Bielefeld University Department of Chemistry Biophysical Chemistry and Photochemistry deutsch

Algae as Model Organisms

Impact in Biotechnology, Medicine and Climate Change

- Photoreceptors such as channel rhodopsins are applied to artificially activate nerve cells by light (optogenetics).
- The mechanism behind one of the most common human genetic diseases, polycystic kidney disease, and many other diseases has been investigated in the model system Chlamydomonas, because the flagella of the alga have much in common with the primary cilium.
-Algal cells produce hydrogen or isoprene upon illumination and are therefore candidates for a direct, environmentally sound conversion of solar energy into fuel or biomass.
- Algae store about half of the globally available carbon dioxide and are therefore a major factor in the investigation of the climate change.

The Green Alga Chlamydomonas

Chlamydomonas reinhardtii is a unicellular green alga with a size of about 10 micrometers and is found all over the world. It serves as a simple model organism for the investigation of photosynthesis and processing of light signals.

With the help of two flagella it reacts to the light conditions of the environment (phototaxis). It uses a biological clock for daily time keeping, which is synchronized by light (circadian rhythm). To investigate the entrainment of this rhythm Chlamydomonas has already been sent to space on the Space Shuttle.

The Diatom Phaeodactylum

Diatoms are unicellular, photosynthetic organisms, which are found in marine and freshwater environments, for example as part of the plankton. Phaeodactylum tricornutum is one of the best characterized diatoms. Its genome has been fully sequenced.

Diatoms contribute significantly (around one fifth) to primary productivity on Earth. Consequently, one in five oxygen molecules consumed by us has been produced by a diatom.

Photoreceptors (FOR1261)

Within the framework of the interdisciplinary Research Group 1261, we are investigating the role and the mechanism of photoreceptors in unicellular model algae.

Typical for a member of the plant family, Chlamydomonas contains phototropin und cryptochromes. However, it is lacking the whole family of the red light-sensitive phytochromes. Instead, the alga contains an animal-like cryptochrome (aCRY), which is the only flavoprotein so far that is activated by red light (see Plant Cell 2012).

Additionally, rhodopsins are found in the green alga such as the channelrhodopsins, which are responsible for phototaxis. Phototropin protects photosynthesis from harmful light intensities (siehe Nature 2016). aCRY regulates the reproduction and plant cryptochrome the circadian rhythm (siehe Plant Physiol. 2017a 2017b).

The green alga thereby offers the opportunity to study the mechanism of almost all common photoreceptors within a comparatively simple organism.

For our biophysical investigations, we overproduce the photoreceptors or segments thereof in larger amounts in E. coli (such as the cryptochrome, see J. Biol. Chem. 2007). From similarities or differences in the properties of the Chlamydomonas photoreceptors as compared to those of higher plants, one can draw conclusions on the relevant processes and observe evolutionary developments.

Phaeodactylum contains different photoreceptors than plants, because it is a secondary endosymbiont. Cryptochromes and phytochromes are still found in the diatom. However, phototropin is not produced. Instead, aureochrome regulates some of the blue light responses such as the acclimation to high light.

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