Thermoproteati

Lore & Background

Thermoproteati encompasses several phyla, including Aigarchaeota, a phylum proposed from the genome of the candidate species 'Candidatus Caldiarchaeum subterraneum' found deep within a gold mine in Japan. Genomic sequences of this group have also been found in geothermal environments, both terrestrial and marine. Another phylum, Nezhaarchaeota, was discovered in Jinze Hot Spring, Yunnan, China. The best-known edge is Thermoproteota (formerly Crenarchaeota), the most abundant archaea in the marine ecosystem, previously called sulfobacteria due to their dependence on sulfur and important as carbon fixers.

Reader's Guide

Thermoproteati holds a pivotal role in evolutionary biology due to its proposed relationship with eukaryotes. The eocyte hypothesis, proposed in the 1980s by James Lake, suggests that eukaryotes emerged within the prokaryotic eocytes, a group now encompassed by Thermoproteati. One piece of evidence supporting a close relationship between Thermoproteati and eukaryotes is the presence of a homolog of the RNA polymerase subunit Rbp-8 in Thermoproteota but not in 'Euryarchaea.' This suggests that key molecular machinery linking archaea to eukaryotes originated within this kingdom. The classification of Thermoproteati has been subject to revision; it has been proposed that the kingdom be classified as 'Crenarchaeota' and that the traditional Crenarchaeota (Thermoproteota) be reclassified as a class called Sulfolobia, along with other phyla with class rank or order. After including the kingdom category into the International Code of Nomenclature of Prokaryotes (ICNP), the only validly published name of this group is kingdom Thermoproteati (Guy and Ettema 2024). Its members occupy a wide range of ecological niches, from hyperthermophiles in hydrothermal vents to mesophiles and psychrophiles, and are predominantly anaerobic and chemosynthetic, making them key players in global biogeochemical cycles.

Did You Know?

• Thermoproteati is also known by the acronym 'TACK,' which stands for Thaumarchaeota, Aigarchaeota, Crenarchaeota, and Korarchaeota.
• The phylum Aigarchaeota was proposed from the genome of a candidate species found deep within a gold mine in Japan.
• Thermoproteota (formerly Crenarchaeota) is the most abundant archaea in the marine ecosystem and were previously called sulfobacteria.
• A homolog of the RNA polymerase subunit Rbp-8 is present in Thermoproteota but not in 'Euryarchaea,' supporting a close relationship with eukaryotes.