Exploration of microbial diversity from extreme environments

Scientific objectives for 2008-2011

During the last 15 years, a lot of work have been done, based on samples collected from deep-sea hydrothermal vents, in order to isolate and characterize numerous new thermophilic and hyperthermophilic species belonging to Archaea and Bacteria domains. These species are involved in biogeochemical cycles according to the electrons donors an acceptors they use. In addition to cultural approaches, molecular analysis of samples from deep sea vents chimneys evidenced an astonishing diversity. Detected phyla contain already cultivated and identified species but also numerous uncultivated species among which some belong to phyla characterized only by environmental sequences. Most often in that case, their function in the ecosystem is unknown and cannot be inferred from sequences.

The microbial diversity of deep sea hydrothermal vents is still under investigation and far from being well characterized. We plan to focus on a number of selected questions in order to improve the knowledge relative to the functioning of vent ecosystems.

 

Four questions have been selected ( cf. publications )

  • Microbes involved in carbon cycle in chemosynthetic environments; 
  • Microbes associated with the vent shrimp  Rimicaris exoculata,  whose abundance on some chimneys located on the Mid-Atlantic  Ridge is still a matter of debate; 
  • Microbial mats, very often abundant on the substratum, sometime associated with bivalves communities and mostly  uncharacterized; 
  • Mobile genetic elements (plasmids and viruses) 

European continental margins range from Arctic Ocean to the South of Spain along 15 000 km, and from East to West Mediterranean Sea at depths from 200 to 4 000 m. Continental margins host energy, living and mineral resources, some of them already under exploitation. Extremely diversified ecosystems can also be found: anoxic sediments, cold seeps, gas hydrates, deep-sea brines, etc. Our work is mainly dedicated to resource evaluation, ecosystem functioning and more specifically to the carbon cycle and microbial diversity though culture and molecular methods. A special attention is put on microbes responsible of methane production and degradation.

The discovery during the past 15 years of the subterranean biosphere, notably within ocean plates, strongly suggested that our understanding of biosphere had to be radically reconsidered. In this field of research, samples come most often from international projects like ODP and IODP. Analyses have largely demonstrated that microbial densities are not negligeable and decrease with depth up to several hundreds of meters. More specifically during the last period we analysed samples from ODP leg 190 and leg 210, ODP.

Location of field studies     

The LM2E (UMR 6197) will continue its exploration of microbial diversity on deep-sea vents in the Atlantic and the Pacific oceans. This will include the analysis of samples collected during the previous cruises in 2005, 2006 and 2007 in the Atlantic Ocean (EXOMAR 2005, MoMARETO 2006, SERPENTINE 2007, MoMARDREAM/NAUT 2007).

In the Atlantic Ocean, the Azores will be central to our investigation plan, considering the MoMAR project. The Lucky Strike hydrothermal field is known to be rich in microbial mats. The Rainbow and Ashadze sites have a special interest due to their ultramafic environments. In the Pacific Ocean, our laboratory (Daniel Prieur, Chief scientist and Anne Godfroy co-chief ) will organize the BIG oceanographic cruise in the Guaymas Basin. The specific interest there is directly linked to the fact that hydrothermal fluids are chemically enriched during their migration through the various layers of sediments and that hydrothermal vents and cold seeps can be compared.

For continental margins, our investigations will be part of the EU HERMES project to which we participate. In addition to the VIKING cruise conducted in 2006 off the Norvegian Sea and whose samples are under analysis till 2008, the MEDECO cruise (October-November 2007) allowed us to collect samples from various sites: mud volcanoes and cold seeps in East Mediterranean Sea. For the future, besides the HERMES project limited to European seas, we intend to investigate other sites located off the coasts of Zaire already partially explored during previous projects (Zaiango, REGAB site).

Deep biosphere investigations require means and equipments operated by the international consortium IODP and the European ECORD project and more specifically drilling vessels (Joides resolution and Chikyu). We plan to apply to different projects and to contribute to answer to some of the key questions in this field.