The case of Chroococcidiopsis: New phylogenetic and morphological insights into ecological important Cyanobacteria

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