Aquifex

Aquifex is a microorganism, bacterium, one of the few in the phylum Aquificae. The two species generally classified in Aquifex are A. pyrophilus and A. aeolicus. Both are hyperthermophilic, growing best in water temperatures of 85 to 95°C. They often grow near underwater volcanoes or hydrothermal vents. A. aeolicus was discovered in northern Sicily, while A. pyrophilus was first found in northern Iceland. They are true bacteria (of the Bacteria domain) unlike other inhabitants of extreme environments, the Archaea.

Both species of Aquifex are rod-shaped with a length of 2 to 6 µm and a diameter of about 0.5 µm. They are Gram-negative autotrophs and do not form spores. Aquifex is Latin for producer of water, which refers to the fact that their method of respiration produces water by oxidizing hydrogen, thiosulfate, and sulfur with oxygen as the acceptor.

Aquifex tends to form cell aggregates consisting of up to 100 individual cells. A. aeolicus requires oxygen to survive, but can grow in oxygen levels as low as 7.5 PPM. A pyrophilus can even grow anaerobically by reducing nitrogen instead of oxygen. Like other thermophilic bacteria, Aquifex has important applications in industrial processes.

The genome of A aeolicus has been sequenced.^, This was made relatively easy by the fact that the genome length is only about one third that of E. coli. Comparison of the A aeolicus genome with that of other organisms revealed that around 16% of its genes come from the Archaea domain. It is believed that this genus may be one of the earliest in the bacterial domain.