While testing a new camera, I recently collected some photographs of the haloarchaeon Haloferax volcanii within salt crystals that had formed in a 6 well culture dish. These formations are halite or rock salt, a mineralized form of salt left behind as water evaporates.
High levels of salt are toxic to most forms of life. For example, seawater has a salt concentration between 3% and 4% and human blood contains just 0.9% salt. Many microbial species including some bacteria and algae live at elevated salt concentrations, within brines from 5% to about 15% salt. But there is only one microbial group that tolerates and in fact often thrives at very high salt concentrations: the haloarchaea.
Haloarchaea are found in bodies of water like the Dead Sea and the Great Salt Lake, in sub-terrain salt deposits, within evaporation ponds at sea salt production facilities, and at other sites where salt concentrations exceed 20% or even 30%. Even when all of the water evaporates, leaving behind only precipitated halite, haloarchaeal cells often remain living, held up in fluid inclusions within the salt crystals themselves. Remarkably, a recent culture-independent study supported earlier culture based isolation experiments suggesting that haloarchaeal species can be recovered from ancient halite deposits, persisting for thousands or even millions of years.
More of Hfx. volcanii with salt crystals: