Acidianus

Acidianus is a genus of thermoacidophilic archaea in the order Sulfolobales. Members are adapted to hot, acidic environments and are commonly found in volcanic hot springs, fumaroles, and acidic hydrothermal vents. They are typically chemolithoautotrophs that obtain energy from the oxidation of reduced sulfur compounds and fix carbon dioxide, though some species can also utilize organic substrates under certain conditions.

Physiology and metabolism: Acidianus species thrive at high temperatures and low pH, often growing best at temperatures above 60°C and pH values well below neutral. Their sulfur-based metabolism enables growth in sulfur-rich environments, with some species capable of oxidizing elemental sulfur and sulfide to sulfate. The organisms possess cell envelopes characteristic of archaea in the Sulfolobales, and cell shapes range from irregular coccoid to short rod forms in different species. Motility and surface structures vary among members, contributing to colonization of sulfur-rich substrates.

Ecology and distribution: In their natural habitats, Acidianus contribute to sulfur cycling within geothermal ecosystems. Their presence reflects the interaction of geothermally heated water, acidity, and reduced sulfur compounds that shape microbial communities in these extreme environments. The genus illustrates how life can conquer dual limits of heat and acidity.

Taxonomy and species: The genus comprises several described species, including Acidianus brierleyi and Acidianus manzaensis, among others identified from geothermal regions around the world. As archaeal taxonomy evolves with new phylogenetic data, the precise circumscription of Acidianus within Sulfolobales has been refined, but it is generally recognized as a thermoacidophilic archaeal lineage.

See also: Sulfolobales, extremophiles, archaeal sulfur metabolism.