Arctic, Antarctic and alpine biological soil crusts (BSCs) are formed by adhesion of soil particles to exopolysaccharides (EPSs) excreted by cyanobacterial and green algal communities, the pioneers and main primary producers in these habitats. These BSCs provide and influence many ecosystem services such as soil erodibility, soil formation and nitrogen (N) and carbon (C) cycles. In cold environments degradation rates are low and BSCs continuously increase soil organic C; therefore, these soils are considered to be CO2 sinks. This work provides a novel, nondestructive and highly comparable method to investigate intact BSCs with a focus on cyanobacteria and green algae and their contribution to soil organic C. A new terminology arose,basedonconfocallaserscanningmicroscopy(CLSM) 2-D biomaps, dividing BSCs into a photosynthetic active layer (PAL) made of active photoautotrophic organisms and a photosynthetic inactive layer (PIL) harbouring remnants of cyanobacteria and green algae glued together by their remaining EPSs. By the application of CLSM image analysis (CLSM–IA) to 3-D biomaps, C coming from photosynthetic activeorganismscouldbevisualizedasdepthprofileswithC peaks at 0.5 to 2mm depth. Additionally, the CO2 sink character of these cold soil habitats dominated by BSCs could be highlighted, demonstrating that the first cubic centimetre of soil consists of between 7 and 17% total organic carbon, identified by loss on ignition.

Like many other bacteria, the opportunistic pathogen P. aeruginosa encodes a broad network of enzymes that regulate the intracellular concentration of the second messenger c-di-GMP. One of these enzymes is the phosphodiesterase NbdA that consists of three domains: a membrane anchored, putative sensory MHYT domain, a non-functional diguanylate cyclase domain with degenerated GGDEF motif and an active PDE domain with EAL motif. Analysis of the nbdA open reading frame by 5’-RACE PCR revealed an erroneous annotation of nbdA in the Pseudomonas database with the ORF 170 bp shorter than previously predicted. The newly defined promoter region of nbdA contains recognition sites for the alternative sigma-factor RpoS as well as the transcription factor AmrZ. Promoter analysis within PAO1 wt as well as rpoS and amrZ mutant strains utilizing transcriptional fusions of the nbdA promoter to the reporter gene lacZ revealed transcriptional activation of nbdA by RpoS in stationary growth phase and transcriptional repression by AmrZ. Additionally, no influence of nitrite and neither exogenous nor endogenous NO on nbdA transcription could be shown in this study. However, deletion of the nitrite reductase gene nirS led to a strong increase of nbdA promoter activity which needs to be characterized further. Predicted secondary structures of the 5’-UTR of the nbdA mRNA indicated either an RNA thermometer function of the mRNA or post-transcriptional regulation of nbdA by the RNA binding proteins RsmA and RsmF. Nevertheless, translational studies using fusions of the 5’ UTR of nbdA to the reporter gene bgaB did not verify either of these hypotheses. In general, nbdA translational levels were very low and neither the production of the reporter BgaB nor genomically encoded NbdA could be detected on a western blot. Overproduction of NbdA variants induced many phenotypic changes in motility and biofilm formation. But strains overproducing variants containing the MHYT domain revealed greatly elongated cells and were impaired in surface growth, indicating a misbalance in the membrane protein homeostasis. Therefore, these phenotypes have to be interpreted very critically. Microscopic studies with fluorescently tagged NbdA revealed either a diffuse fluorescent signal of NbdA or the formation of fluorescent foci which were located mainly at the cell poles. Co-localization studies with the polar flagellum and the chemotaxis protein CheA showed that NbdA is not generally localizing to the flagellated cell pole. NbdA localization indicates the control of a specific local c-di-GMP pool in the cell which is most likely involved in MapZ mediated chemotactic flagellar motor switching.

Compared to our current knowledge of neuronal excitation, little is known about the development and maturation of inhibitory circuits. Recent studies show that inhibitory circuits develop and mature in a similar way like excitatory circuit. One such similarity is the development through excitation, irrespective of its inhibitory nature. Here in this current study, I used the inhibitory projection between the medial nucleus of the trapezoid body (MNTB) and the lateral superior olive (LSO) as a model system to unravel some aspects of the development of inhibitory synapses. In LSO neurons of the rat auditory brainstem, glycine receptor-mediated responses change from depolarizing to hyperpolarizing during the first two postnatal weeks (Kandler and Friauf 1995, J. Neurosci. 15:6890-6904). The depolarizing effect of glycine is due to a high intracellular chloride concentration ([Cl-]i), which induces a reversal potential of glycine (EGly) more positive than the resting membrane potential (Vrest). In older LSO neurons, the hyperpolarizing effect is due to a low [Cl-]i (Ehrlich et al., 1999, J. Physiol. 520:121-137). Aim of the present study was to elucidate the molecular mechanism behind Clhomeostasis in LSO neurons which determines polarity of glycine response. To do so, the role and developmental expression of Cl-cotransporters, such as NKCC1 and KCC2 were investigated. Molecular biological and gramicidin perforated patchclamp experiments revealed, the role of KCC2 as an outward Cl-cotransporter in mature LSO neurons (Balakrishnan et al., 2003, J Neurosci. 23:4134-4145). But, NKCC1 does not appear to be involved in accumulating chloride in immature LSO neurons. Further experiments, indicated the role of GABA and glycine transporters (GAT1 and GLYT2) in accumulating Cl- in immature LSO neurons. Finally, the experiments with hypothyroid animals suggest the possible role of thyroid hormone in the maturation of inhibitory synapse. Altogether, this thesis addressed the molecular mechanism underlying the Cl- regulation in LSO neurons and deciphered it to some extent.

Proteins of the intermembrane space of mitochondria are generally encoded by nuclear genes that are synthesized in the cytosol. A group of small intermembrane space proteins lack classical mitochondrial targeting sequences, but these proteins are imported in an oxidation-driven reaction that relies on the activity of two components, Mia40 and Erv1. Both proteins constitute the mitochondrial disulfide relay system. Mia40 functions as an import receptor that interacts with incoming polypeptides via transient, intermolecular disulfide bonds. Erv1 is an FAD-binding sulfhydryl oxidase that activates Mia40 by re-oxidation, but the process how Erv1 itself is re-oxidized has been poorly understood. Here, I show that Erv1 interacts with cytochrome c which provides a functional link between the mitochondrial disulfide relay system and the respiratory chain. This mechanism not only increases the efficiency of mitochondrial inport by the re-oxidation of Erv1 and Mia40 but also prevents the formation of deleterious hydrogen peroxide within the intermembrane space. Thus, the miochondrial disulfide relay system is, analogous to that of the bacterial periplasm, connected to the electron transport chain of the inner membrane, which possibly allows an oxygen-dependend regulation of mitochondrial import rates. In addition, I modeled the structure of Erv1 on the basis of the Saccharomyces cerevisiae Erv2 crystal structure in order to gain insight into the molecular mechanism of Erv1. According to the high degree of sequence homologies, various characteristics found for Erv2 are also valid for Erv1. Finally, I propose a regulatory function of the disulfide relay system on the respiratory chain. The disulfide relay system senses the molecular oxygen levels in mitochondria and, thus, is able to adapt respiratory chain activity in order to prevent wastage of NADH and production of ROS.

Cyanobacteria are the only prokaryotes with the ability to conduct oxygenic photosynthesis, therefore having major influence on the evolution of life on earth. Their diverse morphology was traditionally the basis for taxonomy and classification. For example, the genus Chroococcidiopsis has been classified within the order Pleurocapsales, based on a unique reproduction modus by baeocytes. Recent phylogenetic results suggested a closer relationship of this genus to the order Nostocales. However, these studies were based mostly on the highly conserved 16S rRNA and a small selection of Chroococcidiopsis strains. One aim of this present thesis was to investigate the evolutionary relationships of the genus Chroococcidiopsis, the Pleurocapsales and remaining cyanobacteria using 16S rRNA, rpoC1 and gyrB gene. Including the single gene, as the multigene analyses of 97 strains clearly showed a separation of the genus Chroococcidiopsis from the Pleurocapsales. Furthermore, a sister relationship between the genus Chroococcidiopsis and the order Nostocales was confirmed. Consequently, the monogeneric family Chroococcidiopsidaceae Geitler ex. Büdel, Donner & Kauff familia nova is justified. The phylogenetic analyses also revealed the polyphyly of the remaining Pleurocapsales, due to the fact that the strain Pleurocapsa PCC 7327 was always separated from other strains. This is supported by differences in their metabolism, ecology and physiology. A second aim of this study was to investigate the thylakoid arrangement of Chroococcidiopsis and a selection of cyanobacterial strains. The investigation of 13 strains with Low Temperature Scanning Electron Microscopy revealed two unknown thylakoidal arrangements within Chroococcidiopsis (parietal and stacked). This result revised the knowledge of the thylakoid arrangement in this genus. Previously, only a coiled arrangement was known for three strains. Based on the data of 66 strains, the feature thylakoid arrangement was tested as a potential feature for morphological identification of cyanobacteria. The results showed a strong relationship between the group assignment of cyanobacteria and their thylakoid arrangements. Hence, it is in general possible to conclude from this certain phenotypic character the affiliation to a particular family, order or genus. The third aim of this study was to investigate biogeographical patterns of the worldwide distributed genus Chroococcidiopsis. The phylogenetic analysis suggested that the genus do not have biogeographical patterns, which is in contrast with a recent study on hypolithic living Chroococcidiopsis strains and the majority of phylogeographic analysis of microorganisms. Further analysis showed no separation of different life-strategies within the genus. These results could be related to the genetic markers utilized, which may not contain biogeographical information. Hence the present study can neither exclude nor prove the possibility of biogeographic and life-strategy patterns in the genus Chroococcidiopsis. Future research should be focused on finding appropriate genetic markers investigate of evolutionary relationships and biogeographical patterns within Chroococcidiopsis.