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Modification and Evaluation of PAN and PP Membranes with Polymer Brushes via UV-induced Graft Polymerization
Get PDFBiofouling is a major problem for membrane filtration because it blocks the pores of the membrane and significantly decreases flux. This work developed a mild and modular method to functionalize the surfaces of polyacrylonitrile (PAN) ultrafiltration membranes for water purification and polypropylene (PP) nonwoven membranes for air filtration. The goal was to reduce biofouling by introducing zwitterions and quaternary ammonium compounds (QACs)
Modified Cost-Risk Analysis as a Bridge Between Target-Based and Trade-Off-Based Decision-Making Frameworks
Get PDFAnthropogenic climate change creates a decision-making problem between near-term mitigation costs and long-term risks of severe impacts. Traditional frameworks such as cost-benefit analysis (CBA) and cost-effectiveness analysis (CEA) represent two ends of a spectrum: the former trades off mitigation costs against expected damages, while the latter seeks the least-cost path to meet climate targets, assuming damages cannot be reliably quantified. Cost-risk analysis (CRA) emerged to reconcile CEA’s temperature objectives with utility-based flexibility; however, improved damage quantification calls for a more integrated approach. This thesis develops Cost-Benefit-Risk Analysis (CBRA)—a novel framework that integrates explicit (partial) damage estimates into a reduced-weight risk function for temperature targets, bridging target-based and trade-off-based methods.
The thesis first examines the carbon budget concept, which posits a near-linear relationship between cumulative emissions and global temperature rise (TCRE)—a key condition for CRA–CEA equivalence. Scenario-dependent deviations are analyzed using an optimization program, demonstrating maximal deviations of less than 10\% of total temperature rise, which rapidly diminish thereafter. Using FaIRv2 and a one-box model, it is shown that scenario dependence can be explained by the shape of the pulse response, interpreted as Green’s function. This approach generalizes to models of any complexity and helps characterize nonlinearity in the carbon budget.
Combined with projections for agriculture and mortality, and implemented in the CGE model GTAP-INT 2, the results reveal substantial regional disparities and significant global damages, particularly in poorer, populous regions—with long-term GDP reductions of up to 50\% for certain countries, while a few specific regions may experience marginal GDP gains (less than 1\%) under high-emission scenarios.
Finally, CBRA is implemented within the MIND-L integrated assessment model, incorporating hereby modified FaIR climate module with probabilistic climate sensitivity and a partial damage function derived from CGE-informed economic damages. It confirms that, under a carbon budget-consistent module, CRA and CEA yield equivalent outcomes. Moreover, we show that, by calibrating the CBRA framework to meet the predefined temperature target, one can assess how much of the unknown risks embodied in the climate target are explicitly quantified by the implemented damage function. These findings position CBRA as a consistent, flexible tool for climate policy design
Dissecting the dynamics of cell death pathways in Hirschsprung's Disease: A comparative analysis of viable and non-viable cells under proinflammatory conditions
Get PDFBackground:Hirschsprung’s disease (HSCR) is a congenital disorder of the enteric nervous system that predisposes patients to severe inflammatory complications, such as Hirschsprung-associated enterocolitis (HAEC). Method:In this study, we employed a novel flow cytometry-based assay to investigate the dynamics of cell death in colonic organoids from HSCR patients and matched controls subjected to acute and chronic inflammatory stimuli. Main Result:Using this approach, we quantified three distinct types of programmed cell death — RIPK1-dependent apoptosis, RIPK1-independent apoptosis, and necroptosis—in both viable and non-viable cells. Our data revealed that HSCR organoids exhibited a significantly increased susceptibility to acute inflammation, with elevated rates of cell death compared to controls. In contrast, chronic stimulation induced a regulatory shift from RIPK1-dependent to RIPK1-independent apoptosis, particularly in non-viable HSCR cells.These results, derived from patient-specific organoid models, provide insight into the epithelial stress response in HSCR. Conclusion:These findings suggest altered inflammatory signaling in HSCR and highlight the central role of RIPK1 in regulating epithelial cell fate, and may guide the development of targeted therapeutic strategies for preventing HAEC in patients
with HSCR.Unsere Studie zeigt, wie organ-spezifisch Organoide bei Morbus Hirschsprung (HSCR) auf akute und chronische Entzündungsreize reagieren. Dabei konnten wir mittels eines neu etablierten FACS-basierten Assays unterschiedliche Formen des programmierten Zelltods (RIPK1-abhängige und -unabhängige Apoptose sowie Nekroptose) in lebenden und toten Zellen identifizieren und analysieren. Unter akuter Stimulation zeigten HSCR-Organoide eine erhöhte Zellsterblichkeit im Vergleich zu Kontrollen. Bei chronischer Stimulation kam es zu einer Verschiebung der Zelltodmechanismen: Während die RIPK1-abhängige Apoptose abnahm, nahmen alternative Signalwege – insbesondere RIPK1-unabhängige – zu. Diese dynamische Umstellung lässt auf eine adaptive, jedoch gestörte epithelial immunologische Antwort schließen. RIPK1 fungiert dabei als zentraler Regulator zwischen immunologisch stiller Apoptose und entzündungsfördernder Nekroptose. Die Ergebnisse unterstreichen die Bedeutung dieses Signalwegs im epithelialen Stressverhalten und liefern neue Hinweise auf krankheitsspezifische Besonderheiten bei HSCR. Diese Erkenntnisse könnten dazu beitragen, pathologische Entzündungsreaktionen bei HSCR besser zu verstehen und neue therapeutische Ansätze zur Prävention von HAEC zu entwickeln
The Astrophysical Search For Axion Like Particle Signatures In γ-ray Propagation
No full textThe work undertaken during this Doctoral period involved studying interactions of Very High Energy (VHE) γ-rays with Astrophysical magnetic fields and the Extra-galactic Background Light (EBL). The primary goal was to search for signatures of ultralight Axion Like Particles (ALPs) via their interactions with VHE γ-rays. These particles are also a promising Dark Matter candidate.
Our first project attempted to find spectral “wiggles” induced by photon-ALP oscillations in the presence of Astrophysical magnetic fields. Our candidate VHE γ-ray source was the Messier 87 Active Galactic Nucleus, located at z ∼ 0.0042 at the center of the Virgo cluster. We chose to implement a Gaussian turbulence model for the Virgo cluster magnetic field as a radially varying function dependent on the electron density profile. Electron density measurements and calculations of Faraday Rotation measures from M87 and M84 were applied to constrain the model parameters, giving us a central magnetic field value of B0 = 34.2 µG. We modeled spectral wiggles as outcomes of various pseudo-randomized magnetic field realizations along the line of sight. We performed Likelihood ratio tests and other statistical analyses to verify any preferences for our models, fitting the pseudo-random models against data from H.E.S.S. observational campaigns. We chose observations from 2005, 2010 and 2018 when the source was reported to have been observed in flaring/high states. Our results were statistically inconclusive, showing at best only a preference of < 2σ for the ALPs case. Strictly speculatively, this may hint at a possible signal region within our parameter space. Reports of the magnetic field model and constraints, along with the ALP search were presented and published as proceedings at the Heidelberg International Symposium 2022 and at ICRC 2023 respectively.
Beyond our ALP searches, we were also able to make contributions toward the fields of EBL research and γ-ray Astronomy. We made a first-ever detection of intrinsic curvature in the VHE γ-ray spectrum of the AGN hosted by Messier 87 during flares. We detected such a spectral curvature in with a confidence of ∼ 4σ. In a combined analysis with colleagues from the H.E.S.S. Collaboration, we were able to utilize the same data set to place upper limits on the normalization term of three EBL models which are widely used in the field of γ-ray Astrophysics. The discovery of curvature, along with the EBL model constraints were published as a peer reviewed collaboration paper in the Astronomy & Astrophysics Journal in 2024.
Another project during the research period searched for ALP induced upturns in the VHE spectra of γ-ray sources. We searched for, and attempted to relate spectral upturns to ALP induced transparency of the Universe to VHE γ-rays. We model the upturns as outcomes of pseudo randomized realizations of the intergalactic and galactic magnetic fields along the line of sight. We fit these models against our data set and performed Likelihood ratio tests. We see at best one limiting case where the ALPs model can be ruled out at ∼ 4σ. We constructed an elaborate and robust dataset consisting of observations of our 13 candidate blazars, all of which have been observed in flaring states during H.E.S.S. observational campaigns. The data set was analyzed and temporally segmented where any source exhibited significant variability in its emission pattern with respect to its observed flux and spectral hardness. The data set has potential application for various types of Astrophysics research and will be made publicly available after publication of our results. This effort is being undertaken by colleagues
Selected applications of resonant phenomena in fourth-generation light sources
No full textThis thesis is focused on the design of the future fourth-generation light source PETRA IV and its booster ring. It investigates the utilization of linear and non-linear resonant phenomena to shape and control the electron beam—a subject that has traditionally played a secondary role in beam dynamics studies of electron storage rings, but becomes more important in the last generation of synchrotron light sources. The main research topic is to develop techniques to mitigate detrimental side effects of the unprecedented ultra-low emittances for storage rings
expected at PETRA IV. At extremely low emittances, the electron beam exhibits significantly reduced transverse dimensions, leading to increased charge density, which translates into increased probability of Coulomb interactions between electrons inside the bunch. These ultimately lead to beam quality and lifetime degradation. A promising approach to mitigating these adverse effects is to shape the beam such that the transverse emittances are equalized.
This thesis evaluates three mechanisms for the generation of transverse emittance control: vertical dispersion waves, AC dipole excitation and emittance sharing— thereby leveraging resonant phenomena to reshape the beam properties in the last two cases. Among these, the exploitation of the difference resonance ( − = 0) to induce emittance sharing is identified as the most favorable approach, owing to its straightforward operational implementation and well-established theoretical foundation. The impact on beam dynamics performance with a beam with equal emittances is evaluated with numerical simulations. The key findings are:
first, the Touschek limited beam lifetime increases by a factor of two. Second, intra-beam scattering-induced emittance deterioration is reduced, allowing the emittance to remain below 20 pm rad even for high single-bunch currents up to = 2.5 mA.
Furthermore, PETRA IV features a sufficiently large dynamic aperture to support off-axis injection for both charge top-up and initial filling. Consequently, the injection efficiency under machine operation at the coupling resonance is assessed. Simulation results indicate that the strong amplitude dependence introduced by nonlinear effects in the electron dynamics enables an injection efficiency exceeding 99%. Experimental studies are conducted at the PETRA III electron storage ring at DESY and the Extremely Brilliant Source (EBS) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The experimental results reveal for both machines an injection efficiency below 20%, which deviates significantly from both simulation predictions (>99%) and a previously reported value in the literature (≈70%) at the Standford Positron Electron Accelerating Ring (SPEAR) in California, USA.
This discrepancy underscores the necessity for dedicated optimization campaigns targeting nonlinear beam dynamics to achieve acceptable off-axis injection efficiency. Furthermore, it highlights the need for continuous refinement of existing models to accurately describe high-amplitude electron dynamics, particularly in the presence of strong nonlinear elements.
Additionally, an unexpected resonant phenomenon is encountered during the course of this thesis. Namely, the generation of quasi-stable transverse resonance islands is observed during PETRA IV simulation campaigns. Although these islands emerge when the machine is operated near the coupling resonance, no direct correlation with the vertical tune setting is found. Instead, dedicated simulations reveal that their formation is attributed to strongamplitude detuning induced by nonlinear elements, which are introduced to mitigate the impact of nonlinear aberrations in the electron beam optics. More specifically, the amplitude detuning drives the horizontal tune to cross the third-order resonance for off-axis injected particles, making this resonance crossing the primary mechanism responsible for the formation of the islands. To validate and further characterize these quasi-stable resonance islands, dedicated experimental campaigns are conducted at the ESRF-EBS electron storage ring. The experimental results reveal a lifetime =6.74 s ±(0.23 stat. + 0.03 sys. ) s of trapped particles in the resonance islands. This study represents the first observed instance of a nonlinear resonant phenomenon being triggered while the machine’s working point is found far from the nominally excited resonance. The full potential of these resonance islands remains an open question for future research, which will focus on further characterization and strategies to enhance electron capture lifetime.
Finally, a resonant slow extraction scheme that makes use of the generation of third order resonance islands is proposed. This novel variation of the resonant extraction can deliver extraction efficiencies in excess of 90% with electrostatic septa already available at other research facilities. The concept has been evaluated in the context of the future booster ring DESY IV and can potentially serve the high energy physics community that primarly exploits the beams offered at DESY in the test beam facility
Numerically Efficient Theoretical Frameworks for Collective Spontaneous Emission
No full textCooperative spontaneous emission, or superradiance, occurs when a group of excited atoms emit light coherently in an intense burst due to synchronized dipole moments. This phenomenon is significant for applications in spectroscopy, metrology, and high-brightness light sources. Modeling such collective emission is challenging for large atomic systems, prompting the development of efficient numerical frameworks. This dissertation introduces a second-quantized formalism in Liouville space and a stochastic approach based on the positive P-representation. These methods are applied to study compact systems of multi-level emitters under incoherent pumping and decoherence. Numerical results benchmark the two approaches and highlight their utility and limitations for simulating many-body quantum effects
Vorhersage seismischer Wellenfelder mit Encoder-Decoder-Netzen: vom Lernen von Übertragungsfunktionen zu virtuellen seismischen Arrays
No full textThe prediction of seismic wave fields between stations using machine learning offers great potential for geophysical monitoring, particularly in remote areas or in regions with sparse sensor coverage. This thesis introduces a novel encoder-decoder deep learning architecture that successfully learns the transfer function between seismic stations. By learning the complex signal transformations, this method enables accurate predictions of how seismic signals alter as they travel from one station to another. Notably, high quality predictions are achieved using only two days of data consisting solely of ambient seismic noise. The method’s robustness in a range of scenarios is demonstrated via validation at a seismic exploration site with a variety of noise sources. The network shows particular strength in capturing phase-related features, which is crucial to its performance in seismic wave prediction. A systematic parameter study reveals important insight about the variables affecting model performance and points out areas for future development.
Virtual Seismic Arrays are introduced as a powerful proof of concept, extending the approach from individual station pairs to entire seismic arrays. By training the algorithm on all station pairs within an array, a set of predictive models is obtained that collectively form the Virtual Seismic Array. This enables the reconstruction of full-array recordings from a single reference station, even after physical sensors are no longer present. In the secondary microseism frequency band, beamforming analysis validates the effectiveness of Virtual Seismic Arrays by showing a high degree of agreement between the original and predicted waveforms.
This novel application of encoder-decoder networks for modelling transfer functions has the potential to enhance seismic monitoring, while reducing the need for continuous sensor coverage. By reconstructing signals at multiple stations from a single reference station, the approach enables ongoing array functionality in remote regions while reducing costs and maintaining array capabilities. These improvements are beneficial in industries like advanced seismic instrumentation and ultra-precision manufacturing where even small vibrations have significant impact on results. This is particularly beneficial in projects like the Einstein telescope, where the sensitivity of gravitational wave detections depends on reducing seismic disturbances
Polarimetrie von laser-plasma-beschleunigten Elektronenstrahlen
No full textLaser Plasma Acceleration (LPA) with its extremely high gradients promises compact accelerators and great progress has been made in that direction. However, many applications in nuclear and high energy physics require polarised electron beams. The motivation of the LEAP project at DESY is the first time demonstration of LPA with polarisation. This thesis focuses on the design and commissioning of a Compton transmission polarimeter to verify electron polarisation in future LEAP experiments.
The polarimeter makes use of the production of circularly polarised bremsstrahlung during the passage of the electrons through a suitable target. The photon polarisation is then measured with the aid of the transmission asymmetry related to the magnetisation direction of an iron absorber.
A Monte Carlo design study revealed that a dedicated bremsstrahlung converter target had little impact on the asymmetry and was therefore omitted from the final design. Furthermore, resolving the small anticipated asymmetries (∼ 1.5 ‰) within a feasible number of shots requires an energy resolution better than 2 % for the calorimeter detecting the transmitted photons. Consequently, a homogeneous lead-glass calorimeter was constructed.The LEAP polarimeter was commissioned using an unpolarised electron beam. It was found to perform as designed; however, the measurements were dominated by systematic uncertainties due to false asymmetries arising from fluctuations in beam charge and energy. The analysing power of the polarimeter was determined to be 11.74 ± 0.18 %.Laser-Plasma-Beschleunigung (LPB) bietet mit ihren extrem hohen Gradienten das Potenzial für sehr kompakte Beschleuniger, und in diesem Bereich wurden bereits erhebliche Fortschritte erzielt. Allerdings erfordern viele Anwendungen in der Kern- Hochenergiephysik polarisierte Elektronenstrahlen. Das LEAP-Projekt am DESY zielt darauf ab, erstmals die Erzeugung polarisierter Elektronenstrahlen mittels LPB zu demonstrieren. Diese Arbeit konzentriert sich auf die Entwicklung und Inbetriebnahme eines Compton-Transmissionspolarimeters zur Verifizierung der Elektronenpolarisation in zukünftigen LEAP-Experimenten.
Das Polarimeter nutzt die Erzeugung zirkular polarisierter Bremsstrahlung während der Passage von Elektronen durch ein geeignetes Target. Die resultierende Photonenpolarisation wird durch Messung der Transmissionsasymmetrie in Abhängigkeit von der Magnetisierungsrichtung eines Eisenabsorbers bestimmt.
Eine Monte-Carlo-Designstudie ergab, dass ein spezielles Bremsstrahlungskonverter-Target nur einen geringen Einfluss auf die Asymmetrie hat. Es wurde daher in der finalen Konstruktion weggelassen. Darüber hinaus erfordert die Auflösung der sehr kleinen zu erwartenden Asymmetrien (∼ 1.5 ‰) innerhalb einer realistischen Anzahl von Messungen eine Energieauflösung von besser als 2 % für das Kalorimeter, das die transmittierten Photonen detektiert. Daher wurde ein homogenes Bleiglas-Kalorimeter konstruiert.
Das LEAP-Polarimeter wurde mit einem unpolarisierten Elektronenstrahl in Betrieb genommen. Es zeigte sich, dass das Polarimeter wie vorgesehen funktioniert, jedoch werden die aktuellen Messungen durch systematische Unsicherheiten dominiert, die durch falsche Asymmetrien aufgrund von Fluktuationen in der Strahlladung und -energie verursacht werden. Die bestimmte Analysierstärke des Polarimeters hat einen Wert von 11.74 ± 0.18 %
Discovering the Potential of Microalgae-Bacterial Consortia for New Strategies in Fighting off Bacterial Biofilms
No full textBacterial biofilms are comparable to organs complex structures that provide protection and nutrition to their inhabitants. The biofilm matrix shields embedded bacteria by trapping antibiotics, toxins and agents of the host immune system at the surface while inside the biofilm bacteria enhance their endurance through genetic exchange, physiological heterogeneity and metabolic reduction. Due to their highly resilient character, biofilms cause severe and costly problems in industry, farming and health care, with this study focusing particularly on challenges of the fast-growing sector of aquaculture. Facing the limited number of available antibiotics and in contrast the constantly growing antibiotic resistance in bacteria, new strategies are inevitable to address pathogenic bacteria and their sheltering surrounding.
Microalgae are small, unicellular organisms that successfully inhabit all kinds of aquatic environments displaying a worldwide distribution. Their cooperative lifestyle with beneficial bacteria shelters their survival in challenging environments and protects them efficaciously from pathogenic threads. Up to date little is known about the composition and the intrinsic potential of these microalgae-bacterial consortia. Hence, the present study focused on the potential of microalgae-bacterial consortia to influence biofilm formation of pathogenic bacteria. This question was addressed by data mining of newly established metagenomes and by practical application. First approaches made use of the total supernatant of various microalgae cultures to find out if there is any effect on bacterial biofilms proved by static anti-biofilm assay and, as effects were measurable, which microalgae’s supernatant showed the highest inhibiting effect in terms of biofilm reduction. Of 17 marine and freshwater microalgae cultures (data not entirely shown) the six candidates with the highest inhibitory results on bacterial biofilms of Pseudomonas aeruginosa PA14, Burkholderia cenocepatia K56-2, Stenotrophomonas maltophilia K279a, Stenotrophomonas maltophilia SM454 and Klebsiella pneumonie WT1617 were chosen for further investigation. The supernatant of the marine microalgae Tetraselmis chui reduced biofilm in all tested bacteria significantly by an average of 57.2%. Biofilm inhibition, if only for certain bacterial species each, was also observed for the supernatants of the marine microalgae Nannochloropsis salina, Isochrysis galbana and Isochrysis spec. as well as for the freshwater microalgae Chlorella vulgaris, and Scenedesmus acuminatus. The inhibitory potential of the total supernatants of microalgae cultures on the biofilm of P. aeruginosa PA14 was explored more deeply by laser scanning confocal microscopy (LSCM). Calculations of total cell numbers within a defined biofilm area revealed a decrease of 25% of P. aeruginosa cells after treatment with T. chui supernatant and alterations in biofilm architecture towards lower biofilm density.
Metagenomes of the six effective microalgae were prepared to first enlighten the phylogeny of the bacterial communities encompassing the individual microalgae and second to elucidate their enzymatic potential. Though all of the microalgae-bacterial consortia showed a prevalent fraction of proteobacteria with an emphasis on alphaproteobacteria, particularly apparent in T. chui, I. galbana and C. vulgaris, the composition of the consortia on genus level occurred highly divers. Only the marine bacteria Roseobacter, Roseovarius, Muricauda and Marinobacter appeared repeatedly within the metagenomes. Promising enzyme classes were explored and quantified for current and future use. Since bacterial biofilms promote virulence and decrease antibiotic susceptibility a multifaceted approach seems to be required to either alter the biofilm architecture for better access of classic antibiotics to the embedded pathogens or to weaken and ideally inhibit the process of biofilm formation. Hence, the metagenome data of the six microalgae-bacterial consortia should serve as a valuable toolbox for advances to interfere with key points in biofilm formation such as quorum sensing, initial attachment or accumulation of EPS (extracellular polymeric substances) with special regard to the role of extracellular DNA. First experiences with a microalgae-metagenome-derived enzyme were gained with a putative quorum quenching dienelactone hydrolase (Dlh3). Due to its intended application in aquaculture, Dlh3 was administered to the fish pathogens Edwardsiella anguillarum, Aeromonas salmonicida, P. aeruginosa, Flavobacterium columnare and Flavobacterium psychrophilum. Interactions of Dlh3 and the fish pathogens were analyzed in static anti-biofilm assays, LSCM, and oCelloScope, revealing decreased biofilm formation, e.g., for E. anguillarum of up to 54.4% in static anti-biofilm assay and alterations in biofilm construction in optical approaches. Encouraged by these impressions more target-specific enzymes were chosen from the newly prepared metagenome data of microalgae-bacterial consortia. The successfully overexpressed enzymes, a methylcytosine-specific restriction endonuclease, that cleaves DNA in a specific, modified context, an 8-oxoguanine deaminase, that alters external DNA and a second dienelactone hydrolase were characterized by phylogenetic and structural attributes. First applications of the enzymes on fish pathogens, analyzed by LSCM, had considerable effects on the viability and structure of the observed biofilms. Considering the harmlessness of the enzymes stated in toxicity assays, this study might be a path-breaking approach for a versatile attack on pathogenic biofilms to avoid bacterial adaptation and resistance to antibiotic treatment and simultaneously, by harboring a wide-range enzymatic toolbox, maintaining the flexibility to react to changing demands e.g. in the context of high-density farming as for aquaculture.Bakterielle Biofilme weisen vergleichbar mit Organen komplexe Strukturen auf, die den innewohnenden Bakterien Schutz und Nahrung gewähren. Die Biofilm Matrix schützt die Bakterien im Biofilm indem sie Antibiotika und Angriffe des Wirts‘ eigenen Immunsystems abfängt, während die Bakterien im Biofilm ihre Lebensfähigkeit durch genetischen Austausch, physiologische Heterogenität und Reduzierung des metabolischen Umsatzes steigern. Durch ihren starken protektiven Charakter verursachen Biofilme große Schäden und hohe Kosten in Industrie, Tierzucht und im Gesundheitswesen. Ein besonderes Augenmerk legt diese Studie auf die Herausforderungen im schnell wachsenden Sektor der Aquakultur. Im Bewusstsein der begrenzten Verfügbarkeit von und der stetig wachsenden Resistenz gegen die angewandten Antibiotika, ist es unerlässlich, neue Strategien gegen krankheitserregende Bakterien und ihre schützende Umgebung zu entwickeln.
Mikroalgen sind kleine, einzellige Organismen, die mit ihrer weltweiten Ausbreitung erfolgreich alle Arten von aquatischen Lebensräumen bewohnen. Die Kooperation mit Bakterien sichert ihr Überleben in herausfordernden Lebensräumen und schützt sie weitgehend vor Pathogenen. Über die Zusammensetzung der Mikroalgen-Bakterien-Gemeinschaften ist bisher wenig bekannt. Diese Studie untersucht daher eingehend das Potential von Mikroalgen-Bakterien-Gemeinschaften, Einfluss auf die Bildung von Biofilmen pathogener Bakterien zu nehmen. Dafür wurden Daten von neu etablierten Mikroalgen-Metagenomen analysiert und verschiedene praktische Anwendungen erprobt. Zunächst wurde der komplette Überstand von Mikroalgenkulturen genutzt um festzustellen, ob ein Effekt auf die Biofilmbildung pathogener Bakterien in einem statischen Anti-Biofilm-Assay messbar wäre, und welche Mikroalgenkulturen die stärkste biofilmreduzierende Wirkung erzielten. Von 17 getesteten marinen und Süßwasser Mikroalgenkulturen (Daten nicht vollständig dargestellt) wurden die
sechs Kulturen mit der stärksten inhibitorischen Wirkung auf die Biofilme der Bakterien Pseudomonas aeruginosa PA14, Burkholderia cenocepatia K56-2, Stenotrophomonas maltophilia K279a, S. maltophilia SM454 und Klebsiella pneumonie WT1617 für weitere Untersuchungen ausgewählt. Der Überstand der Mikroalge Tetraselmis chui, zeigte eine biofilmreduzierende Wirkung auf alle getesteten Bakterien mit einer durchschnittlichen Verminderung um 57.2%. Biofilminhibition, wenn auch jeweils nur für einzelne Pathogene, zeigten darüber hinaus die marinen Mikroalgen Nannochloropsis salina, Isochrysis galbana und Isochrysis spec. sowie die Süßwasser Mikroalgen Chlorella vulgaris und Scenedesmus acuminatus. Das inhibitorische Potential der kompletten Überstände von Mikroalgenkulturen auf den Biofilm von P. aeruginosa PA14 wurde tiefergehend mittels Laser scanning confocal microscopy (LSCM) ermittelt. Eine 25%ige Reduktion der absoluten Zellzahlen innerhalb eines definierten Bereichs eines P. aeruginosa Biofilms konnte nach Zugabe des Überstands der Mikroalge T. chui berechnet werden. Gleichzeitig veränderte sich die Architektur des P. aeruginosa Biofilms in Richtung einer geringeren Dichte.
Von den sechs wirkungsvollen Mikroalgen wurden Metagenome angefertigt, um die Phylogenie der kooperierenden Bakterien zu ergründen, sowie Einblicke in das enzymatische Potential der Mikroalgen-Bakterien-Gemeinschaften zu gewinnen. Trotzdem sich in allen Metagenomen ein hoher Anteil an Proteobakterien, vor allem Alpha Proteobakterien zeigte, insbesondere bei T. chui, I. galbana und C. vulgaris, herrschte auf Genus-Level hohe Diversität. Einzig die marinen Bakterien Roseobacter, Roseovarius, Muricauda and Marinobacter waren in mehreren Metagenomen nachweisbar. Des Weiteren wurden mögliche wirkungsvolle Enzyme in den Metagenomdaten für aktuelle und zukünftige Anwendungen klassifiziert und quantifiziert. Da Biofilme bakterielle Virulenz verstärken und die Empfindlichkeit gegenüber antibakteriellen Substanzen verringern scheint nur ein breitgefächerter Ansatz erfolgsversprechend, um entweder die Biofilmarchitektur aufzubrechen und klassischen Antibiotika den Zugang zu den Bakterien zu erleichtern oder um den Prozess der Biofilmformation zu schwächen, im besten Falle sogar zu unterbinden. Die Metagenomdaten sollten daher als Werkzeugkasten dienen, Schlüsselstellen in der Biofilmbildung wie das Quorum Sensing, die initiale Anheftung oder die Anreicherung von EPS (extracellular polymeric substances) anzugreifen. Ein besonderes Augenmerk sollte auf die Rolle der extrazellulären DNA gerichtet werden. Erste Erfahrungen mit einem Enzym, das auf Grundlage eines Mikroalgenmetagenoms entwickelt wurde, konnten mit einer Dienlacton Hydrolase (Dlh3) gewonnen werden, die
wahrscheinlich im Sinne des Quorum Quenchings wirkt. Im Hinblick auf deren Anwendbarkeit im Aquakultur-Sektor wurde Dlh3 an den Fischpathogenen Edwardsiella anguillarum, Aeromonas salmonicida, P. aeruginosa, Flavobacterium columnare und Flavobacterium psychrophilum erprobt. Die Wirkung der Dlh3 auf die Fischpathogene wurde in statischen Anti-Biofilm-Assays, LSCM und dem oCelloScope getestet. Um bis zu 54.4% konnte die Biofilmbildung z.B. in E. anguillarum reduziert werden, einhergehend mit Veränderungen der Biofilmarchitektur, die in den optischen Verfahren deutlich wurden. Ermutigt durch die gewonnenen Erkenntnisse, wurden weitere zielgerichtete Enzyme in den neu etablierten Metagenomdaten der Mikroalgen-Bakterien-Gemeinschaften gesucht. Die erfolgreich überexprimierten Enzyme, eine Methylcytosin-spezifische Restriktionsendonuclease, die DNA an spezifisch modifizierten Basen schneidet, eine 8-Oxoguanin Deaminase, die extrazelluläre DNA modifiziert und eine zweite Dienlacton Hydrolase wurden phylogenetisch und strukturell charakterisiert. Erste Anwendungen der Enzyme auf Fischpathogenen zeigten deutliche Effekte auf die Überlebensfähigkeit der bakteriellen Zellen im Biofilm und auf die Strukturen der Biofilme im LSCM. In Anbetracht der Unschädlichkeit der untersuchten Enzyme für eukaryotische Zellen, die in Toxizitätstests bewiesen wurde, könnte diese Studie ein wegweisender Ansatz für einen vielfältigen Angriff auf bakterielle Biofilme sein, der die Gefahr der Resistenz vermindert und gleichzeitig, durch den Charakter eines variablen Werkzeugkastens die Flexibilität erhält, auf wechselnde Bedürfnisse zu reagieren, wie sie in Tierzucht mit hoher Dichte, wie der Aquakultur, zu erwarten sind