Publication Server of Constructor University Library
Not a member yet
858 research outputs found
Sort by
Molecular and ecological analysis of cellular attachment and induction of transparent exopolymeric particle formation in diatom-bacteria interactions
No full textTransparent exopolymeric particles (TEP) and marine snow aggregates are vital components of the oceanic carbon cycle, leading to a substantial fraction of organic carbon sinking to depth or being provided for further recycling. Diatom-associated bacteria have been recently shown to directly impact TEP production and aggregate formation. However, very little is known about the molecular components that govern this interaction or the dynamics of TEP production and marine aggregate formation under changing environmental conditions. By combining molecular techniques and ecological experiments, we use an interdisciplinary approach to unveil hitherto unknown processes of diatom-bacteria interactions. As part of a collaborative and concerted effort, we initially established a genetically accessible bilateral model system consisting of the diatom Thalassiosira weissflogii and the marine gammaproteobacterium Marinobacter adhaerens HP15. Herein, we taxonomically established M. adhaerens HP15 as a novel member of the Marinobacter genus, revealed its genome sequence and established a genetic system to allow for the precise manipulation of this bacterium at the molecular level. In a second part, we used the established genetic toolbox to investigate the role of M. adhaerens HP15s motility during its interaction with the diatom. By generating M. adhaerens HP15 flagellum- and MSHA type IV pilus-deficient mutants, we demonstrate that a fullyfunctional flagellum is a pre-requisite for the bacterial attachment to both abiotic and diatom surfaces. We further show that the MSHA type-IV pilus is important for attachment, albeit to a lesser extent. Although both cellular appendages were shown to be crucial for attachment to diatom surfaces, this type of attachment was demonstrated to not be essential for inducing the formation of diatom-borne transparent exopolymeric particles (TEP). In the final part of this work, how TEP production dynamics and aggregate formation might be impacted in putative future oceanic scenarios was investigated. The results of our study suggest that the combined effect of ocean acidification and increased temperature might lead to a significant reduction in aggregate formation and sinking velocities of marine aggregates. We suggest that a combination of ocean acidification and global warming may severely impact the vertical transport of particulate organic matter in a future ocean
The Decoration Theorem of the Mandelbrot Set and Applications in Holomorphic Dynamics
No full textWe prove the decoration theorem of the Mandelbrot set M: if a homeomorphic copy of M (coming from renormalization) is removed from M, then most of the remaining connected components (the decorations of the little copy) are small. We prove that for every hyperbolic component of the Mandelbrot set, any two limbs with equal denominators are homeomorphic so that the homeomorphism preserves periods of hyperbolic components. This settles a conjecture on the Mandelbrot set that goes back to 1994. We give a topological description of the space of quadratic rational maps with superattractive two-cycles: its "non-escape locus" M2 (the analog of the Mandelbrot set M) is locally connected, it is the continuous image of M under a canonical map, and it can be described as M (minus the 1/2-limb), mated with the lamination of the basilica. The latter statement is a refined version of a conjecture of Ben Wittner, which in its original version requires local connectivity of M to even be stated. Our methods of mating with a lamination also apply to dynamical matings of certain non-locally connected Julia sets. Using the theory of iterated monodromy groups we construct the line complex for a linearizer map
An analysis of structural and biochemical aspects of the bacterial DNA adenine-N6 methyltransferase CcrM
No full textThe cell-cycle regulated methyltransferase (CcrM) specifically targets the N6 position of adenine residues within GANTC DNA target sequences. Its function is essential for the viability of several members of the α-class of the proteobacteria. In Caulobacter crescentus, CcrM plays a crucial role in the control of the cell division cycle by regulating the activity of the dnaA and ctrA genes, which, in turn, control a large number of genes with functions related to cell division and differentiation. While the biological function of CcrM has been well characterized, to date very little is known about its biochemistry. In this study, we have conducted a series of experiments meant to shed more light on the functional details of CcrM-catalyzed DNA methylation. We have established that CcrM methylates DNA in a distributive manner, correcting a pre-existing erroneous view, which held that CcrM was highly processive. Furthermore, through a combined bioinformatical and biochemical approach, we have found evidence of an indirect readout mechanism employed by CcrM in target sequence recognition. Several non-catalytic amino acid residues, when mutated to alanine, led to partial or complete loss of activity of the enzyme, suggesting a role in DNA recognition. In addition, we have identified a putative domain located at the CcrM C-terminus which is moderately conserved among methyltransferases targeting GANTC sequences, but is completely absent in others. If this C-terminal domain is removed, the truncated enzyme is no longer catalytically active. When separated, both the CcrM C-terminal domain and the N-terminal portion showed a weak DNA binding ability, which suggests that the C-terminal domain has a role in DNA binding, with the involvement of both the C- and N-terminal portions being needed for strong binding through a multidentate mechanism. Finally, scanning force microscopy data revealed the ability of CcrM to simultaneously bind two DNA molecules, which suggests intersegment transfer as a mechanism for target site localization in vivo
Screening tools for artificial electron transfer to P450 BM3
No full textCytochrome P450 monooxygenases catalyze a variety of reactions, but biotechnological approaches with isolated enzymes are still rare. One of the main challenges is their cofactor dependency hampering use in industrial processes. A promising possibility is the substitution of the cofactor by electrochemical means. For this strategy a technology is needed to parallelize electroenzymatic experiments and to accelerate research efforts. An electrochemical microtiter plate (eMTP), which is described in the first part of this work, enables parallelized electrochemical experiments with simultaneous optical data acquisition in up to eight wells of a microtiter plate. This is the first example for parallel spectroelectrochemistry in commercially available microtiter plates, wherein each well contains a set of independent electrodes. The well known redox probe potassium ferrocyanide and the mediator ABTS were characterized in the eMTP to proof the functionality and reliability of the system. Furthermore a mutant library of P450 BM3, a well studied fatty acid monooxygenase with high catalytic activity, was screened for its performance in the surrogate pNCA assay via the mediator cobalt sepulchrate. The eMTP was used to find optimized reaction conditions for the electroenzymatic process. The second part of the thesis focused on the conducting polymer polypyrrole. Due to its biocompatibility, conductivity and structural versatility polypyrrole provides all requirements needed for the efficient immobilization and electrochemical actuation of redox molecules at electrodes. Direct electron transfer between redox enzymes and electrodes is of high interest, since it represents an approach for heterogeneous process design with integrated enzyme retention and simultaneous control of the redox state of the enzymés active site. Pyrrole and two carboxylic acid modified derivatives were introduced as flexible immobilization matrices. A set of redox active iron compounds and small heme type redox proteins was screened towards improved direct electron transfer via the conducting polymer matrix. Based on the commercially available monomers several immobilization methods were employed, which were in addition applied to P450 BM3
Burnout and Performance in Organizations An Investigation of the Interplay of Individual and Job Characteristics
No full textThis dissertation examined under which conditions stressful working conditions relate to emotional exhaustion and how emotional exhaustion affects individual performance. Emotional exhaustion, which refers to a depletion of emotional resources, is considered to be the core component of burnout. Burnout has become an important issue for individuals at work and their organizations. Therefore, interest in this concept from researchers and practitioners has increased dramatically over the past twenty years. Despite knowing that stressful job conditions are potential antecedents of emotional exhaustion, we know much less about factors that can alter this relationship as well as about consequences of emotional exhaustion. This dissertation addressed this gap in three empirical studies, which are summarized below. The first study tested whether matching and non-matching resources buffer detrimental effects of job demands on emotional exhaustion. The second study examined whether a person characteristic (overcommitment) aggravates effects of stressful working conditions on emotional exhaustion and job performance. The third study investigated if emotional exhaustion relates to cognitive performance and job performance. Study 1 investigated whether interaction effects between job demands and resources on emotional exhaustion are more likely if these three concepts’ dimensions match (emotional, cognitive or physical). I tested the Demand-Induced Strain Compensation (DISC) model’s proposition that matching resources are more likely to buffer job demands’ detrimental effects on job strain, such as emotional exhaustion, than non-matching resources. I retrieved data from 177 school teachers; a subsample was re-examined after a time lag of about 21 months (N= 56). Unlike previous DISC studies, I tested the interaction between demands and resources with at least two demands per dimension, increasing the reliability of my findings. Focusing on the dimensions of demands and resources and their match introduces a new theoretical approach to research on teacher burnout. The present study contributes to the literature by testing the DISC model with a longitudinal design in a sample of German school teachers, including a statistical test of the triple-match hypothesis. Linear regression analyses revealed concurrent and lagged main and interaction effects of emotional and cognitive job demands and resources on emotional exhaustion. In large parts, job demands were positively and resources were negatively related to emotional exhaustion. Moreover, resources buffered detrimental effects of job demands. Results mainly supported the propositions of the DISC model which provides a valuable theoretical framework for the study of interaction effects in occupational health psychology and, in particular, for interventions to reduce job strain in teachers. Because reducing job demands is not always feasible, I propose that interventions should also target improving teachers’ resources (e.g., emotional support) in order to reduce emotional exhaustion among teachers. Such interventions would likely benefit from considering the dimension of working conditions and outcomes by focusing on matching concepts. Study 2 focused on the often neglected interaction hypothesis of the model of Effort-Reward Imbalance with its two components effort-reward imbalance (ERI) and overcommitment (OC), which proposes that OC potentiates the detrimental relationships between ERI and the outcomes, here emotional exhaustion and job performance. ERI represents an imbalance between work-related costs (in the model termed efforts) and occupational gains (in the model termed rewards). Overcommitted employees are characterized by a motivational pattern of excessive work-related commitment and a high need for approval. They have difficulties to withdraw from work and are disproportionally irritable. I applied multilevel modeling based on data from 152 employees nested in 20 teams from a German manufacturing company. As predicted, results showed that ERI was positively related to emotional exhaustion and negatively related to supervisor-rated job performance while OC was unrelated to emotional exhaustion and job performance. Thereby, Study 2 extends the scope of the ERI model by being the first study that relates ERI to supervisor-rated job performance as an organizational outcome. Importantly, testing the interaction hypothesis by taking OC into account as a moderator, results showed that OC significantly aggravated the associations between ERI and emotional exhaustion as well as between ERI and job performance. Especially for overly committed employees, balanced working conditions appear to be important to prevent emotional exhaustion and to avoid performance decrements. Therefore, it seems crucial to identify these employees and take special care of them, for example, by offering trainings to alter their work-related attitudes of approval and commitment. Study 3 investigated how emotional exhaustion, as a state of depleted resources and compromised executive control, relates to cognitive performance, job performance, and health. Theoretically, I assumed that executive control deficits impair cognitive performance. I further assumed that exhausted employees are less likely to invest their remaining resources and thus show lower job performance. Because emotional exhaustion evolves gradually, I focused on working and apparently healthy teachers reporting various levels of exhaustion. Unlike most previous studies, I applied a longitudinal design, which offers more insight into the direction of effects. The combination of longitudinal data, multiple-source data, and the assessment of various individual performance facets collected in a non-clinical sample make a novel study that contributes to the literature of burnout and cognitive performance. As hypothesized, cross-sectional linear regression analyses of 100 teachers showed that emotional exhaustion was significantly negatively related to cognitive performance, indicated by self- and peer-rated cognitive impairments as well as performance decrements in a neuropsychological learning and memory test (all p < .05). Longitudinal linear regression analyses confirmed this for self- and peer-rated cognitive impairments by trend (p < .10). In these longitudinal linear regression analyses, work-related exhaustion also significantly predicted self-rated physical health. However, emotional exhaustion did not affect self-rated job performance, which might be explained with the compensatory control model. In tests of reversed causation, none of the outcome variables at Time 1 predicted change in emotional exhaustion at Time 2. This speaks against cognitive impairments serving as a vulnerability factor for exhaustion. In sum, findings contribute to the understanding of the burnout syndrome. Results underpin the negative consequences of emotional exhaustion for cognitive performance and health that are relevant for individuals and organizations alike. To sum up, this dissertation extended research on work-related emotional exhaustion and individual performance. More specifically, interaction hypotheses were tested within a recently developed and an established theoretical job strain model—the DISC model and the ERI model, respectively. Additional variables were integrated in the models, such as conflicts with colleagues and emotional support in the DISC model or job performance in the ERI model, and thus extended their scopes. Moreover, consequences of emotional exhaustion for cognitive performance were examined. Methodologically, longitudinal and multilevel study designs as well as supervisor- and peer-ratings as well as laboratory test data add to the current state of research. Taken together, results presented in this work showed that protective resources and vulnerability factors moderate relationships between stressful working conditions and emotional exhaustion and should be taken into account when thinking about work place interventions. Finally, this work underpins the relevance of emotional exhaustion for individual functioning with the finding that emotional exhaustion can impair cognitive performance and health
Segmentation of Stochastic Images using Stochastic Partial Differential Equations
No full textThe task of segmentation, the separation of an image into foreground and background, is typically performed on noisy images, and it is a great challenge to get satisfactory results. The noise in the images depends on the acquisition modality, the acquisition parameters, and extrinsic parameters. The acquisition step is a physical measurement and has to be equipped with information about the measurement error. This quantification of the measurement error is typically omitted in image processing. Neglecting the error leads to a loss of information about the influence of the input error to the result of the image processing steps. A possibility to model the image noise is to perceive a pixel inside the image as a random variable. These images are called stochastic images. Applying segmentation methods based on partial differential equations (PDEs) on stochastic images leads to stochastic PDEs (SPDEs). In this thesis, the focus is on intrusive methods for the discretization of SPDEs, because classical sampling strategies are time-consuming. The approximation of random variables uses the Wiener-Askey polynomial chaos and the discretization of the SPDEs uses the generalized spectral decomposition and finite difference schemes for random variables. This thesis investigates random walker segmentation, Ambrosio-Tortorelli segmentation and level set based segmentation methods for stochastic extensions. Furthermore, a sensitivity analysis of the classical segmentation approaches uses the stochastic framework by making segmentation parameters random variables. The result of the presented work is a framework carrying the probability distribution of the stochastic gray values, i.e. the random variables, through all steps of the segmentation pipeline. This yields segmentation results containing, for each pixel, a probability of belonging to the object. Furthermore, this stochastic segmentation identifies regions where the image noise has an important impact on the segmentation result
The Development of Novel Antibiotics Using Chemical Evolution
No full textOver the past few decades, bacterial resistance against antibiotics has emerged as a real threat to human health. Both mutation and most importantly the rapid exchange in genetic information between bacteria have resulted in multidrug resistant strains. A statement of the world health organization (WHO) predicts that by year 2020, 30% of all bacterial infections will not be successfully treated because of resistance. Accordingly, there is an urgent demand to develop innovative approaches for discovering new antibiotics. In an attempt to provide such approach, a novel class of chiral non-racemic macrocycles has been synthesized in [2+2]-cyclocondensation reactions of chiral dioxolane dihydrazides obtained from commercially available tartaric acids with aromatic dialdehydes. The novel macrocycles were named tetra-carbohydrazide cyclophanes and can be readily available in both enantiomeric forms (R or S). Three macrocycles underwent successfully dynamic exchange to generate a small dynamic combinatorial library (DCL) of eight members. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF/MS) and tandem MS showed potential recognition of a one member from the generated DCL to AcNH-L-Lys- D-Ala-D-Ala-Gly-COOH oligopeptide which mimics bacterial cell wall structure. Reactions of dioxolane dihydrazides with aromatic diiso- and isocyanates afforded novel classes of tetra-(hydrazinecarboxamide) cyclophanes and bis-N-substituted hydrazinecarboxamide receptors, which also showed potential recognition to a wide selection of chiral carboxylic acids and oligopeptides as confirmed by ESI-TOF/MS
Primary Amine Containing Bifunctional Catalysts for Asymmetric Aldol and Mannich Reactions
No full textThe synthesis of enantiomerically pure compounds is one of the major areas of organic chemistry, with emphasis on the elaboration of commodity chemicals into advanced high value enantiopure building blocks. Organocatalysis, when small chiral organic molecules catalyze product formation, is a relatively new field, which has grown explosively and become a main focus of research. In the past 5 years chiral primary amine derivatives, usually based on naturally occurring cinchonine alkaloids, have been successfully shown for asymmetric aldol, Michael, and Mannich reactions. The results have been impressive but substrate classes remain untested or are still challenging. To overcome these limitations, modular catalyst designs based on new template will be required. To address this problem, we have designed two types of catalysts: 1) primary-tertiary diamine (picolylamines) and 2) assembled based catalysts. Our chiral primary-tertiary diamine catalyst is good for aldol reactions, while the self-assembled catalyst was found to be superior for asymmetric Mannich reactions. Both of these catalyst categories operative via in situ chiral enamine, enolate equivalents, which then trap electrophiles to give the desired products
Thermodynamic and Fluorescence-based Investigations of Host-Dye Reporter Pairs for Sensing of Biological Analytes
No full textThis doctoral thesis describes the development of supramolecular sensing ensembles, based on host-dye reporter pairs, for the sensing of biological analytes and monitoring enzymatic transformations. The rational design and selection of host-dye pairs are governed by the size-fit relationship and the favourable photophysical changes, exhibited by the dye upon complexation. The binding constants of the reporter pairs are examined by isothermal titration calorimetry (ITC), which reveals the thermodynamic forces of binding (Ka, delta H, and T delta S). Fluorescence-based techniques are used to study the photophysical characteristics of the dyes upon host complexation. The reporter pairs with pronounced fluorescence differentiation upon binding are selected for further sensing applications of biological analytes. The reporter pairs are used for the sensing of different types of analytes such as various amino acids, including lysine and its methylated derivatives, as well as choline-type of neurotransmitters. The analytes are further implemented in the development of supramolecular tandem assays for monitoring enzymatic activity. The design of tandem assays employs the differential binding affinity of the analysed substrates and products to the selected macrocyclic host. On the basis of the choline studies, a novel type of tandem assay for acetylcholinesterase has been developed. Due to the similar binding of the substrate (acetylcholine) and the product (choline) to the macrocycle of choice, the enzyme is coupled together with choline oxidase, which further converts choline to betaine (a weaker competitor). This constitutes a new tandem assay type, which works in an "enzyme-coupled-substrate-selective" mode. The determination of enzyme-kinetic parameters, the quantification of absolute choline and acetylcholine concentrations, and the screening for inhibitors for Alzheimer's disease is easily achieved with the novel assay
The Value of Cultural Values Reinvestigating the Relationship Between Culture-Level Values and Individual-Level Psychological Phenomena
No full textCulture is a complex and multi-dimensional construct that is difficult to grasp. It refers to a complex system of (material and non-material) elements that are shared by the members of a social collective, which in turn is most often determined by national boundaries, ethnicity, religion, or geographical concentration. In literature, culture has been understood as resulting from an adaptive interaction between humans and the environment. It is learned by its people and transmitted across generations and therefore relatively stable over time. This thesis is about culture. In particular, it is about cultural values which have been viewed by many cultural researchers as core features of culture. Cultural values represent the implicitly and explicitly shared abstract ideas about what is good, right and desirable in a society (Schwartz, 1999). They reflect what has been agreed upon to be a functional response to challenges that a society faces. These implicit or explicit fundamental agreements or ideals find expressions in poetry and art, communication, child-rearing and other everyday practices, but also in societal institutions such as educational, economic or judicial systems. Cultural values shape individuals’ thoughts, feelings and actions. They serve as a reference frame for individuals regarding what the world is like, how it should be, and what kind of behavior is appropriate. Individuals use these guiding principles as reference for evaluating their thoughts, feelings, and behavior. In this thesis, the relationship between cultural values and individual’s thinking, feelings and behavior is (re-)investigated. The main proposition of the thesis is that not all individuals living in a particular culture are guided by its values to the same extent, and that particular assumptions can be made regarding who is more guided than the other. Three general research hypotheses are tested. The first takes a developmental psychological perspective by focusing on adolescents. It is hypothesized that the relationship between a cultural group’s values and its members’ thoughts, feelings, and actions is stronger among older than among younger adolescents. The former have more likely gone through a period of identity exploration during which they have elaborated the personal meaning of their cultural group membership, have more likely committed to the cultural group’s values and are thus more likely to be guided by them. The second and third hypotheses regard to the role of migratory background and cultural minority status, respectively, as a moderator of the link between a culture’s values and the thinking, feelings and behavior of the individuals living in that culture. Immigrant and non-immigrant cultural minorities are not only exposed to the cultural values of the society’s cultural majority but in addition to cultural values prevalent in their cultural minority community. These potentially compete with the cultural majority’s values, which is why the latter are less likely to be adopted by cultural minority members as strongly as by cultural majority members. Hypothesis 2 states that the relationship between a cultural group’s values and its individuals’ thinking, feeling, and behavior is weaker among immigrants living in that group than among non-immigrants, which regards especially to first- as compared to second-generation immigrants and those coming from a culturally more distant compared to those from a culturally closer region. Hypothesis 3 also relates to cultural value adoption in the context of migration and cultural minorities but pursues a different approach: It states that immigrant- and non-immigrant cultural minority members differ in their similarity to the cultural values of their country’s majority (cultural value fit) depending on their acculturation orientations (integration, marginalization, assimilation, and separation). The cultural value fit is expected be highest among individuals pursuing an assimilation orientation, and lowest among those pursuing a separation orientation. The hypotheses are investigated using the cultural value model introduced by Shalom Schwartz – the thesis’ recurrent theme – which has so far only insufficiently been used with regard to these questions. Schwartz proposed that cultures can be aligned along three cultural value dimensions. Each dimension provides two opposing answers to a particular basic issue a society is confronted with when regulating human activity. The first dimension is constituted by egalitarianism at one pole and hierarchy at the other pole, the second dimension differentiates between cultures that value autonomy versus those valuing embeddedness, and the third dimension distinguishes between harmony versus mastery. Each hypothesis is tested in a separate study. Hypothesis 1 is investigated in study 1 with six samples of cultural majority and minority adolescents. Hierarchical linear models and ANOVA-based trend analyses are performed using Schwartz’s cultural value dimensions as the group-level variables and individuals’ group-related attitudes as an exemplary individual-level psychological variable. Results confirm the age-related hypothesis for the culture-level value dimension egalitarianism-hierarchy. Regarding the other two dimensions relationships with individuals’ group-related attitudes are evident but not significantly stronger in the older compared to the younger age group. In general, the results indicate that the hypothesis can be confirmed only with regard to the cultural value dimension egalitarianism-hierarchy, whose content is most relevant for the explanation of group-related attitudes. Hypothesis 2 is investigated in study 2 with data from 24 representative country-samples from Round 4 of the European Social Survey. Again, hierarchical linear models are performed using Schwartz’s culture-level value dimensions as group (country)-level variables, and group-related attitudes as an exemplary individual-level variable. In addition, migratory background is included as an individual-level variable, and cross-level interactions with cultural values are examined. The hypothesis is confirmed showing that the relationship between all three cultural value dimensions and group-related attitudes is weaker among immigrants than non-immigrants, especially among first-generation immigrants and those from a culturally more distant region. The results for the harmony-mastery dimension, however, show a somewhat different pattern than the other two dimensions. Hypothesis 3 is investigated in study 3 with the same data of immigrant and cultural minority adolescents used in study 1. The results confirm the hypothesis: Immigrant and cultural minority adolescents with an assimilation orientation show a stronger cultural value fit to the country’s cultural majority compared to those with a separation orientation. The unexpected, though interesting finding is that this result pattern was much more evident among Former Soviet Union immigrants (diaspora immigrants) as compared to Turkish immigrants in Germany and Arab Israelis. The three studies provide new insights that can potentially stimulate further research. Each study is therefore re-evaluated in an appertaining discussion section and additionally in a general discussion at the end of the thesis. Implications for future research are derived based on each study’s findings. Furthermore, a number of additional moderators and ideas that are worth investigating in future studies are outlined. Finally, regarding each study, and regarding the general approach of the thesis, a number of content-related and methodological aspects that have received some debate in literature are critically addressed