Phylum Korarchaea

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Obsidian Pool, Yellowstone National Park : James W. Brown

The Korarchaea are known almost exclusively from ssu-rRNA sequences from a variety of hydrothermal environments. They are probably best-known from the site of their original discovery: Obsidian Pool, in Yellowstone National Park. This anaerobic pool varies from 65°C to boiling (94°C at this altitude), pH 6.5, and is a slurry of silica, pyrite, and elemental sulfur. The exact placement of the korarchaeal branch relative to other Archaea remains uncertain; it may originate before the split separating Euryarchaea and Crenarchaea, or may be specifically affiliated with the Crenarchaea. Resolving this issue will probably require additional genome sequences. No members of this group have been grown in pure culture.

Example species : Korarchaeum cryptofilum

Korarchaeum symbiosum : Elkins, et al 2008 PNAS 105:8102

K. cryptophilum is a very thin filamentous (0.17μm x 5-100μm) thermophilic heterotrophic korarchaeote. It has not been grown in pure culture, but has been maintained in an 85°C anaerobic community culture originating from a sample from Obsidian Pool. The genome sequence of its single 1.59Mbp circular chromosome has been determined from cells physically isolated from this culture on the basis of their unusually high resistance to the detergent SDS; this resistance is presumably due to its very dense and orderly S-layer. The composition of its genome suggests that K. cryptophilum is a peptidolytic heterotroph, but unlike other peptidolytic hyperthermophilic Archaea (e.g. Pyrococcus), it seems to use only protons as the terminal electron acceptor, (generating H2), lacking the ability to use either oxygen or sulfur (or anything else) as terminal electron acceptors. The genes required for the biosynthesis of a number of cofactors/vitamins are absent; this may explain the inability of K. cryptophilum to grow in pure culture.