Picrophilus torridus

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Picrophilus torridus is a tiny archaeon that was described in 1996. It was found in soil near a hot spring in Hokkaido, Japan, where the soil was extremely acidic (pH below 0.5). It has one of the smallest genomes known among free-living, non-parasitic organisms, with most of its genes coding for proteins (high coding density). Scientists think that the combination of high temperature and very low pH in its environment pushed evolution toward a small, compact genome that is less likely to be damaged by harsh conditions.