Molekulare Genetik (Genetik der Prokaryoten)
Functional analysis of conserved chloroplast and cyanobacterial genes
Cyanobacteria are the ancestors of chloroplasts. Consequently most chloroplast genes show a remarkable degree of sequence similarity to cyanobacterial genes. We are examining the phenotypic consequences of the inactivation of cyanobacterial genes that are homologous to conserved chloroplast genes with unknown function.
This work and analyses of other groups showed that most of the conserved open reading frames in plastids function in photosynthesis. Using this approach we have currently identified five new genes that are essential for efficient photosynthesis in prokaryotic and definitely also in eukaryotic organisms. Several of these conserved ycfs we found to function in the assembly of photosystem I. In a recent approach we were able to elucidate the late steps in photosystem I assembly in cyanobacteria. Two other ycfs are involved in chlorophyll metabolism in cyanobacteria as well as in plants.
Phototaxis in cyanobacteria and the role of photoreceptors
In plants phytochromes are the most important photoreceptors for photomorphogenesis. We were the first who demonstrated the existence of this photoreceptor in the model cyanobacterium Synechocystis sp. PCC 6803. Little is known about the physiological roles played by the red/far red light absorbing photoreceptors in bacteria. For one of the two bona fide phytochromes in the cyanobacterium Synechocystis sp. PCC 6803 we have shown that this protein is involved in the regulation of phototaxis via changes in the c-di-GMP level.
Recently, we have revealed how cyanobacterial cells see the direction of light. The spherical Synechocystis cells focus the light from an unidirectional light source at the opposite site of the cell. This focussed light spot is sensed by the cell which then moves away from the intense light spot but towards the light source. Thus, bacterial cells are physical objects which have micro-optic properties. These properties might have several implications for light harvesting, light damage and light-dependent signalling effects.
Identification and function of regulatory RNA in the phototrophic model organism Synechocystis sp. PCC 6803
Recent data from pro- and eukaryotic organisms show the extremely high potential of non-coding RNAs (ncRNAs) as sequence-specific regulators of gene expression, thereby mediating a plethora of cellular responses to changing environmental clues, and morphological differentiation. Systematic searches for ncRNAs are still lacking for most eubacterial phyla outside the enterobacteria. In general, genes encoding ncRNAs are not annotated during standard genome analysis procedures. Therefore, additional efforts have to be taken to accomplish their identification. In collaboration with the group of Prof. Wolfgang Hess from University of Freiburg we are performing a project on the systematic search for small regulatory RNA molecules in the cyanobacterium Synechocystis sp. PCC 6803 using bioinformatics and molecular methods. Based on this research we verified the existence of a large number of yet unknown functional regulatory RNAs. Our group focuses on investigations of the biological role of small regulatory RNA and the role of the RNA chaperone Hfq in cyanobacteria.
Systems biology of cyanobacterial biofuel production
The project is part of the efforts to efficiently and economically produce so-called biofuels. Our approach is to combine photosynthesis with the synthesis of ethanol in a cyanobacterial cell. Together with our partners, we want to establish a systemic understanding of a photosynthetic prokaryote by experimental analysis of relevant metabolic pathways combined with data-based mathematical modeling. Our model organism is the unicellular cyanobacterium Synechocystis sp. PCC 6803. Well-established genetic tools together with an accumulating body of information from transcriptomic, proteomic and metabolomic data provide an excellent background for systems biology-based modeling, analytical prediction and simulation of cellular processes.
Cyanobacterial circadian clock
The coordination of biological activities into daily cycles provides an important advantage for the fitness of diverse organisms. An internal circadian oscillator drives gene expression in an approximate 24 hours rhythm. The period of this free-running rhythm is highly robust against many changes in the natural environment, for example, in cyanobacteria the clock can compensate for variations in the ambient temperature. But for certain external stimuli (e.g. light, nutrients), the circadian rhythm can be entrained. For the cyanobacterium Synechococcus elongatus, a robust circadian rhythm has been observed under constant darkness conditions and even for complete suppression of the cellular transcription and translation activity. Moreover, only three different cyanobacterial proteins (KaiA, KaiB, and KaiC) are sufficient to achieve a temperature-compensated circadian rhythm of phosphorylation cycles in vitro. KaiC as the major clock component has three intrinsic enzymatic activities: autokinase, autophosphatase and ATPase activities, whereas KaiA enhances the kinase and KaiB the autophosphatase activities, respectively. Thus, in contrast to eukaryotic clock models the cyanobacterial core oscillator operates independently of transcription and translation processes. Most data on the circadian timing process in cyanobacteria have been obtained using the unicellular cyanobacterium Synechococcus elongatus PCC 7942. In different strains of the marine cyanobacteria of the genus Prochlorococcus, components of the oscillator and of the in- and output pathways are missing or truncated. Other model cyanobacteria like Synechocystis sp. PCC 6803 or the filamentous strain Anabaena sp. PCC 7120 harbour multiple gene copies for the three clock components. In this project we analyze non-standard circadian clocks of cyanobacteria.