Archaea can live in the most extreme places are often classified according to the environments in which they live: Halophiles are salt-loving, Thermophiles live in extremely high temperatures, Psychrophiles live in extremely cold temperatures and Methanogens are anaerobic and produce methane gas.  They can be found from the frozen Artics/Antarchtics to the boiling acidic springs in Yellowstone and the deep hydrothermal vents in the oceans. 

Most of the culturable and well know species can be divided into the two main phyla:

• Phylum Crenarchaeota  – most abundant marine archaea, originally isolated from geothermally heated sulfuric springs in Italy, and includes thermophiles, hyperthermophiles and thermoacidophiles (eg. Sulfolobus, found in hot springs).
• Phylum Euryarchaeota  – includes methanogens, halophiles and thermophiles. They are also found in more moderate environments (eg. Methanobrevibacter smithii, helps remove excess hydrogen from the human gut).

Other grouping has been suggested as new species are discovered. There is still a lot to be discovered about these ancient organisms. 

Sulfolobus is one of the archaea genus most often isolated and most well known by scientists. It is found in sulphuric hydrothermal areas where it oxidises sulphur into sulphuric acid, helping to dissolve the rocks into mud¹.

It has also been suggested that many viruses would exist in Yellowstone’s hydrothermal features as they would be a logical part of the thermophilic ecosystem. Research on Sulfolobus in Congress Pool, at Norris Geyser Basin, found that it was infected by one such virus^2,3.

---

References

1. Thermophilic Archaea
2. Thermophilic Viruses
3. Rebecca Hochstein et al, Structural studies of Acidianustailed spindle virus reveal a structural paradigm used in the assembly of spindle-shaped viruses, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073/pnas.1719180115