Buried Alive: Microbes from Ancient Halite

Halite is one of the most extreme environments to support life. From the drought of the Atacama Desert to salt deposits up to Permian in age and 2000 meters in burial depth, live microbes have been found. Because halite is geologically stable and impermeable to ground water, the microbes allegedly have a syndepositional origin, making them the oldest organisms known to live on Earth. Recently, our understanding of the microbial diversity inside halite has broadened, and the first genome sequences of ancient halite-buried microbes are now available. The secrets behind prolonged survival in salt are also starting to be revealed.

TrendsThe first genome sequences of cultivable halite-buried microbes have become available. Most of the genes are highly homologous to those in contemporary halophiles.Among cultivated halite-buried microbes, archaea belonging to Halobacterium and Halococcus are common, whereas bacteria are rare. Ribosomal 16S data has revealed many bacteria and unknown archaea in the sediments.Some halophilic archaea form miniaturized spore-like cells inside halite.Polyploidy has been observed in halite-buried and contemporary halophilic archaea. Polyploid microbes are efficient in DNA maintenance, which is beneficial for prolonged survival.Closely related isolates are found in ancient halite and contemporary hypersaline environments. Microbes in halite are likely to contribute to halophilic surface flora, explaining the similarities.