"Aquifex aeolicus" is a chemolithoautotrophic, Gram-negative, motile, hyperthermophilic bacterium. "A. aeolicus" is generally rod-shaped with an approximate length of 2-6 μm and a diameter of 0.4-0.5 μm. "A. aeolicus" is neither validly nor effectively published and, having no standing in nomenclature, should be styled in quotation marks. It is one of a handful of species in the Aquificota phylum, an unusual group of thermophilic bacteria that are thought to be some of the oldest species of bacteria, related to filamentous bacteria first observed at the turn of the century. "A. aeolicus" is also believed to be one of the earliest diverging species of thermophilic bacteria. "A. aeolicus" grows best in water between 85 °C and 95 °C, and can be found near underwater volcanoes or hot springs. It requires oxygen to survive but has been found to grow optimally under microaerophilic conditions. This can be useful for improving industrial processes.
Metabolism
As an autotroph, "A. aeolicus" has the ability to obtain all necessary carbon by fixing CO<sub>2</sub> from the environment and utilizes molecular hydrogen as an electron/energy source. It is hypothesized that this is possible because 1) their oxygen-respiration system was already highly developed before the advent of oxygenic photosynthesis, 2) the Aquifex lineage came to life after there was a rise in atmospheric oxygen, or 3) oxygen respiration was developed, and then transferred among different bacterial lineages, such as Aquifex.