Microalgae, present for millions of years in all types of humid environments, have attracted the interest of scientists thanks to their great environmental adaptability. They have successfully colonized both marine and freshwater systems, from brackish water to frozen glacier water and even moist soils. In order to cope with their very hostile living conditions, some of them have specialized in the reserve storage of highly energetic molecules via the development of specific mechanisms.
Understanding their systems for producing “high value-added molecules” is crucial for the development of 3rd generation biofuels. This subject is currently being worked on by a team from Biam (CEA), in collaboration with a Korean team. These energy reserves, better known as lipid droplets (LD), are the prime site of carbon storage in the model microalga Chlamydomonas reinhardtii. Such droplets are formed in large numbers by many single-celled organisms when they are under stress.
NO LIPIDS WITHOUT STRESS...
Composed of a “neutral lipid core”, the droplet, which is formed mainly under the influence of stress, is surrounded by a simple layer of membrane lipids, which is itself encircled by proteins. When the stress disappears, the microalgae resume their growth by consuming the energy stored in the form of oils (triacylglycerols, or TAGs). In order to provide a countermeasure that will prevent the algae from degrading the valuable oils, researchers are now trying to understand this degradation process in more detail.
HOW TO PRESERVE THE LIPIDS IN THE ABSENCE OF STRESS
“To decipher this mechanism, we are studying algae that have naturally mutated and that display defects in the oil degradation process,” explains Yonghua Li-Beisson, researcher and co-author of the discovery. “The one that we identified has lost all of its degradation capacities. In our research we were able to demonstrate that this phenomenon is linked to the absence of a giant protein called DTH1 (Delayed in TAG Hydrolysis 1).”
DTH1 is situated on the lipid droplet via an anchoring that binds it to a specific phospholipid (phosphatidylethanolamine). “This entire assembly contributes to the degradation phase of the droplet,” notes Yonghua. “The mutant, which we have named “dth1”, is totally lacking in this. It is therefore unable to degrade the oils, outside of periods of stress, nor does it stimulate the growth of the algae.”
A novel protein essential for the degradation of lipid droplets has thus be identified. This study opens up new perspectives in the development of 3rd generation biofuels.
| Biam (Bioscience and Biotechnology Institute of Aix-Marseille), CEA |
Pohang University of Science and Technology, Korea
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University of Technology, Dalian, China
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The Chinese University of Hong Kong, China
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