The genus
Aquifex is an obligately chemolithotrophic and autotrophic hyperthermophile and is the most thermophilic of all known
Bacteria. Various
Aquifex species utilize H
2, S
0, or S
2O
32- as electron donors and O
2 or NO
3- as electron acceptors and grow up to 95°C (optimum, 85°C). Only very low O
2 concentrations are tolerated by
Aquifex, but it remains one of the few aerobic bacterial hyperthermophiles known. Nutritional studies of
Aquifex species have shown them totally unable to grow chemoorganotrophically on organic compounds including complex mixtures like yeast or meat extract.
Hydrogenobacter, a relative of
Aquifex, shows most of the same properties as
Aquifex but is an obligate aerobe.
Autotrophy in
Aquifex is supported by enzymes of the reverse citric acid cycle, a series of reactions previously found only in
green sulfur bacteria within the domain
Bacteria. The complete genome of
Aquifex aeolicus has been determined and its entirely chemolithotrophic/autotrophic lifestyle is supported by an amazingly small genome of only 1.55 megabases (one-third the size of the
E. coli genome).
Taken from the text Brock Biology of Microorganisms (10th ed.). Madigan, M.T., Martinko, J.M., and Parker, J. 2003. Prentice Hall. 442p.