A phylogenetically distinct line of
Archaea contains three thermophilic and extremely acidophilic prokaryotes,
Thermoplasma,
Ferroplasma, and
Picrophilus.
These organisms are among the most acidophilic of all known prokaryotes and, in the case of
Picrophilus, even capable of growth below pH 0.
They also form their own order of prokaryotes with the
Euryarchaeota, the
Thermoplasmatales.
Taken from the text Brock Biology of Microorganisms (10th ed.). Madigan, M.T., Martinko, J.M., and Parker, J. 2003. Prentice Hall. 456p.