Crenarchaeota is a class of Archaea that is extremely diverse, containing genera and species that differ vastly in their morphology and requirements for growth. All Crenarchaeota are aquatic organisms, and they are thought to be the most abundant microorganisms in the oceans. Most, but not all, Crenarchaeota are hyperthermophiles; some of them (notably, the genus Pyrolobus) are able to grow at temperatures up to 113 °C.
Archaea of the genus Sulfolobus are thermophiles that prefer temperatures around 70–80°C and acidophiles that prefer a pH of 2–3. Sulfolobus can live in aerobic or anaerobic environments. In the presence of oxygen, Sulfolobus spp. use metabolic processes similar to those of heterotrophs. In anaerobic environments, they oxidize sulfur to produce sulfuric acid, which is stored in granules. Sulfolobus spp. are used in biotechnology for the production of thermostable and acid-resistant proteins called affitins. Affitins can bind and neutralize various antigens (molecules found in toxins or infectious agents that provoke an immune response from the body).
Another genus, Thermoproteus, is represented by strictly anaerobic organisms with an optimal growth temperature of 85 °C. They have flagella and, therefore, are motile. Thermoproteus has a cellular membrane in which lipids form a monolayer rather than a bilayer, which is typical for archaea. Its metabolism is autotrophic. To synthesize ATP, Thermoproteus spp. reduce sulfur or molecular hydrogen and use carbon dioxide or carbon monoxide as a source of carbon. Thermoproteus is thought to be the deepest-branching genus of Archaea, and thus is a living example of some of our planet’s earliest forms of life.
Parker, N., Schneegurt, M., Thi Tu, A.-H., Forster, B. M., & Lister, P. (n.d.). Microbiology. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/microbiology