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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.
Carbon fibre reinforced epoxies (CFRE) are a class of high performance, light-weight composites
that show outstanding, weight-specific (thermo-)mechanical properties. A glassy and
highly cross-linked epoxy matrix provides the composite with a high thermal resistance, but
makes the CFRE also inherently brittle and susceptible to cracks and impacts. One strategy
to overcome this drawback and to improve fracture toughness of epoxy matrices is to modify
the underlying morphology with additional substructures (domains in the nano and/or micron
size range). This allows increasing the energy that is required to initiate or propagate a crack
within the material. The present work contributes to a better understanding of the effect
of substructure-forming, self-assembling block copolymers (BCP) and pre-formed core-shell
rubber particles (CSR) on the toughness and impact behaviour of thin CFREs and their epoxy
matrices. Using a new thermo-optical measurement technique, it is shown that the phaseseparation
process of BCP-rich domains is solely driven by the degree of cure of the epoxy
matrix. Also, it is found that the process of BCP phase-separation, e.g. the BCP-rich domain
size, changes strongly in the presence of carbon fibres. Low concentrations of BCPs (7wt.-%)
yield a 2.5-fold enhancement of the resistance to interlaminar fracture of the CFRE (Mode),
already. Using CSR particles, on the other hand, the energy required to initiate delamination
(Mode II) within the CFRE increases by 160 %. Subsequently, by a hybridization of BCP
and CSR modifiers, after low energy impacts, when both load cases occur in combination, a
synergistic damage volume reduction by more than 67% is achieved. Hence, the generated
material systems and the acquired understanding allow future CFRE based structures to be
even thinner than current design solutions, without affecting their structural integrity under
impact loads.