Forschungsschwerpunkte der AG Caspari
The lab is interested in researching biogenesis and maintenance of photosynthesis using the model green alga Chlamydomonas reinhardtii. We seek to understand both how the photosynthetic machinery is set up, starting from protein import into the chloroplast, and how degradation of this machinery can be prevented in aging cultures, including through the use of symbiotic nutrient recycling. The aim is to achieve greater control over gain and loss of the photosynthetic machinery to enable biotechnological exploitation of stable photosynthesizing cultures capable of continuously generating a desired product.
Protein import
The biogenesis of the photosynthetic machinery is based on a complicated interplay of protein import and expression of the chloroplast genome. Highly sequence-divergent N-terminal chloroplast transit peptides (cTPs) determine the import of cytosolically produced proteins. Research in the lab builds on the finding that cTPs consist of unstructured sequence elements upstream and downstream of a central amphipathic helix (Caspari et al. 2023) and that these sequence elements extend beyond the site where cTPs are cleaved from the transported protein (Caspari 2022). We use a genetic screen to test the role of cTP elements in protein targeting. To do this, we use leaky stop codon technology (Caspari 2020), which allows a combination of complementation and fluorescence microscopy. Similarly, we are interested in finding out whether the affinity of the transit peptides for the lipid composition of the target organelle membranes plays a role in determining the subcellular target site.
Escaping decline
Chlamydomonas cultures follow the same growth pattern as other microorganisms in the lab: an exponential phase is followed by a stationary phase, and then a phase of decline. That photosynthetic microbes should die off is puzzling, since they do not suffer an energy limitation. If cells merely stopped dividing, stationary phase culture could be an ideal platform for biotechnological exploitation since a larger proportion of the energy turnover could be channelled into a desired product. We are therefore interested in studying the causes of culture decline, and the accompanying photosynthetic downregulation. We are also interested in developing experimental evolution protocols for Chlamydomonas, e.g. by using sexual reproduction mutagenic agents, to try and push algal cultures to maintain high photosynthetic rates.
With a little help from my friends
In natural ecosystems, waste is recycled through the interaction of a variety of organisms, preventing the die-off observed in axenic cultures. The goal is therefore to establish microbial mini-ecosystems capable of keeping Chlamydomonas cultures alive in the long term, starting from random environmental biota, e.g. soil samples (Chlamydomonas is a soil-dwelling alga). We also aim to develop closer forms of symbiotic dependencies by relying on protein import. This idea builds on work on the evolution of protein import by mitochondria and chloroplasts from a bacterial defence system against antimicrobial peptides (Garrido und Caspari et al. 2020, Caspari und Lafontaine 2021, Caspari et al. 2023), suggesting that it may be possible to engineer bacteria to import proteins. Ultimately, the goal is to combine a protein-exporting algal strain with a protein-importing bacterium to artificially induce symbiosis.
Publications
Here you can find a list of our previously published papers.
Team
Here you can find a list of the current members of the research group.