Deep sea biosphere represents the largest ecosystem on earth. It is characterized by extreme physical and chemical conditions and especially by high hydrostatic pressures. Even though ocean depths (cold / hot) harbour a wide community of prokaryots with different metabolic traits within the two domains of life (Bacteria & Archaea), only a few of them are piezophiles up to strict piezophiles. Let's now have a closer look on how the LM2E explores those mechanisms of adaptation.
Piezophily in microorganisms
Among the fifty piezophiles isolated so for, more than 88% are psychrophiles. The LM2E has largely contributed to the isolation of hyper/thermophilic procaryotic piezophiles. In 1999, the lab isolated the piezophilic hyperthermiphilic archea Thermococcus barophilus (optimal growth temperature at pressures over 1 atmosphere). In 2002, our team isolated in pure culture the first thermophilic and piezophilic bacteria Marinitoga piezophila. Finally, in 2009, we isolated the only strict piezophilic hyperthermophilic archea known to date : Pyrococcus yayanosi CH1 (organism incapable to grow at atmospheric pressure). The presence of piezophilic procaryotes in such cold and hot environments suggest the following questions :
- Do piezophilic prokaryotes have particular metabolisms and physiological features that lead them to play a key role in geochemical cycles of deep sea enviroments ?
- Are piezophiles autochthonous or colonizers ? What are the evolutionary and adaptative processes that lead prokaryotes to migrate from ocean surface down to deep sea floor or the reverse ?
- Does piezophilic andnon-pizeophilic ecosystems coexist in deep sea ocean ? If yes, which ones are the most active ?
To answer all those questions, several biological approaches are needed (comprising microbial ecology, meta/omics, genetics, physiology, biochemistry, etc). This implies together the development of instruments rendering possible the study of microorganisms of deep sea biosphere to closely mimic the extreme conditions observed at the deep sea floor. Those scientific challenges leads the lab to active collaborations strategies at national and international levels.
Metabolic pathways of piezophily
At the national level, the LM2E pilots the ANR project n°10-BLAN-1725 01 (2010-2014) untitled "Genomic and molecular basis of piezophily in Pyrococcus yayanosii CH1, a strict piezophile" in partenership with Joseph Zaccai (DR CNRS, ILL Grenoble), Vincent Daubin (CR CNRS LBBE Lyon), Philippe Oger (CR CNRS, ENS-Lyon) et Bruno Franzetti (DR CNRS, IBS, Grenoble).
Our transcriptomic and proteomic approaches have demonstrated that expression of a set of genes together with the syntesis of their corresponding proteins are modulated by the variations of hydrostatic pressures in T. barophilus and other piezophilic Archae. More precisely, this study has already clearly identified physiological targets such as the metabolism of particular sugars and amino-acids, the biosynthesis of hydrogen and ATP, etc.
Genetic tools for thermo/piezophiles
In order to improve our knowledge over the mecanisms of adaptation to hydrostatic pressure among piezophilic hyperthermophilic Archae, it is required to use a genetic approach in complement to the ones abovementionned, i.e. genomics, transcriptomics and proteomics. For that reason, the LM2E has developed genetic tools and obtained transformation protocols for the hyperthermophilic piezophile archea Thermococcus barophilus. Results obtained are really promising and have already demonstrated that we are now able to run genetic manipulation in an extremophilic Archea. The latters consitutes a major advance in the domain and opens new perspectives for a better understanding of the adapation mecanisms to high hydrostatic pressures.
Along side with this fundamental point of view, this genetic tool will open the way to other opportunities for applications such as :
- The overexpression of hyperthermophilic proteins difficult to obtain by standard production protocols - in Escherchia coli for example.
- The use of this model from deep sea for synthetic biology.
This research axis needs also several technological development of instruments that offers the possibility to mimic the extreme conditions from deep sea. In close collaboration with the HP Systems society, the LM2E has developed a prototype of hyperbaric bioreactor for continuous culture (funded by UBO/CNRS/ANR Living Deep). LM2E has thus a unique tool capable to simulate various deep sea conditions (cold / hot), a key step to try to isolate new microorganisms and to run studies about microbial communities from those particular environments (ex : hydrothermal vents, etc).