 "A. aeolicus" needs oxygen at concentrations higher than 7.5 p.p.m to perform respiration while "A. pyrophilus" is capable of respiration with nitrogen however, both species have a nitrate reductase and nitrate transporter genes located within their genome.the enzymes used in other bacterium for oxygen respiration are used by "Aquifex".Many other oxidoreductases are present however their physiological role is unknown.