Sulfolobales

Sulfolobales is an order of archaea within the class Thermoprotei, in the phylum Thermoproteota. Members are extremophiles, typically found in acidic and hot environments such as volcanic hot springs, solfataras, and other geothermal sites. They play a role in sulfur cycling in these systems and are important for studies of archaeal biology and metabolism.

Morphology and physiology. Cells in Sulfolobales are often irregularly shaped, including coccoid and rod-like forms, and may occur singly or in aggregates. They possess an S-layer–type cell envelope and rely on archaeal ether lipids. Many species are thermoacidophilic, growing best at high temperatures (often above 60°C) and low pH (often below 4). Metabolic strategies are diverse: many members are chemolithoautotrophs that derive energy by oxidizing reduced sulfur compounds, such as elemental sulfur or sulfide, with oxygen or ferric iron as electron acceptors; others are chemoorganotrophs. Some species are facultatively anaerobic and can use sulfur compounds for energy under different redox conditions. Carbon fixation commonly occurs via the 3-hydroxypropionate/4-hydroxybutyrate cycle in several genera.

Ecology and genera. Sulfolobales inhabit acidic, high-temperature environments worldwide and contribute to mineral and sulfur transformations in these ecosystems. Notable genera include Sulfolobus, Acidianus, and Metallosphaera, among others. Sulfolobus solfataricus and Sulfolobus acidocaldarius are well-studied model organisms for archaeal genetics and biochemistry.

Taxonomy and study. The order has been subject to reclassification as archaeal taxonomy has advanced, but Sulfolobales remains recognized as a distinct group within Thermoprotei, with ongoing research refining relationships among its members.