Connectivity between 'ancient' and 'modern' hypersaline environments, and the salinity limits of life

Halophilic microbes, particularly haloarchaea, are consistently cultivated from salt deposits. Based on published metabolic rates in the deep subsurface we show that co-deposited organic matter, consisting mainly of microbial cells, would provide sufficient carbon and energy to allow haloarchaea trapped inside the fluid inclusions of salt crystals to survive over millions of years. In addition, the ingress and/or redistribution of brine in salt deposits may provide new nutrient sources to starved microbes. The continuing post-depositional activities of such microbes must be considered when interpreting geochemical data from salt crystals. Moreover, the return of microbes and their genetic material into the wider environment (as a result of tectonic activity, mining operations and dissolution) after millions of years of separation will have important evolutionary consequences.