Halophilic microorganisms

In response to the environmental context concerning the depletion of fossil energy reserves, the accumulation of anthropogenic pollutants and their impact on global change, the 21st century is moving strongly towards the development of biotechnologies aimed at adding value to organisms or compounds derived from biological resources. The valorization of renewable resources of biological origin, independently of the petrochemical industry, is now widely democratized.

The discovery of extremophilic microorganisms and their original properties has raised hopes for research, industrial and biotechnological applications. Although so-called extreme environments are hostile to human life, they are colonized by adapted extremophilic microorganisms. Several extreme conditions may coexist, in which case the micro-organisms are poly-extrêmophiles. The first known extremophiles are halophiles, or "salt-loving" organisms. They were discovered in hypersaline environments. Hypersaline environments are extreme because salt concentrations are higher than in seawater, and can sometimes reach saturation in certain lakes, deserts or basins. There are many hypersaline environments on the earth's surface: the Dead Sea, the Great Salt Lake, the Salar d'Uyumi, salt marshes, hypersaline underwater basins, etc.

Every living cell is immersed in a saline solution containing mainly sodium chloride (NaCl) and an equivalent concentration of potassium chloride (KCl). A cell's vital functions are closely linked to the concentrations of NaCl and KCl on either side of the cell membrane. At low concentrations, salt is essential for cell function. At high concentrations, however, salt can prevent life, since a significant difference in salt concentration between the internal and external environments causes water to escape. Surprisingly, ultrasaline environments are not sterile. In fact, so-called halophilic microbial communities proliferate in habitats where salts (essentially NaCl and MgCl ₂ ) have been concentrated to the limit of their solubility (5 to 6 molar), i.e. more than ten times the concentration in seawater. These microbes are the only form of life possible in the large salt lakes or salt marshes of the French coastline. Yet halophilic micro-organisms are a source of biomolecules with varied and original functions, properties and structures, which are exploited in numerous biotechnological applications and are, for the most part, part of our daily lives.

Industrial biotechnology developed substantially when it was necessary to replace the petroleum-based chemical industry. However, the production costs of biological resources such as bioplastics, biofuels and biochemical compounds remain extremely high compared with the...