In addition to occasional opportunistic colonization of the oral mucosa, Candida albicans is frequently found in carious dentin. The yeast’s potential to induce dental caries as a consequence of its pronounced ability to produce and tolerate acids was investigated. Eighty caries-active Osborne-Mendel rats were raised on an ampicillin-supplemented diet and exposed to C. albicans and/or Streptococcus mutans, except for controls. Throughout the 28-day test period, the animals were offered the modified cariogenic diet 2000a, containing 40% various sugars. Subsequently, maxillary molars were scored for plaque extent. After dissection, the mandibular molars were evaluated for smooth surface and fissure caries. Test animals exposed to C. albicans displayed considerably more advanced fissure lesions (p < 0.001) than non-exposed controls. While S. mutans yielded similar results, a combined association of C. albicans and S. mutans had no effect on occlusal caries incidence. Substituting dietary sucrose by glucose did not modify caries induction by C. albicans. However, animals fed a diet containing 20% of both sugars showed no differences to non-infected controls. Smooth surface caries was not generated by the yeast. This study provides experimental evidence that C. albicans is capable of causing occlusal caries in rats at a high rate. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Correct layering (lamination) of neurons in the central nervous system (CNS) is critical for the tissue functionality. Neuronal lamination is established during development, when the majority of neurons have to move from their birthplace to the appropriate layer, where they function. Therefore, to grasp the logic of CNS development, it is essential to understand the kinetics and modes of the variety of neuronal translocation events. Most of our knowledge about neuronal translocation has been gained using fixed tissue or ex vivo imaging, which is not ideal for such a dynamic process heavily dependent on the surrounding environment. To avoid these limitations, I combined translucent zebrafish embryos with light sheet fluorescence microscopy, which together enabled gentle in toto imaging of neuronal translocation. I studied the translocation of retinal ganglion cells (RGCs) across the developing zebrafish retina. RGCs are the first neurons that differentiate in the vertebrate retina and are born in a proliferative zone at the retinal apical side. From here, they move basally, spanning the complete apico-basal length of the tissue. They are destined to occupy the most basal layer, where their axons form the optic nerve. Although it was described that RGCs move their soma while being attached to both apical and basal sides of the retina, the kinetics and cell biological mechanisms of somal translocation remained unknown. Extracting single cell behavior of RGCs from high-resolution movies of their translocation allowed for quantitative analysis of RGC movement. I revealed that RGCs cross the retina in less than two hours in a directionally persistent manner. The movement of RGC soma is a cell autonomously generated process, which requires intact microtubules and actin-dependent basal attachment of cells for speed and efficiency. Unexpectedly, interference with somal translocation leads to a shift towards a multipolar migratory mode, previously not observed for RGCs, in which they temporarily lose both apical and basal attachment and apico-basal polarity. The multipolar mode is overall slower and less directionally persistent, but still allows RGCs to reach the basal retina. However, when RGC translocation is inhibited completely, they differentiate ectopically in the center of the retina, which in turn triggers the formation of ectopic layers of later born neurons. These results highlight the importance of establishing the basal layer of ganglion cells for ensuing retinal lamination. Overall, I generated important advances in the understanding of neuronal translocation and lamination, which might be relevant for other parts of the CNS.

The microtubular cytoskeleton is a ubiquitous and highly diverse biopolymer network present in all eukaryotic cells. Microtubules stochastically alternate between phases of growth and shrinkage. Cells take advantage of this dynamicity to generate forces for essential processes, such as cell division, motility or morphogenesis. Regulating the microtubule dynamics enables cells to adaptively respond to a wide range of tasks and conditions. Molecular mechanisms underpinning the regulation are not fully understood. Using a bottom-up approach and the combination of single molecule total internal reflection fluorescence (TIRF) microscopy and interference reflection microscopy (IRM), we here reconstituted and explored two dynamic cytoskeletal systems. (i) Microtubule doublets, comprising incomplete B-microtubule on the surface of a complete A- microtubule, provide an essential structural scaffold for flagella. Despite the fundamental role of microtubule doublets, the molecular mechanism governing their formation is unknown. We here demonstrate an inhibitory role of tubulin C-terminus in microtubule doublet assembly. By partial enzymatic digestion of polymerized microtubules followed by the addition of free tubulin in the presence of a stabilizing agent, we assembled microtubule doublets and revealed the B-...

Failure analysis and optimization of semiconducting devices request knowledge of their electrical properties. To meet the demands of today’s semiconductor industry, an electrical nanometrology technique is required which provides quantitative information about the doping profile and which enables scans with a lateral resolution in the sub-10 nm range. In the presented work it is shown that Kelvin probe force microscopy (KPFM) is a very promising electrical nanometrology technique to face this challenge. The technical and physical aspects of KPFM measurements on semiconductors required for the correct interpretation of the detected KPFM bias are discussed. A new KPFM model is developed which enables the quantitative correlation between the probed KPFM bias and the dopant concentration in the investigated semiconducting sample. Quantitative dopant profiling by means of the new KPFM model is demonstrated by the example of differently structured, n- and p-type doped silicon. Additionally, the transport of charge carriers during KPFM measurements, in particular in the presence of intrinsic electric fields due to vertical and horizontal pn junctions as well as due to surface space charge regions, is discussed. Detailed investigations show that transport of charge carriers in the semiconducting sample is a crucial aspect and has to be taken into account when aiming for a quantitative evaluation of the probed KPFM bias.

Neurogenesis is the process of generation of neurons during embryonic development and adulthood. The focus of this doctoral work is the study of the cell biological aspects of neurogenesis and the mechanisms regulating the switch of neural stem cells from proliferation to differentiation. During embryonic development neurogenic divisions occur at the apical or basal side of the pseudostratified epithelium that forms the wall of the neural tube, the neuroepithelium. Apical asymmetric neurogenic divisions (AP) give rise to a neuron and a progenitor cell, while basal symmetric neurogenic divisions (BP) give rise to two neurons. The first part of this thesis is focused on the study of some cell biological aspects of BPs. We first validated the use of the Tis21-GFP knock in mouse line, previously generated in our laboratory. We found that the totality of neurogenic progenitors is marked by the expression of a nuclear GFP. We calculated the abundance of BPs overtime since the onset of neurogenesis showing that BPs overcome APs over development. We studied the loss of apical contact of the basal dividing cells. We found that both neurogenic and non-neurogenic basally dividing progenitors miss the apical contact; which is lost prior mitosis. We generated and characterized a second mouse line, the Tubb3-GFP line expressing a plasma membrane-localized GFP in neurons. These two lines were crossed to obtain a new line (TisTubb-GFP) allowing detection of neurogenic divisions and tracking daughter cells. Using this model: (i) we imaged symmetric neurogenic divisions of BPs, identifying daughter cells as neurons, during imaging; (ii) we compared the kinetics of betaIII-tubulin-GFP appearance after apical or basal mitosis, showing that daughters of BPs express betaIII-tubulin-GFP faster than daughters coming from apical divisions; (iii) we imaged neuronal migration and localization of the Golgi apparatus. Neurogenesis in the adult is confined to two specific regions in the telencephalon: the sub ependymal zone, lining the ventricle, and dentate gyrus of the hippocampus. The second part of this thesis focuses on the adult neurogenic progenitors lineage. Tis21-GFP expression was found and characterized in the two adult neurogenic regions from early postnatal to adulthood. Using a panel of markers for the adult neurogenic cell lineage and confocal imaging, we characterized Tis21-GFP expression, in the dentate gyrus. Tis21-GFP is first expressed in the neurogenic subpopulation of doublecortin positive cells. Tis21-GFP is inherited by the neurons and eventually degraded. Moreover, our data suggest that mitotic Tis21-GFP cells are an indicator of the levels of neurogenesis more accurate than doublecortin positive cells, in the early postnatal mouse. (Anlage Quick time movies 77,88 MB)

Near-field optical microscopy has attracted remarkable attention, as it is the only technique that allows the investigation of local optical properties with a resolution far below the diffraction limit. Especially, the scattering-type near-field optical microscopy allows the nondestructive examination of surfaces without restrictions to the applicable wavelengths. However, its usability is limited by the availability of appropriate light sources. In the context of this work, this limit was overcome by the development of a scattering-type near-field microscope that uses a widely tunable free-electron laser as primary light source. In the theoretical part, it is shown that an optical near-field contrast can be expected when materials with different dielectric functions are combined. It is derived that these differences yield different scattering cross-sections for the coupled system of the probe and the sample. Those cross-sections define the strength of the near-field signal that can be measured for different materials. Hence, an optical contrast can be expected, when different scattering cross-sections are probed. This principle also applies to vertically stacked or even buried materials, as shown in this thesis experimentally for two sample systems. In the first example, the different dielectric functions were obtained by locally changing the carrier concentration in silicon by the implantation of boron. It is shown that the concentration of free charge-carriers can be deduced from the near-field contrast between implanted and pure silicon. For this purpose, two different experimental approaches were used, a non-interferometric one by using variable wavelengths and an interferometric one with a fixed wavelength. As those techniques yield complementary information, they can be used to quantitatively determine the effective carrier concentration. Both approaches yield consistent results for the carrier concentration, which excellently agrees with predictions from literature. While the structures of the first system were in the micrometer regime, the capability to probe buried nanostructures is demonstrated at a sample of indium arsenide quantum dots. Those dots are covered by a thick layer of gallium arsenide. For the first time ever, it is shown experimentally that transitions between electron states in single quantum dots can be investigated by near-field microscopy. By monitoring the near-field response of these quantum dots while scanning the wavelength of the incident light beam, it was possible to obtain characteristic near-field signatures of single dots. Near-field contrasts up to 30 % could be measured for resonant excitation of electrons in the conduction band of the indium arsenide dots. / Die optische Nahfeldmikroskopie hat viel Beachtung auf sich gezogen, da sie die einzige Technologie ist, welche die Untersuchung lokaler optischer Eigenschaften mit Auflösungen unterhalb der Beugungsgrenze ermöglicht. Speziell die streuende Nahfeldmikroskopie erlaubt die zerstörungsfreie Untersuchung von Oberflächen ohne Einschränkung der verwendbaren Wellenlängen. Die Nutzung ist jedoch durch das Vorhandensein entsprechender Lichtquellen beschränkt. Im Rahmen dieser Arbeit wurde diese Beschränkung durch Entwicklung eines streuenden Nahfeldmikroskops überwunden, das einen weit stimmbaren Freie-Elektronen-Laser als primäre Lichtquelle benutzt. Im theoretischen Teil wird gezeigt, dass ein optischer Kontrast erwartet werden kann, wenn Materialien mit unterschiedlichen Dielektrizitätskonstanten kombiniert werden. Es wird hergeleitet, dass diese Unterschiede in unterschiedlichen Streuquerschnitten für das gekoppelte System aus Messkopf und Probe resultieren. Diese Streuquerschnitte definieren die Stärke des Nahfeldsignals, welches auf unterschiedlichen Materialien gemessen werden kann. Ein optischer Kontrast kann also erwartet werden, wenn unterschiedliche Streuquerschnitte untersucht werden. Dass dieses Prinzip auch auf übereinander geschichtete oder sogar verborgene Strukturen angewendet werden kann, wird in dieser Doktorarbeit an zwei Probensystemen experimentell gezeigt. Im ersten Beispiel wurden die unterschiedlichen Dielektrizitätskonstanten durch örtliches Ändern der Ladungsträgerdichte in Silizium durch Bor-Implantation erreicht. Es wird gezeigt, dass die Dichte der freien Ladungsträger an Hand des optischen Kontrastes zwischen implantiertem und reinem Silizium ermittelt werden kann. Zu diesem Zweck wurden zwei unterschiedliche Ansätze verwendet, ein nicht-interferometrischer mittels variabler Wellenlängen und ein interferometrischer mit einer konstanten Wellenlänge. Weil diese Techniken gegensätzliche Informationen liefern, können sie genutzt werden, um die effektive Ladungsträgerdichte quantitativ zu bestimmen. Beide Ansätze lieferten konsistente Resultate für die Trägerdichte, welche sehr gut mit den Vorhersagen der Literatur übereinstimmt. Während die Strukturen im ersten Beispiel im Mikrometer-Bereich lagen, wird die Möglichkeit, verborgene Nanostrukturen zu untersuchen, an Hand einer Probe mit Indiumarsenid Quantenpunkten demonstriert. Diese sind von einer dicken Schicht Galliumarsenid bedeckt. Zum ersten Mal wird experimentell gezeigt, dass Übergänge zwischen Elektronenzuständen in einzelnen Quantenpunkten mit Nahfeldmikroskopie untersucht werden können. Durch die Messung der Nahfeld-Antwort der Quantenpunkte unter Änderung der Wellenlänge des eingestrahlten Lichtes war es möglich, charakteristische Nahfeld-Signaturen der einzelnen Quantenpunkte zu erhalten. Nahfeld-Kontraste bis zu 30 Prozent konnten für die resonante Anregung der Elektronen im Leitungsband der Indiumarsenid Punkte beobachtet werden.

Many genetic processes require enzymes or enzyme complexes that interact simultaneously with distant sites along the genome. Such long-range DNA-enzyme interactions are important for example in gene regulation, DNA replication, repair and recombination. In addition many restriction enzymes depend on interactions between two recognition sites and form therefore a model system for studying long-range communications on DNA. Topic of the present work are Type III restriction enzymes. For these enzymes the communication mechanism between their distant target sites has not been resolved and conflicting models including 3D diffusion, 1D translocation and 1D diffusion have been proposed. Also the role of ATP hydrolysis by their superfamily 2 helicase domains which catalyse functions of many enzyme systems is still poorly understood. To cleave DNA, Type III restriction enzymes sense the relative orientation of their distant target sites and cleave DNA only if at least two of them are situated in an inverted repeat. This process strictly depends on ATP hydrolysis. The aim of this PhD thesis was to elucidate this long-range communication. For this a new single molecule assay was developed using a setup combining magnetic tweezers and objective-type total internal reflection fluorescence microscopy. In addition of being able to mechanically manipulate individual DNA molecules, this assay allows to directly visualize the binding and movement of fluorescently labelled enzymes along DNA. Applying this assay to quantum dot labelled Type III restriction enzymes, a 1D diffusion of the enzymes after binding at their target sites could be demonstrated. Furthermore, it was found that the diffusion depends on the nucleotide that is bound to the ATPase domains of these enzymes. This suggested that ATP hydrolysis acts as a switch to license diffusion from the target site which leads to cleavage. In addition to the direct visualization of the enzyme-DNA interaction, the cleavage site selection, the DNA end influence (open or blocked) and the DNA binding kinetics were measured in bulk solution assays (not part of this thesis). The experimental results were compared to Monte Carlo simulations of a diffusion-collision-model which is proposed as long-range communication in this thesis.

This thesis deals with deterioration observed in cement-concrete cover (CBK) for three selected road sections of highways in the Czech Republic. The main objective was to determine whether concrete failure arose due to alkali-silica reaction, or other mechanism. The deterioration of concrete failure was observed in the macroscopic and microscopic scale. The mostly macroscopically observed deterioration of the concrete were cracks breaking the surface and inner parts of concrete. In micro- scale the microcracks and alcali-silica gels were observed. The CBK deterioration was quantitatively determined by three main parameters: specific length of microcracks on the CBK surface, specific length of microcracks in the drill cores and volume of alcali-silica gels and microcracks in thin sections. According to these indicators it was possible to distinguish two different types of CBK deteriorations. (1) Degradation mainly associated by alkali-silica reaction (observed on highways D11 - Vrbová Lhota and D1) and (2) degradation connected with another mechanism (cycles of freezing and thawing, mechanical degradation) was observed on the highway D5.

Biofilms represent universal strategy for bacterial survival. Living in form of biofilms, bacteria acquire wide range of advantages over planktonically growing cultures. It can be assumed that nearly 99% of world bacterial population is living in form of biofilms. There are benefits and drawbacks associated with bacterial biofilms for mankind. Life in biofilms makes pathogens more effective and persistent through higher antibiotic resistance and helps them to hide before immune system of the host. Mycobacteria, which are capable of forming biofilms on variety of surfaces, differ from most of other bacteria by unique composition of their cell wall. It provides them with high resistance against physical or chemical damage. This is one of the reasons for considering Mycobacterium tuberculosis as a highly potent pathogen. The studies of mycobacterial biofilms are motivated by effort to improve or find new therapeutic methods. This work is aimed at morphological and proteomic comparative analyses of biofilms obtained from Mycobacterium smegmatis grown on surface of glass and silica/zirconium beads, on liquid medium surface or grown submerged in shaken planktonic culture. We have developed technique for preparation of "floating" biofilm sample to be observed in SEM. We have shown that the growth of...

Since the 18th-century scientists are studying diatoms, fascinated by their beauty and diversity. Their nano- and micropatterned biosilica cell walls are outstanding examples of biologically controlled mineral formation. Although the knowledge about diatom cell wall formation increased over the last 60 years, the process is still far away from being completely understood. Diatom cell walls exhibit highly interesting material properties, making them appealing to material scientists. Due to those properties, diatom cell walls are on the brink of becoming powerful tools in nanotechnology. However, the production of tailored silica structures for nanotechnology requires a much better understanding of the processes and components involved in cell wall morphogenesis. Recent studies set the focus on insoluble organic matrices as important parts of this process, suggesting that they act as templates in silica morphogenesis. Therefore, in this study, the occurrence of insoluble organic matrices and their possible silica precipitation activity was analyzed in the three diatom species T. pseudonana, T. oceanica and C. cryptica. For all three species girdle band and valve derived insoluble organic matrices could be identified. The extracted insoluble organic matrices exhibited structural features present in the corresponding biosilica cell walls. The highest similarities were found in the valve derived matrices of C. cryptica. Accessibility studies showed that the biosilica associated insoluble organic matrices of T. pseudonana were only partially accessible, arguing for an entrapment of insoluble organic matrices in the silica, rather than an attachment to the surface of the cell wall. All examined insoluble organic matrices of the three species exhibited intrinsic silica precipitation activity. The most intriguing structures were formed by the insoluble organic matrices of C. cryptica, yielding a porous silica pattern. The addition of biosilica derived soluble components or long-chain polyamines promoted this process and moreover lead to the reconstitution of biosilica-like hierarchical silica pore patterns. The generated silica structures were templated by the underlying structure of the insoluble organic matrix. The result presented in this thesis make this the first study reporting the in vitro generation of diatom biosilica-like hierarchical silica pore patterns using all natural cell wall components. It supports the hypothesis of microplates acting as templates for biosilica morphogenesis and introduces an interesting experimental setup for silica-based in vitro studies on the mechanism of pore formation in diatoms.