Photochemisch strukturierte computergenerierte Hologramme in Bakteriorhodopsin-Schichten

Ziel dieser Dissertation ist die Untersuchung des photochemischen Aufzeichungsprozesses von computergenerierte Hologrammen (CGH's) innerhalb des Biomaterials Bakteriorhodopsin (BR). Dabei werden folgende Schwerpunkte detailliert analysiert: - Implementierung und Untersuchung verschiedene Algorithmen zur Berechnung von CGH's. Die Algorithmen sind insbesondere hinsichtlich der Verwendung des Biomaterials BR als Hologrammedien zu beurteilen. - Untersuchung des Aufzeichungsprozesses von CGH's mittels eines direkten Laserschreibsystems. Bei den CGH-Herstellungsverfahren werden die physikalischen und biochemischen Eigenschaften von BR gezielt ausgenutzt, um die für die CGH-Aufzeichnung optimale Oberflächenprofilierung und/oder Brechungsindexmodulation zu erreichen

Energy-filtered transmission electron microscopy of biological samples on highly transparent carbon nanomembranes

Ultrathin carbon nanomembranes (CNM) comprising crosslinked biphenyl precursors have been tested as support films for energy-filtered transmission electron microscopy (EFTEM) of biological specimens. Due to their high transparency CNM are ideal substrates for electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) of stained and unstained biological samples. Virtually background-free elemental maps of tobacco mosaic virus (TMV) and ferritin have been obtained from samples supported by ~ 1 nm thin CNM. Furthermore, we have tested conductive carbon nanomembranes (cCNM) comprising nanocrystalline graphene, obtained by thermal treatment of CNM, as supports for cryoEM of ice-embedded biological samples. We imaged ice-embedded TMV on cCNM and compared the results with images of ice-embedded TMV on conventional carbon film (CC), thus analyzing the gain in contrast for TMV on cCNM in a quantitative manner. In addition we have developed a method for the preparation of vitrified specimens, suspended over the holes of a conventional holey carbon film, while backed by ultrathin cCNM

Recent advances in exploring physiology and biodiversity of ectomycorrhizas highlight the functioning of these symbioses in ecosystems

Ectomycorrhizas, the dominating mycorrhizal symbiosis in boreal, temperate and some tropical forests, are formed by 5000-6000 species of the asco- and basidiomycetes. This high diversity of fungal partners allows optimal foraging and mobilisation of various nitrogen and phosphorus forms from organic soil layers. In this review, two approaches to study the functioning of this multitude of symbiotic associations are presented. On selected culture models, physiological and molecular investigations have shown that the supply of hexoses has a key function in controlling the plant^fungus interaction via partner-specific regulation of gene expression. Environmental factors which affect fungal carbon supply, such as increased nitrogen availability, also affect mycorrhiza formation. Based on such laboratory results, the adaptative capability of ectomycorrhizas to changing field conditions is discussed. The second approach consists of analysing the distribution of mycorrhizas in ecosystem compartments and to relate distribution patterns to variations of ecological factors. Recent advances in identification of fungal partners in ectomycorrhizas by analysing the internal transcribed spacer of ribosomal DNA are presented, which can help to resolve sampling problems in field studies. The limits of the laboratory and the field approaches are discussed. Despite some problems, this combined approach is the most promising. Direct investigation of gene expression, which has been introduced for soil bacteria, will be difficult in the case of mycorrhizal fungi which constitute organisms with functionally varying structure

Schutz von Holz- und TMP-Holzstoff-Oberflächen vor lichtinduzierter Vergilbung durch chemische Modifikation des Lignins

Ein neuer Reaktionsmechanismus der Chromophorenbildung im Lignin wurde bei der lichtinduzierten Vergilbung von Holz- und TMP-Holzstoff-Oberflächen identifiziert. Die Photolabilität der acetylierten Oberflächen wurde anhand von Untersuchungen mit Ligninmodellsubstanzen nachgewiesen. Basierend auf dieser Erkenntnis wurde eine neuartige Schutzmethode für Holz- und TMP-Holzstoff-Oberflächen vor lichtinduzierter Vergilbung entwickelt

Growth inhibition of an Araucaria angustifolia (Coniferopsida) fungal seed pathogen, Neofusicoccum parvum, by soil streptomycetes

Background: Araucariaceae are important forest trees of the southern hemisphere. Life expectancy of their seedlings can largely be reduced by fungal infections. In this study we have isolated and characterized such a fungus and investigated the potentia

The clock genes Period 2 and Cryptochrome 2 differentially balance bone formation

Background: Clock genes and their protein products regulate circadian rhythms in mammals but have also been implicated in various physiological processes, including bone formation. Osteoblasts build new mineralized bone whereas osteoclasts degrade it thereby balancing bone formation. To evaluate the contribution of clock components in this process, we investigated mice mutant in clock genes for a bone volume phenotype. Methodology/Principal Findings: We found that Per2Brdm1 mutant mice as well as mice lacking Cry2-/- displayed significantly increased bone volume at 12 weeks of age, when bone turnover is high. Per2Brdm1 mutant mice showed alterations in parameters specific for osteoblasts whereas mice lacking Cry2-/- displayed changes in osteoclast specific parameters. Interestingly, inactivation of both Per2 and Cry2 genes leads to normal bone volume as observed in wild type animals. Importantly, osteoclast parameters affected due to the lack of Cry2, remained at the level seen in the Cry2-/- mutants despite the simultaneous inactivation of Per2. Conclusions/Significance: This indicates that Cry2 and Per2 affect distinct pathways in the regulation of bone volume with Cry2 influencing mostly the osteoclastic cellular component of bone and Per2 acting on osteoblast parameters

Systems analysis of bioenergetics and growth of the extreme halophile Halobacterium salinarum

Halobacterium salinarum is a bioenergetically flexible, halophilic microorganism that can generate energy by respiration, photosynthesis, and the fermentation of arginine. In a previous study, using a genome-scale metabolic model, we have shown that the archaeon unexpectedly degrades essential amino acids under aerobic conditions, a behavior that can lead to the termination of growth earlier than necessary. Here, we further integratively investigate energy generation, nutrient utilization, and biomass production using an extended methodology that accounts for dynamically changing transport patterns, including those that arise from interactions among the supplied metabolites. Moreover, we widen the scope of our analysis to include phototrophic conditions to explore the interplay between different bioenergetic modes. Surprisingly, we found that cells also degrade essential amino acids even during phototropy, when energy should already be abundant. We also found that under both conditions considerable amounts of nutrients that were taken up were neither incorporated into the biomass nor used as respiratory substrates, implying the considerable production and accumulation of several metabolites in the medium. Some of these are likely the products of forms of overflow metabolism. In addition, our results also show that arginine fermentation, contrary to what is typically assumed, occurs simultaneously with respiration and photosynthesis and can contribute energy in levels that are comparable to the primary bioenergetic modes, if not more. These findings portray a picture that the organism takes an approach toward growth that favors the here and now, even at the cost of longer-term concerns. We believe that the seemingly "greedy" behavior exhibited actually consists of adaptations by the organism to its natural environments, where nutrients are not only irregularly available but may altogether be absent for extended periods that may span several years. Such a setting probably predisposed the cells to grow as much as possible when the conditions become favorable

Two-Photon-Absorption Triggered Release of 5-Fluorouracil from Isomer-Pure Polymer Bound Syn-Head-to-Head Dimers for Novel Intraocular Lenses

Different stereoisomers of the cytotoxic 5-fluorouracil (5FU) homodimers were synthesized by photochemical [2+2]-cycloaddition and polymerized into MMA/HEMA to form a novel drug-loaded copolymer for intraocular lenses as irradiation-activated treatment for secondary cataract. Three isomers were obtained, and showed significant differences in cleavage efficiency on photo-cleavage via single-photon-absorption (SPA) and two-photon-absorption (TPA). The most efficient TPA cleavage rate was observed for the syn-head-to-head 5FU dimer, which was, consequently, used for drug loading of the polymeric material to obtain a drug-loaded material of higher efficiency compared to previous works. The light and thermal stability of the polymer were confirmed and multi-dose release of the drug in aqueous solution for possible repeated treatment of cataract was proven