Life in Hypersaline Environments

Abstract

Many microorganisms are adapted to life at high-salt concentrations. Halophilic representatives are found in each of the three domains of life: Archaea, Bacteria, and Eukarya. Halophilic viruses exist as well. In NaCl-saturated brines such as found in the northern part of Great Salt Lake, Utah, in a few other natural salt lakes, and in saltern crystallizer ponds for the production of salt, we find members of all groups. Blooms of microorganisms have occasionally been observed in the magnesium- and calcium-rich waters of the Dead Sea. Dense communities of extremely halophilic Archaea (family Halobacteriaceae) and of the alga Dunaliella salina often impart a red color to salt-saturated brines. There are different strategies that enable halophilic or halotolerant microorganisms to grow in the presence of high-salt concentrations. A few groups (Archaea of the family Halobacteriaceae; the red extremely halophilic bacterium Salinibacter) maintain molar concentrations of salts (K+, Cl−) intracellularly, and their proteins are functional in a high-salt environment. Other groups (most salt-adapted members of the Bacteria, halophilic algae, and fungi) accumulate organic solutes to provide osmotic balance of their cytoplasm with the hypersaline medium.