Blue algae defy light stress

Researchers are investigating the flexibility of cyanobacteria under changing environmental conditions

Electron micrograph of the cyanobacterium Synechocystis PCC 6803 (cell diameter ca. 1.5 μm) © RUB
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The cyanobacterium Synechocystis - and with it higher plants - has three genes in advance for a single subunit of an electron-transferring protein complex. In addition to cellular respiration, the protein complex is also important for photosynthesis. Depending on the available light, the blue-green algae can access the appropriate gene. These are just some of the key findings of an international team of scientists on the flexibility of the cyanobacterium Synechocystis in light stress.

With this strategy, it has been able to survive for 3.5 billion years by optimally adapting to changing environmental conditions, according to the researchers. Blue algae take less than 90 minutes to adapt to low or strong light. The biologists led by Professor Matthias Rögner from the Ruhr-Universität Bochum (RUB) present the results of their new study in the current issue of the "Journal of Biological Chemistry".

Cyanobacteria have "invented" photosynthesis

The cyanobacteria are used by biologists as model organisms to elucidate fundamental processes such as plant photosynthesis - the conversion of light energy into bound "chemical" energy, for example in the form of sugar or starch. Cyanobacteria are the first organisms in the Earth's history to have invented the process of water splitting that releases oxygen from sunlight about 3.5 billion years ago.

"That's why we owe it to the emergence of all 'higher' life on earth, including that of humans, " explains Rögner. "Virtually every other oxygen atom we inhale goes back to the process of water splitting by cyanobacteria."

Survival through adaptation

However, the molecular basis for the successful survival of these organisms has not been sufficiently clarified for a long time. "An important prerequisite for their robustness was certainly their simple cellular structure and their adaptability to rapidly changing environmental conditions, for example drastic changes in the supply of light, " says Rögner. He and his colleagues have now examined the example of the light supply, how the blue-green algae succeeds to adapt. display

Membrane model with photosynthetic and protein complexes

Three genes for a protein subunit

In the best characterized cyanobacterium Synechocystis PCC 6803, the researchers found three genes for a single subunit of the electron-transferring cytochrome b6f protein complex - in contrast, the blueprint of the seven other subunits of this complex is only swallowed in a single gene sselt. The complex plays a key role in blue-green algae - unlike in higher plants - both for the electron transport of photosynthesis and for the respiration of these cells and is involved in photosynthesis (resp.

Thylakoid) membrane (TM).

"Our studies on the wild-type and on specially generated mutants have shown that this" gene family "represents a precise instrument with which the cell can adapt quickly to changing light conditions, explains R gner. While Genkopie 1 is read mainly under normal light, the cell activates Genkopie 2 in strong light, which ensures its survival. This switching takes less than 90 minutes, as shown by RNA analysis.

Genkopie 3 works remotely

Genkopie 3, the least known, is obviously responsible for the regulation of these processes. Strangely enough, it is not integrated into the complex at all, but can only be found in the outer cytoplasmic membrane (CM), not in the thylakoid membrane, explains R gner.

How gene copy 3 can intervene remotely in the process is still a mystery to the researchers. With gene copy 3 alone, the cell can not survive, but without it, the regulation does not work optimally.

All three genes are needed

Overall, the results clearly show that the cell needs all three genes for optimal function, and that only this mix of genes allows rapid and efficient adaptation to short-term changes in environmental conditions - especially light R gner sums up.

While higher plants have only one gene copy for each subunit of the cytochrome b6f complex, the existence of such gene families - even in the water-splitting photosystem 2 - is certainly an essential reason for the flexibility and the survival of cyanobacteria for 3.5 billion years even under extreme conditions. "Ultimately, this has allowed evolution and change in the atmosphere of our planet since prehistoric times."

(idw - Ruhr-University Bochum, 29.10.2009 - DLO)