Novel insights into biosynthesis and uptake of rhamnolipids and their precursors

The human pathogenic bacterium Pseudomonasaeruginosa produces rhamnolipids, glycolipids with functionsfor bacterial motility, biofilm formation, and uptake of hydrophobicsubstrates. Rhamnolipids represent a chemically heterogeneousgroup of secondary metabolites composed of one ortwo rhamnose molecules linked to one or mostly two 3-hydroxyfatty acids of various chain lengths. The biosyntheticpathway involves rhamnosyltransferase I encoded by the rhlABoperon, which synthesizes 3-(3-hydroxyalkanoyloxy)alkanoicacids (HAAs) followed by their coupling to one rhamnose moiety.The resulting mono-rhamnolipids are converted to dirhamnolipidsin a third reaction catalyzed by therhamnosyltransferase II RhlC. However, the mechanism behindthe biosynthesis of rhamnolipids containing only a singlefatty acid is still unknown. To understand the role of proteinsinvolved in rhamnolipid biosynthesis the heterologous expressionof rhl-genes in non-pathogenic Pseudomonas putidaKT2440 strains was used in this study to circumvent the complexquorum sensing regulation in P. aeruginosa. Our resultsreveal that RhlA and RhlB are independently involved inrhamnolipid biosynthesis and not in the form of a RhlAB heterodimercomplex as it has been previously postulated.Furthermore, we demonstrate that mono-rhamnolipids providedextracellularly as well as HAAs as their precursors are generallytaken up into the cell and are subsequently converted todi-rhamnolipids by P. putida and the native host P. aeruginosa.Finally, our results throw light on the biosynthesis ofrhamnolipids containing one fatty acid,which occurs by hydrolyzationof typical rhamnolipids containing two fatty acids,valuable for the production of designer rhamnolipids with desiredphysicochemical properties

Tumor-Associated Disialylated Glycosphingolipid Antigen-Revealing Antibodies Found in Melanoma Patients' Immunoglobulin Repertoire Suggest a Two-Direction Regulation Mechanism Between Immune B Cells and the Tumor

There is far less information available about the tumor infiltrating B (TIL-B) cells, than about the tumor infiltrating T cells. We focused on discovering the features and potential role of B lymphocytes in solid tumors. Our project aimed to develop innovative strategies to define cancer membrane structures. We chose two solid tumor types, with variable to considerable B cell infiltration. The strategy we set up with invasive breast carcinoma, showing medullary features, has been introduced and standardized in metastatic melanoma. After detecting B lymphocytes by immunohistochemistry, VH-JH, Vκ-Jκ immunoglobulin rearranged V region genes were amplified by RT-PCR, from TIL-B cDNA. Immunoglobulin variable-region genes of interest were cloned, sequenced, and subjected to a comparative DNA analysis. Single-chain variable (scFv) antibody construction was performed in selected cases to generate a scFv library and to test tumor binding capacity. DNA sequence analysis revealed an overrepresented VH3-1 cluster, represented both in the breast cancer and the melanoma TIL-B immunoglobulin repertoire. We observed that our previously defined anti GD3 ganglioside-binder antibody-variable region genes were present in melanoma as well. Our antibody fragments showed binding potential to disialylated glycosphingolipids (GD3 ganglioside) and their O acetylated forms on melanoma cancer cells. We conclude that our results have a considerable tumor immunological impact, as they reveal the power of TIL-B cells to recognize strong tumor-associated glycosphingolipid structures on melanomas and other solid tumors. As tumor-derived gangliosides affect immune cell functions and reduce the B lymphocytes' antibody production, we suspect an important B lymphocyte and cancer cell crosstalk mechanism. We not only described the isolation and specificity testing of the tumor infiltrating B cells, but also showed the TIL-B cells' highly tumor-associated GD3 ganglioside-revealing potential in melanomas. The present data help to identify new cancer-associated biomarkers that may serve for novel cancer diagnostics. The two-direction regulation mechanism between immune B cells and the tumor could eventually be developed into an innovative cancer treatment strategy

Mitochondrial-Nuclear DNA Interactions Contribute to the Regulation of Nuclear Transcript Levels as Part of the Inter-Organelle Communication System

Nuclear and mitochondrial organelles must maintain a communication system. Loci on the mitochondrial genome were recently reported to interact with nuclear loci. To determine whether this is part of a DNA based communication system we used genome conformation capture to map the global network of DNA-DNA interactions between the mitochondrial and nuclear genomes (Mito-nDNA) in Saccharomyces cerevisiae cells grown under three different metabolic conditions. The interactions that form between mitochondrial and nuclear loci are dependent on the metabolic state of the yeast. Moreover, the frequency of specific mitochondrial - nuclear interactions (i.e. COX1-MSY1 and Q0182-RSM7) showed significant reductions in the absence of mitochondrial encoded reverse transcriptase machinery. Furthermore, these reductions correlated with increases in the transcript levels of the nuclear loci (MSY1 and RSM7). We propose that these interactions represent an inter-organelle DNA mediated communication system and that reverse transcription of mitochondrial RNA plays a role in this process

Towards a Generalized Framework for theAnalysis of Solar Cell Performance basedon the Principle of Detailed Balance

The principle of detailed balance forms the basis of the present thesis. It states that all microscopic processes in thermodynamic equilibrium are equal to their respective counter processes. For solar cells in thermodynamic equilibrium, for example, as many photons get absorbed by the cell as are emitted. Shockley and Queisser used this principle to determine a theoretical conversion efficiency limit for a solar cell with a given band gap energy, using additionally the assumption that all photons with energies higher than the band gap energy are absorbed and that there is zero absorption below the band gap energy. This so-called step-function in absorption is one of the idealizations of the model as no material shows this kind of sharp absorption edge. There are different conventions on how to quantify the band gap energy, each of which is preferentially used in different solar cell technology communities. This band gap energy, for instance, is used to quantify losses that occur in the solar cell with respect to the ideal solar cell after Shockley and Queisser. [...

Towards a generalized framework for the analysis of solar cell performance based on the principle of detailed balance

The principle of detailed balance forms the basis of the present thesis. It states that all microscopic processes in thermodynamic equilibrium are equal to their respective counter processes. For solar cells in thermodynamic equilibrium, for example, as many photons get absorbed by the cell as are emitted. Shockley and Queisser used this principle to determine a theoretical conversion efficiency limit for a solar cell with a given band gap energy, using additionally the assumption that all photons with energies higher than the band gap energy are absorbed and that there is zero absorption below the band gap energy. This so-called step-function in absorption is one of the idealizations of the model as no material shows this kind of sharp absorption edge. There are different conventions on how to quantify the band gap energy, each of which is preferentially used in different solar cell technology communities. This band gap energy, for instance, is used to quantify losses that occur in the solar cell with respect to the ideal solar cell after Shockley and Queisser. This thesis introduces a procedure based on the theory of Shockley and Queisser to determine the band gap energy that is applicable to all technologies. It is derived from a mathematical definition of a distribution of band gap energies that is calculated solely from the external quantum efficiency of the solar cell. This so-called Shockley-Queisser band gap energy is then used to quantify voltage loss mechanisms with respect to the ideal case. Because the Shockley-Queisser band gap energy is not determined from internal material properties, it allows for the comparison of these loss mechanisms consistently throughout all solar cell technologies.In contrast, to determine the efficiency potential of theoretical materials generated via first-principle calculations it is necessary to deduce external solar cell parameters such as the short-circuit current from internal material properties such as the complex refractive index. The state-of-the-art model by Yu and Zunger used to determine efficiency limits from computationally or experimentally derived absorption spectra, however, is not compatible with the principle of detailed balance. In the present thesis it is shown that the refractive index must be taken into account in order to achieve compatibility with the principle of detailed balance. A consistent model is described and a selection metric for computational high-throughput materials screening is developed. This selection metric is then applied to a variety of materials. The efficiency potential is shown to differ from the state-of-the-art model by up to \SI{20}{\percent}.After looking at the solar cell solely from the outside and establishing a model that connects internal and external parameters, the final topic in the thesis is dedicated to modelling the organic solar cell exclusively by internal means. Due to the low dielectric constants typical of organic materials, the generated electron-hole pairs are found as strongly bound excitons. To efficiently split these excitons an additional state is needed, namely the charge transfer state. Based on the principle of detailed balance a 0-dimensional rate model is described that accounts for this extra electronic state. It is shown that for this model both the superposition of electro and photoluminescence and the opto-electronic reciprocity theorem by Rau hold under non-saturation conditions. The occupation of the charge transfer state as well as the collection efficiency are thoroughly discussed for the transfer rate models according to both the Miller-Abrahams and Marcus theory

Selection Metric for Photovoltaic Materials Screening Based on Detailed-Balance Analysis

The success of recently discovered absorber materials for photovoltaic applications has been generating increasing interest in systematic materials screening over the last years. However, the key for a successful materials screening is a suitable selection metric that goes beyond the Shockley-Queisser theory that determines the thermodynamic efficiency limit of an absorber material solely by its band-gap energy. In this work, we develop a selection metric to quantify the potential photovoltaic efficiency of a material. Our approach is compatible with detailed balance and applicable in computational and experimental materials screening. We use the complex refractive index to calculate radiative and nonradiative efficiency limits and the respective optimal thickness in the high mobility limit. We compare our model to the widely applied selection metric by Yu and Zunger [Phys. Rev. Lett. 108, 068701 (2012)] with respect to their dependence on thickness, internal luminescence quantum efficiency, and refractive index. Finally, the model is applied to complex refractive indices calculated via electronic structure theory

Efficiency Potential of Photovoltaic Materials and Devices Unveiled by Detailed-Balance Analysis

A consistent mathematical approach is presented that connects the Shockley-Queisser (SQ) theory to the analysis of real-world devices. We demonstrate that the external photovoltaic quantum efficiency QPVe of a solar cell results from a distribution of SQ-type band-gap energies and how this distribution is derived from experimental data. This leads us to the definition of a photovoltaic band-gap energy EPVg as a reference value for the analysis of the device performance. For a variety of solar-cell devices, we show that the combination of QPVe and electroluminescence measurements allows for a detailed loss analysis that is fully compatible with the principle of detailed balance

Degradation of tandem solar cells: Separating matching effects from Staebler-Wronski Effect using the Power-Matching-Method

In thin-film tandem solar cells the sub cells are usually connected in series. The inherent current-limitation needs to be considered when optimizing the efficiency, but furthermore leads to challenges when comparing the sub cells performances of differently matched tandem cells. We have introduced the Power-Matching-Method that characterizes the device not only under one standard spectrum but under various spectral distributions. By this method, the same tandem cell can be characterized under various matching conditions. Based on simulations, we demonstrate a convenient way to compare differently matched tandem solar cells. Moreover, our simulations show that the method allows distinguishing between matching effects and changes in the sub-cells properties, e.g. changes due to the Staebler-Wronski-Effect