MEB - Topic 3

Ecology and physiology of microorganisms in extreme conditions

 

Moderator : Gael Erauso

 

We are interested in procaryotes referred to extremophiles because they proliferate under physico-chemical conditions (temperature, pH, salinity, pressure, ionizing radiation) or biological (energy source) close to the limits of life on Earth. Their natural living environments include:

  1. marine hydrothermal systems associated with volcanic activity (hot springs, "black smokers") or other geological processes such as serpentinization;
  2. lakes with continental brines (Tunisian chotts) or underwater lakes (DHAB in the Mediterranean);
  3. oceanic sub-surface which might represent the largest microbial compartment on Earth,
  4. deep oceanic domain that accounts for 80% of the hydrosphere.

These environments are considered extreme for one or more factors: pH between 2 and 4, temperature (which can vary from 2°C to more than 110°C in the hydrothermal systems), hydrostatic pressure (average depth of the oceans is 3850m corresponding to an hydrostatic pressure of 38.5 MPa). The prokaryotes that develop there are therefore multi-extremophiles (acidophile-thermophile-piezophile-psychrophile).

Our main goals are :

  • to explore the specific and functional diversity of prokaryotes (and associated viruses);
  • to understand the functioning of these ecosystems;
  • to apprehend the biological processes allowing these extremophiles to live at the limits of life.

Our methodological approaches are multidisciplinary ranging from biogeochemistry to (meta) genomics. They are developed during sampling campaigns using in situ conditions, or in the laboratory using culture of model study organisms, or in silico during bioinformatic analysis of NGS sequencing data.

 

Examples of studies

 

Degradation of organic matter at high hydrostatic pressure

CTD carousel with High Pressure Sampler Unit (HPSU) for collecting seawater samples under in situ conditions of hydrostatic pressure.

 

 

The MIO-HPLab, mobile hyperbaric laboratory to study the deep oceanic domain.

 

 

Response of sulfate-reducing bacteria to the hydrostatic pressure

 

We study the mechanisms of adaptation to hydrostatic pressure of sulfate-reducing microorganisms (e.g., Desulfovibrio sp.) Isolated from deep marine environments (ie, hydrothermal vents, wood falls). We are working on determining their ability to grow at different pressures, using culture systems in hyperbaric conditions (up to 40 MPa). We are using global approaches as genomics, proteomics, and transcriptomics to identify the factors of this adaptation. In addition, biochemical, enzymatic and molecular genetic techniques allow us to study more specifically some of these factors.

Hydrothermal and hypersaline systems