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Strategies and mechanisms of Acanthamoeba predation
No full textAcanthamoeba is a genus of amoebae that commonly exists in the nature or human-related environments. To adapt to changing conditions in living environments, Acanthamoeba employs two typical life stages: a vegetative trophozoite stage for taking up nutrients and multiply, and a dormant cyst stage to overcome unfavourable conditions. Due to the
outstanding predatory capability of Acanthamoeba trophozoites on bacteria, fungi, or smaller protozoa, amoebae play a crucial role in the top-down control of microbial community, e.g. by eliminating 60% bacterial abundance in soil. Hitherto, it is known that Acanthamoeba spp. also act as protective shelters or even training grounds for many pathogenic bacteria, the so-called ‘amoeba-resistant bacteria’. Interactions between Acanthamoeba spp. and amoeba-resistant bacteria have been broadly investigated in the past decades, while the predation strategy of this powerful predator has been poorly studied so far. The current thesis spots light on a bacterial aggregation phenomenon called ‘backpack formation’ to better characterise and
understand the predation strategy of Acanthamoeba spp. on small prey such as bacteria. Backpack formation describes a bacterial aggregation phenomenon on the surface of Acanthamoeba spp. trophozoites. It was first observed during a previous study on the interaction between A. castellanii and Listeria monocytogenes, an opportunistic human
pathogen that shares environmental niches with protozoa. Backpacks usually form within minutes after exposing the bacteria to Acanthamoeba, always in the region of the amoebal uroid, which is an excretory organ of amoebal trophozoite. The short timeframe and specific location of the backpack led to the hypothesis that Acanthamoeba trophozoites actively recruit motile bacteria by releasing a chemical attractant. However, this hypothesis had not been
validated, and the underlying mechanism driving backpack formation remained unknown.
Therefore, the central focus of the thesis (i.e. Manuscript 1 and 2) was on elucidating the mechanisms behind backpack formation. By employing a microfluidic chemotaxis device, it was demonstrated that bacterial chemotaxis is not necessary to trigger the backpack
formation as previously hypothesised. Instead, backpack formation initiates from random encounters between bacteria and the amoebae. Upon successful capture, bacteria were first distributed evenly on the surface of Acanthamoeba trophozoites. Along with amoebal migration, the captured bacteria were assembled towards the rear of Acanthamoeba
trophozoites while forming backpacks. Further investigation of Acanthamoeba trophozoites' predation mechanism discovered that acanthopodia and nanofilaments are involved in the capture and adherence of prey, which are finally assembled into backpacks. Upon the observation that backpacks are formed with various food particles, including non-flagellated L. monocytogenes, Staphylococcus aureus cocci, and also abiotic latex beads, it became clear that backpack formation represents a general predation strategy of Acanthamoeba on small prey, regardless of prey morphology, motility, or surface sugar patterns. However, as the motility of bacteria increases the encounter rate, Acanthamoeba turns the table on motile bacteria as preferred prey. Overall, the backpack formation phenomenon can be summarised as an ‘encounter – capture – assemble’ driven process. This highly efficient predation strategy should not only be employed by Acanthamoeba trophozoites but by all eukaryotic cells showing a similar amoeboid migration behaviour.
Further investigation of the interaction between Acanthamoeba and bacteria was performed by plating-based association assays or antibiotic protection assays which are commonly applied to quantify the bacterial association rate or bacterial survival rate inside amoebal trophozoite. However, the analysis of the results from these assays disclosed their inherent drawbacks. The highly efficient phagocytosis and digestion of Acanthamoeba trophozoites make it very challenging to obtain a precise quantification result from these time-consuming assays. Consequently, an alternative method that combines flow cytometry as an enumeration technique with the application of a bacteriophage endolysin-derived fluorescent protein FPCBD was developed, which is presented in Manuscript 3. Upon short time labelling with FP� CBD, a clear differentiation is possible between the population of extracellular bacteria on the Acanthamoeba surface and the population of internalised bacteria, which can be detected
separately by flow cytometry. This method enables the targeting and thorough quantification of both bacterial populations in a single experiment. Meanwhile, it significantly reduces the duration of the analysis and minimises the inaccuracy caused by amoebal continuous
phagocytosis. The core design of this new approach is potentially applicable to a broader scenario for pathogen-host interactions
Human-Human Communication in Cyber Threat Situations
No full text. In cyber threat situations, decision-making processes within organiza� tions and between the affected organization and external entities are high-stake. They require human communication entailing technical complexity, time pressure, interdisciplinary factors, and often an insufficient information basis. Communi� cation in cyber threat situations can thus be challenging and has a variety of
implications for decision-making. The cyber-physical system is a rapidly chang� ing socio-technical system that is understudied in terms of how cyber events are communicated and acted upon to secure and maintain cyber resilience. The present study is the first to review human-to-human communication in cyber threat situa� tions. Our aims are to outline how human-human communication performance in cybersecurity settings have been studied, to uncover areas where there is poten� tial for developing common standards for information exchange in collaborative settings, and to provide guidance for future research efforts. The review was car� ried out according to the PRISMA guidelines and articles were searched for on scientific databases. Articles focusing on human-human communication in cyber threat situations published in peer reviewed journals or as conference papers were included. A total of 17 studies were included in the final review. Most of the studies were correlational and exploratory in nature. Very few studies characterize com� munication in useful goal-related terms. There is a need for more collaboration between cyber defense exercise-organizers and cognitive scientists. Future studies
should assess how team mental model-development affects team communication and performance in cyber defense exercises
Aufbau von Simulations- und Prognosemodellen energietechnischer Anlagen unter Einsatz von Deep Learning Verfahren
Get PDFDie vorliegende Arbeit untersucht am konkreten Beispiel einer Photovoltaikanlage die Generierung von Simulations- bzw. Prognosemodellen unter Anwendung algorithmischer Lösungsansätze der
Künstlichen Intelligenz und des Maschinellen Lernens, insbesondere des Deep Learning. Im Rahmen der Arbeit wird aufgezeigt und evaluiert, wie auf Grundlage realer Randbedingungen, etwa Wetterdaten des Deutschen
Wetterdienstes oder der geographische Standort einer Anlage, unter Einsatz von Deep Learning Ansätzen konkrete „personalisierte“ Modelle zur Berechnung der stündlichen Stromerzeugung der Anlage generiert
werden können. Modelle dieser Art bilden insbesondere im Kontext erneuerbarer Energien eine wichtige Grundlage für die Realisierung von Steuerungskonzepten und Betreiberstrategien in virtuellen Kraftwerten und leisten somit einen wichtigen Beitrag zum Gelingen der Energiewende
Real-time Base Excision Repair Assay to Measure the Activity of the 8-oxoguanine DNA Glycosylase 1 in Isolated Mitochondria of Human Skin Fibroblasts
Get PDF7,8-dihydro-8-oxoguanine (8-oxoG) is one of the most common and mutagenic oxidative DNA damages induced by reactive oxygen species (ROS). Since ROS is mainly produced in the inner membranes of the mitochondria, these organelles and especially the mitochondrial DNA (mtDNA) contained therein are particularly affected by this damage. Insufficient elimination of 8-oxoG can lead to mutations and thus to severe mitochondrial dysfunctions. To eliminate 8-oxoG, the human body uses the enzyme 8-oxoguanine DNA glycosylase 1 (OGG1), which is the main antagonist to oxidative damage to DNA. However, previous work suggests that the activity of the human OGG1 (hOGG1) decreases
with age, leading to an age-related accumulation of 8-oxoG. A better understanding of the exact mechanisms of hOGG1 could lead to the discovery of new targets and thus be of great importance for the development of preventive therapies. Because of this, we developed a real-time base excision repair assay with a specially designed double-stranded reporter oligonucleotides to measure the activity of hOGG1 in lysates of isolated mitochondria. This system presented here differs from the classical assays, in which an endpoint determination is performed via a denaturing acrylamide gel, by the possibility to
measure the hOGG1 activity in real-time. In addition, to determine the activity of each enzymatic step (N-glycosylase and AP-lyase activity) of this bifunctional enzyme, a melting curve analysis can also be
performed. After isolation of mitochondria from human fibroblasts using various centrifugation steps, they are lysed and then incubated with specially designed reporter oligonucleotides. The subsequent
measurement of hOGG1 activity is performed in a conventional real-time PCR system
Evaluation of humidity retention in refrigerator storage systems by application of a food simulant
No full textVegetables lose quality after harvest mainly due to water-related weight loss. In households, vegetables are usually stored in refrigerators, typically providing temperatures from 0 – 14°C and relative humidity ranges from 20 – 100 %. Weight loss is related to the storage humidity conditions. As a consequence, storage systems providing humidity-controlled conditions are decisive for the evaluation of the freshness performance of refrigerators. To evaluate the impact of storage zones on the fresh weight loss of stored goods, the international standard IEC 63169:2020 “Electrical household and similar cooling and freezing appliances – Food preservation” has been released. It uses a cellulose based food simulant, overcoming influences of cultivar and post-harvest handling conditions of real vegetables. This publication compares the weight loss of spinach and the food simulant in chilled storage conditions at three ranges of relative humidity. Different cultivars and pre-handling modifications of the spinach were used to determine the impact of product parameters on weight loss. A round robin test was performed to analyse the applicability of the IEC 63169:2020. The results prove the applicability of the standard to analyse the impact of humidity controlled storage on weight loss: It is shown that pre-handling has an impact on spinach's weight loss, which is overcome by the food simulant. For all tested conditions, the weight loss behaviour from spinach and the food simulant is correlating in test durations up to 72 h. The round robin test shows that the test method of IEC 63169:2020 provides repeatable and reproducible results
Verpacken von Fleisch und Fleischerzeugnissen im Kontext der aktuellen Nachhaltigkeitsdebatte
No full textInert Hydrophilic Particles Enhance the Terminal Properties and Structural Resilience of Meat Protein Gels during Heating
No full textMeat protein gels are present in a variety of foods and are frequently filled with fat particles. This study set out to elucidate the effect of replacing hydrophobic fat-based particles with hydrophilic inert glass particles on thermal and structural properties during heating. Meat protein gels were prepared with different diameters (60 to 90 mm) according to a typical emulsified sausage recipe and fat-based particles as well as inert glass particles were incorporated at concentrations from 10 to 40% and heated to 85 °C, while thermal as well as structural properties were monitored. The results revealed two main effects. First, due to the higher thermal conductivity, the lower heat capacity and the absence of extensive phase transitions, the time to reach the final temperature was reduced with increasing glass particle content (e.g. from 118 ± 2 min with 40% fat particles to 86 ± 1 min for gels with 40% glass particles at a depth of 40 mm). Second, volume change and temperature sweep measurements revealed that glass particles fostered the protein gel formation and enhanced the resilience against structural breakdown during heating. This was evident during small-amplitude shear experiments that showed an almost twofold increase in the storage modulus when 10% fat-based particles were replaced with 10% glass particles from G′85 °C = 223.4 ± 14.8 kPa to G′85 °C = 431.0 ± 16.6 kPa, respectively. Overall, these findings might be of interest to meat-product manufacturers that seek to lower heating times to reach the core temperature necessary for protein denaturation and ensure microbial safety with additional holding times and modify the structural properties of foods while replacing fat particles
An Approach to Accelerated Measurement of Dehydration (Freezer Burn) in Beef Patties in Household Freezers
Get PDFFreezer burn is a damage that occurs on the surface of frozen foods. To develop an accelerated method to measure the ability of different freezers to prevent freezer burn, the weight loss of beef patties, stored for 4 months in different freezers designed for household usage, is measured. These values act as a reference for accelerated tests (72 h instead of 4 months) with food simulants. Tests with wet cellulose sheets show a high correlation between experiments with foods and
simulants, which suggests the potential for the material used to be utilised in the future