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.

Cell division and cell elongation are fundamental processes for growth. In contrast to animal cells, plant cells are surrounded by rigid walls and therefore loosening of the wall is required during elongation. On the other hand, vacuole size has been shown to correlate with cell size and inhibition of vacuolar expansion limits cell growth. However, the specific role of the vacuole during cell elongation is still not fully resolved. Especially the question whether the vacuole is the leading unit during cellular growth or just passively expands upon water uptake remains to be answered. Here, we review recent findings about the contribution of the vacuole to cell elongation. In addition, we also discuss the connection between cell wall status and vacuolar morphology. In particular, we focus on the question whether vacuolar size is dictated by cell size or vice versa and share our personnel view about the sequential steps during cell elongation.

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.

Cyanobacteria of biological soil crusts (BSCs) represent an important part of circumpolar and Alpine ecosystems, serve as indicators for ecological condition and climate change, and function as ecosystem engineers by soil stabilization or carbon and nitrogen input. The characterization of cyanobacteria from both polar regions remains extremely important to understand geographic distribution patterns and community compositions. This study is the first of its kind revealing the efficiency of combining denaturing gradient gel electrophoresis (DGGE), light microscopy and culture-based 16S rRNA gene sequencing, applied to polar and Alpine cyanobacteria dominated BSCs. This study aimed to show the living proportion of cyanobacteria as an extension to previously published meta-transcriptome data of the same study sites. Molecular fingerprints showed a distinct clustering of cyanobacterial communities with a close relationship between Arctic and Alpine populations, which differed from those found in Antarctica. Species richness and diversity supported these results, which were also confirmed by microscopic investigations of living cyanobacteria from the BSCs. Isolate-based sequencing corroborated these trends as cold biome clades were assigned, which included a potentially new Arctic clade of Oculatella. Thus, our results contribute to the debate regarding biogeography of cyanobacteria of cold biomes.