shared features such as reduced muscle activities and reduced responsiveness to the environment. Despite the long history of sleep research, why a brain must be taken offline for a large portion of each day remains unknown. Moreover, sleep research focused on mammals and birds reveals two stages, rapid-eye-movement (REM) and slow-wave (SW) sleep, alternating during sleep. Whether these two stages of sleep exist in other vertebrates, particularly reptiles, is debated, as is the evolution of sleep in general.
Recordings from the brain of a lizard, the Australian bearded dragon Pogona vitticeps, indicate the presence of two electrophysiological states and provides a better picture of their sleep. Local field potential (LFP) signals, head velocity, eye movements, and heart rate during sleep match the pattern of REM and SW sleep in mammals. The SW and REM sleep patterns that we observed in lizards oscillated continuously for 6 to 10 hours with a period of 80-100 seconds when the ambient temperature was ~27°C. Lizard SW dynamics closely resemble those observed in rodent hippocampal CA1, yet originated from a brain area, the dorsal ventricular ridge (DVR), that does not correspond anatomically or transcriptomically to the mammalian hippocampus. This finding pushes back the probable evolution of these dynamics to the emergence of amniotes, at least 300 million years ago.
Unlike mammals and birds, REM and SW sleep in lizards occupy an almost equal amount of time during sleep. The clock-like alternation between these two sleep states was found initially by measuring the power modulation of two frequency bands, delta and beta. I recorded the full-band LFP and found an infra-slow oscillation (ISO) in the frequency range between 5 and 20 milli-Hz during sleep. The magnitude of ISO increased during sleep and decreased during both wakefulness and arousal during sleep. The up- and down-states of ISO were synchronized with the sleep state alternating rhythm but with a significant time lag dependent on the locations of the recording electrodes. Multi-site LFP recordings indicated that this ISO is a putative propagation wave sweeping extremely slowly, 30-67 µm/sec, from the posterior-dorsal pole to the anterior-ventral pole of the DVR.
Previous studies in other animals showed that brainstem areas such as the locus coeruleus, laterodorsal tegmentum, and periaqueductal gray are involved in sleep states regulation. It is sadly impossible to carry out in vivo recordings in the lizard brainstem without severely affecting them and their quality of life. I thus carried out ex vivo recordings in both DVR and brainstem. Pharmacological stimulation of the brainstem could reversibly silence one distinct EEG pattern characteristic of SW sleep, the sharp-wave and ripple complex, in DVR. An ISO could be recorded simultaneously in both DVR and brainstem. From data collected in both intact and split ex vivo brains, I concluded that there are independent ISO generators in at least two areas, the brainstem and the telencephalon. Their signals may normally be synchronized by long-range connections. The DVR ISO leads the brainstem ISO by ~29 sec. Optogenetic stimulation of brainstem neurons was able to disrupt the ISO in DVR reversibly.
In conclusion, the lizard brain offers a relatively simple model system to study sleep. Despite a diversity of results in different lizard species, my results revealed a number of new findings. Relevant for sleep research in general: 1) REM and SW sleep exist in a reptile. Since they also exist in birds and mammals, they probably existed in their common amniote ancestor, if not earlier. 2) REM and SW occupy equal amounts of time during sleep (50% duty cycle), a unique feature among all described sleep electrophysiological patterns, suggesting the possible existence of a simple central pattern generator of sleep, possibly ancestral. 3) I discovered the existence, in the local field potential, of an infra slow oscillation with extremely slow propagation, locked to the SW-REM alternating rhythm. The causes and mechanisms of this ISO remain to be understood. To my knowledge, the correlation between sleep states and a slow rhythm has only been reported in human scalp EEG recordings so far.
Protein ubiquitination is a post-translational modification that typically involves the conjugation of ubiquitin to substrate proteins via a three-enzyme cascade and regulates a wide variety of cellular processes. Recent studies have revealed that SidE family of Legionella effectors such as SdeA catalyzes novel phosphoribosyl-linked ubiquitination (PR-ubiquitination) of serines in host substrate proteins utilizing NAD+, without the need of E2, E3. The catalytic core of SdeA comprises a mono-ADP-ribosyltransferase (mART) domain that functions to ADP-ribosylate ubiquitin, and a phosphodiesterase (PDE) domain that processes ADP-ribosylated ubiquitin and transfers the resulting phosphoribosylated ubiquitin to serines of substrates.
To date, extensive efforts have been made to study the function of SdeA and mechanism of SdeA mediated PR-ubiquitination, however, the cellular effects of this novel ubiquitination and phosphoribosylation of ubiquitin remained poorly understood. In our study, using biochemical and cell biological approaches, we explored the biological effect of phosphoribosylation of ubiquitin caused by SdeA in cells. We found that phosphoribosylated ubiquitin is not available for conventional ubiquitination, thereby phosphoribosylation of ubiquitin impairs numerous classical ubiquitination related cellular processes including mitophagy, TNF-α signaling and proteasomal degradation.
The precise temporal regulation of the functions of bacterial effectors during Legionella infection by other effectors with antagonizing activities has been well studied so far. Not surprisingly, PR-ubiquitination catalyzed by SidE family effecters is tightly controlled as well, it has been long known that effector SidJ counteracts the toxicity of SdeA to yeast cells. Interestingly, in an experiment for verifying the activity of SidJ, we found that Legionella lysate lacking SidJ was still able to remove ubiquitin from PR-ubiquitinated substrates. Using biochemical approach we identified DupA and DupB, two Legionella bacterial effectors that specifically reverse the novel serine PR-ubiquitination catalyzed by SdeA. We found that DupA and DupB possess a highly homologous PDE domain that removes ubiquitin from PR-ubiquitinated substrates by cleaving the phosphodiester bond between the phosphoribosylated-ubiquitin and serines of substrates. Catalytically deficient mutant DupA H67A strongly binds to PR-ubiquitinated proteins but not capable of cleaving PR-ubiquitin, using it as a trapping bait we identified over 180 substrates of PR-ubiquitination, including a number of ER and Golgi proteins.
In particular, we found that exogenously expressed SdeA localizes to the Golgi apparatus via its C-terminal region and disrupts the Golgi. We validated the identified potential substrates of SidE effectors and found that SdeA modifies Golgi tethering proteins GRASP55 and GRASP65. Using mass spectrometry analyses we identified four serine targets (S3, S408, S409, S449) of GRASP55 PR-ubiquitinated by SdeA in vitro. Ubiquitination of GRASP55 serine mutant in cells co-expressing SdeA or infected with Legionella was markedly decreased, compared with that of the wild-type GRASP55. In addition, with co-immunoprecipitation analyses we found that SdeA-catalyzed ubiquitination regulates the function of GRASP55. PR-ubiquitinated GRASP55 exhibited reduced self-interaction compared to unmodified GRASP55, expression of GRASP55 serine mutant in cells in part rescued Golgi damage caused by SdeA. Furthermore, our study reveals that Golgi structure disruption caused by SdeA does not result in the recruitment of Golgi membranes to the Legionella-containing vacuoles. Instead, it affects cellular secretory pathway including cytokine secretion in cells.
Taken all together, this work expands the understanding of this unconventional PR-ubiquitination catalyzed by Legionella effectors and sheds light on the functions of PR-ubiquitination by which Legionella regulates the Golgi function and secretion pathway during bacterial infection.
Inducing cell death in tumor cells is a major goal of anti-cancer therapy. However, the preferable mode of cell death to induce is under debate. Apoptosis is known to be an anti-inflammatory and pro-resolving type of programmed cell death, whereas necroptosis results in the release of danger-associated molecular patterns (DAMPs) and is pro-inflammatory. Efferocytosis of apoptotic cells by macrophages results in a pro-resolving switch of macrophages polarization and is required to induce resolution of inflammation. This impact of apoptotic cells on macrophages is a non-desired consequence of cell death in tumors, which are often characterized by an overshooting wound healing response. Moreover, apoptosis resistance is frequently observed in cancer cells. To overcome apoptosis resistance in cancer cells, necroptosis can be induced as an alternative mechanism for cancer treatment. Interferons (IFNs) play an important role in tumor immune responses and act by inducing the expression of IFN-stiumlated genes (ISGs). Furthermore, IFNs were shown to be able to induce necroptosis together with Smac-mimetics when caspases are inhibited in different cancer cell lines. Necroptosis is induced by phosphorylation and activation of receptor-interacting serine/threonine-protein kinase 1 (RIPK1), RIPK3 and pseudokinase mixed lineage kinase domain-like (MLKL).
In my thesis, we first identified MLKL as an ISG in various cancer cell lines. MLKL upregulation was found to be a general feature of IFN signaling since both type I and type II IFNs increase the expression of MLKL. IFNy was able to upregulate MLKL at messenger ribonucleic acid (mRNA) and protein level indicating that MLKL is elevated transcriptionally. Indeed, Actinomycin D chase experiments showed that inhibition of transcription abolished MLKL upregulation upon IFN treatment. Both, knockdown of the IFNy-activated transcription factors interferon regulatory factor 1 (IRF1) and signal transducer and activator of transcription 1 (STAT1) as well as knockout of IRF1 significantly dampened MLKL mRNA upregulation, demonstrating that STAT1 and especially IRF1 are necessary to induce MLKL expression. This first part of the study highlights the upregulation of MLKL by IFNy as valuable tool to sensitize cells towards necroptosis and by that overcome apoptosis resistance in cancers.
When compared to apoptosis, the immune response to necroptotic cells and the polarization of macrophages phagocytosing necroptotic cells is not well studied. In most studies, cell death was induced by biological or chemical compounds, which may lead to artifacts by affecting the macrophages and triggering of unrelated signaling pathways. Therefore, in the second part of my thesis we used a pure cell death system of NIH 3T3 cells expressing either dimerizable caspase 8 or oligomerizable RIPK3 to induce cell death. Addition of B/B-Homodimerizer (dimerizer) to the cells resulted in apoptosis or necroptosis, which was confirmed by caspase 3/7 activation, phosphorylation of MLKL and inhibitor experiments, respectively. We analyzed the effect of dying cells on peritoneal macrophages by establishing a co-culture in a transwell system. The genetic profile of macrophages co-cultured with dying cells was evaluated by whole transcriptome RNA sequencing. In macrophages co-cultured with necroptotic cells genes corresponding to chemotaxis and hypoxia pathways were upregulated. A significant proportion of hypoxia-related pathways are mediated by hypoxia-inducible factor 1-alpha (HIF-1α), which also induces metabolic changes in polarized macrophages. We could show that macrophages co-cultured with necroptotic cells showed a decreased mitochondrial respiration, indicating an inflammatory (M1) polarization. Protein levels of chemokine C-X-C motif ligand 1 (CXCL1), which was increased in the RNA sequencing data, were also upregulated in supernatant of co-cultured macrophages and of necroptotic cells, demonstrating that necroptotic cells both secrete CXCL1 and induce gene expression of CXCL1 in peritoneal macrophages. This may influence the recruitment of neutrophils as inhibition of necroptosis during Zymosan-A-induced peritonits in mice decreased the levels of neutrophils at day 1 of this model of self-resolving inflammation.
Furthermore, RNA sequencing revealed an unexpected impact of apoptotic cells on macrophage biology as cell cycle and cell division pathways were increased. Enhanced proliferation of macrophages was confirmed by two functional assay with peritoneal macrophages isolated from mice and IC-21 macrophages. Inhibition of apoptosis during Zymosan-A-induced peritonits in mice demonstrated decreased mRNA levels of cell cycle mediators in peritoneal macrophages. Simultaneously with cell cycle activation, gene sets of prostaglandin E2 (PGE2) signaling were upregulated during RNA sequencing. In the second part of my thesis we could demonstrate, that apoptotic cells induce transcription of cell cycle genes and proliferation of macrophages and necroptotic cells are able to influence the chemokine profile of macrophages and thereby the recruitment of neutrophils.
Die Studien im Rahmen dieser Arbeit wurden am Modellorganismus Anabaena sp. PCC 7120 (Anabaena) durchgeführt, einem filamentösen Süßwasser-Cyanobakterium. Cyanobakterien sind photosynthetische, Gram-negative Organismen. Sie besitzen eine das Zytosol begrenzende Plasmamembran und eine Äußere Membran. TonB-abhängige Transporter (TBDTs) und Porine der Äußeren Membran bewerkstelligen und regulieren die Aufnahme von Nährstoffen. Typischerweise wenig abundante Substrate für den TBDT-vermittelten, aktiven Transport sind beispielsweise eisenhaltige Siderophore oder VitaminB12. Kleinere gelöste und abundante Stoffe wie Salze oder andere Ionen gelangen hingegen passiv durch Porine in das Periplasma.
In Anabaena wurden neun putative Porine identifiziert. Sieben hiervon wiesen eine porinspezifische Domänenstruktur auf (Alr0834, Alr2231, All4499, Alr4550, Alr4741, All5191 und All7614), und wurden im Rahmen dieser Arbeit näher betrachtet. Die Expression dieser sieben Gene wurde vergleichend untersucht, nachdem der Wildtyp in Standardmedium oder in Medium indem jeweils Mangan, Eisen, Kupfer oder Zink fehlte angezogen wurde. Außerdem wurde das Wachstum der einzelnen Porinmutanten im Vergleich zum Wildtyp auf Festmedium mit hohen Konzentrationen von Salzen, Antibiotika oder anderen Stoffen analysiert. Hierbei konnten den einzelnen Mutanten teilweise spezifische phänotypische Eigenschaften zugeschrieben werden. Zusammengefasst kann anhand der Analysenergebnisse vermutet werden, dass Alr4550 eine besondere Rolle in der Wahrung der Zellhüllenstabilität oder -integrität spielt, wohingegen das Fehlen von Alr5191 auf unbekannte Weise die Fixierung von Stickstoff zu erschweren scheint. Die alr2231-Mutante zeigte eine Resistenz gegenüber hohen Zinkkonzentrationen, was die Vermutung zulässt, dass Zink ein Substrat von Alr2231 darstellt. Für weitere Porine kann ebenfalls ein Zusammenhang zum Transport von Kupfer oder Mangan vermutet werden.
Neben Porinen wurden ebenfalls TonB-ähnliche Proteine in Anabaena untersucht. TonB ist ein plasmamembranständiges Protein, das in Komplex mit ExbB und ExbD die Energie für Transportprozesse über die Äußere Membran bereitstellt. Hierfür bindet TonB C-terminal an TBDTs und induziert dort Strukturänderungen, welche den Substratimport ins Periplasma ermöglichen. Als Energiequelle wird der Protonengradient genutzt, der über die Plasmamembran besteht. In Anabaena wurden vier putative TonB Proteine identifiziert, die sich jeweils in Länge und Domänenstruktur unterscheiden. Im Rahmen dieser Arbeit konnte durch Substrattransport-Experimente und Wachstumsanalysen gezeigt werden, dass TonB3 an der Aufnahme zweier Siderophore (Schizokinen und dem Xenosiderophor Ferrichrom) beteiligt ist, da die entsprechende Mutante sich als unfähig erwies diese zu als Eisenquelle nutzbar zu machen. Daneben wies TonB3 weitere Merkmale auf, die auch TonB-Proteinen anderer Organismen zugeschrieben wurden (Wachstumsdefizit der Mutante unter Eisenmangel, eisenabhängiges Expressionsprofil). Interessanterweise zeigte sich, dass das Siderophor Ferrichrom ebenfalls nicht als Eisenquelle für die tonB4-Mutante zur Verfügung stand, was zum Beispiel auf eine Beteiligung von TonB4 an dessen Transport hinweisen könnte.
TonB1, welches sich durch ein inkomplettes TBDT-Interaktionsmotiv auszeichnet, und TonB2 konnte keine Beteiligung am Siderophoretransport zugeschrieben werden, jedoch zeigten Mutanten der einzelnen Gene spezifische phänotypische Eigenschaften. Die tonB1-Mutante stach hervor durch ein vergleichsweise stark verzögertes Wachstum unter diazotrophen Bedingungen. Es konnte gezeigt werden, dass sowohl die Nitrogenaseaktivität als auch die expression vermindert war im tonB1-Mutantenstamm. Außerdem zeigten die Heterozysten dieser Mutante, die auf die Stickstoffixierung spezialisierten Zellen, eine abnormale Morphologie. Da die Expression von tonB1 jedoch nach dem Überführen von Wildypzellen in stickstoffreies Medium nicht erhöht war, kann eine direkte Beteiligung von TonB1 an der Heterozystendifferenzierung als unwahrscheinlich betrachtet werden. Die Zelleinschnürungen zwischen Heterozysten und vegetativen Zellen waren in I-tonB1 weniger ausgeprägt als im Wildtyp, was durch eine Anfärbung der Zellwand mit einem Fluoreszenzmarker gezeigt werden konnte. Ebenfalls konnte anhand des fluoreszierenden Markers Calcein gezeigt werden, dass die molekulare Diffusionsgeschwindigkeit zwischen Heterozysten und vegetativen Zellen, und auch zwischen zwei benachbarten vegetativen Zellen, in der tonB1-Mutante erhöht ist. Deswegen kann hier vermutlich vermehrt die Nitrogenase schädigender Sauerstoff in Heterozysten eindringen. Die aufgezählten Ergebnisse deuten auf eine Funktion von SjdR im Aufbau der Septumsstrukturen hin, beispielsweise durch Regulation der Peptidoglykansynthese oder -verteilung, weswegen TonB1 umbenannt wurde in SjdR (Septal junction disc regulator).
Die Untersuchung der tonB2-Mutante zeigte bei dieser eine veränderte Pigmentierung, eine vermehrte Lipopolysaccharidproduktion und Filamentaggregation sowie eine erhöhte Resistenz gegenüber bestimmten Antibiotika oder Detergenzien. Letzteres könnte auf die ebenfalls in der tonB2-Mutante beobachtete verringerte Porinexpression zurückgeführt werden. Es wurde außerdem eine vermehrte Anreicherung von Kupfer und Molybdän in der Mutante gemessen, was ein Grund für die Veränderte Pigmentierung sein könnte und ebenfalls die Porinexpression beeinflussen könnte. Insgesamt scheint sich das Fehlen von TonB2 auf die Integrität der Äußeren Membran auszuwirken. Daher kann für TonB2, eine Funktion in Anlehnung an das Tol-system vermutet werden.