TheThermoproteota arearchaea that have been classified as aphylum of the domainArchaea.[2][3][4] Initially, the Thermoproteota were thought to be sulfur-dependentextremophiles but recent studies have identified characteristic Thermoproteota environmentalrRNA indicating the organisms may be the most abundant archaea in the marine environment.[5] Originally, they were separated from the other archaea based on rRNA sequences; other physiological features, such as lack ofhistones, have supported this division, although some crenarchaea were found to have histones.[6] Until 2005 all cultured Thermoproteota had been thermophilic or hyperthermophilic organisms, some of which have the ability to grow at up to 113 °C.[7] These organisms stainGram negative and are morphologically diverse, having rod,cocci,filamentous and oddly-shaped cells.[8] Recent evidence shows that some members of the Thermoproteota are methanogens.
Thermoproteota were initially classified as a part ofregnumEocyta in 1984,[9] but this classification has been discarded. The term "eocyte" now applies to eitherTACK (formerly Crenarchaeota) or to Thermoproteota.
One of the best characterized members of the Crenarchaeota isSulfolobus solfataricus. This organism was originally isolated fromgeothermally heated sulfuric springs in Italy, and grows at 80 °C and pH of 2–4.[10] Since its initial characterization by Wolfram Zillig, a pioneer in thermophile and archaean research, similar species in the samegenus have been found around the world. Unlike the vast majority of cultured thermophiles,Sulfolobus growsaerobically andchemoorganotrophically (gaining its energy from organic sources such as sugars). These factors allow a much easier growth under laboratory conditions thananaerobic organisms and have led toSulfolobus becoming a model organism for the study of hyperthermophiles and a large group of diverse viruses that replicate within them.
Irradiation ofS. solfataricus cells withultraviolet light strongly induces formation oftype IV pili that can then promote cellular aggregation.[17] Ultraviolet light-induced cellular aggregation was shown by Ajon et al.[18] to mediate high frequency inter-cellularchromosome marker exchange. Cultures that were ultraviolet light-induced had recombination rates exceeding those of uninduced cultures by as much as three orders of magnitude.S. solfataricus cells are only able to aggregate with other members of their own species.[18] Frols et al.[17][19] and Ajon et al.[18] considered that the ultraviolet light-inducible DNA transfer process, followed byhomologous recombinational repair ofdamaged DNA, is an important mechanism for promoting chromosome integrity.
This DNA transfer process can be regarded as a primitive form ofsexual interaction.
Beginning in 1992, data were published that reported sequences of genes belonging to the Thermoproteota in marine environments.[20][21] Since then, analysis of the abundantlipids from the membranes of Thermoproteota taken from the open ocean have been used to determine the concentration of these “low temperature Crenarchaea” (SeeTEX-86). Based on these measurements of their signature lipids, Thermoproteota are thought to be very abundant and one of the main contributors to thefixation of carbon .[22] DNA sequences from Thermoproteota have also been found in soil and freshwater environments, suggesting that this phylum is ubiquitous to most environments.[23]
In 2005, evidence of the first cultured “low temperature Crenarchaea” was published. NamedNitrosopumilus maritimus, it is anammonia-oxidizing organism isolated from a marine aquarium tank and grown at 28 °C.[24]
DNA analysis from 2008 (and later, 2017) has shown that eukaryotes evolved from thermoproteota-like organisms. Other candidates for the ancestor of eukaryotes include closely relatedasgards. This could suggest that eukaryotic organisms possibly evolved fromprokaryotes.
These results are similar to theeocyte hypothesis of 1984, proposed byJames A. Lake.[9] The classification according to Lake, states that both crenarchaea and asgards belong to Kingdom Eocyta. Though this has been discarded by scientists, the main concept remains. The term "Eocyta" now either refers to theTACK group or to Phylum Thermoproteota itself.
However, the topic is highly debated and research is still going on.
^Blochl E, Rachel R, Burggraf S, Hafenbradl D, Jannasch HW, Stetter KO (Feb 1997). "Pyrolobus fumarii, gen. and sp. nov., represents a novel group of archaea, extending the upper temperature limit for life to 113 °C".Extremophiles: Life Under Extreme Conditions.1 (1):14–21.doi:10.1007/s007920050010.PMID9680332.S2CID29789667.
^Zillig W, Stetter KO, Wunderl S, Schulz W, Priess H, Scholz I (1980). "The Sulfolobus-"Caldariellard" group: Taxonomy on the basis of the structure of DNA-dependent RNA polymerases".Arch. Microbiol.125 (3):259–269.Bibcode:1980ArMic.125..259Z.doi:10.1007/BF00446886.S2CID5805400.
^abFröls S, Ajon M, Wagner M, Teichmann D, Zolghadr B, Folea M, et al. (November 2008). "UV-inducible cellular aggregation of the hyperthermophilic archaeon Sulfolobus solfataricus is mediated by pili formation".Molecular Microbiology.70 (4):938–952.doi:10.1111/j.1365-2958.2008.06459.x.PMID18990182.
^abcAjon M, Fröls S, van Wolferen M, Stoecker K, Teichmann D, Driessen AJ, et al. (November 2011). "UV-inducible DNA exchange in hyperthermophilic archaea mediated by type IV pili".Molecular Microbiology.82 (4):807–817.doi:10.1111/j.1365-2958.2011.07861.x.PMID21999488.
^Fröls S, White MF, Schleper C (February 2009). "Reactions to UV damage in the model archaeon Sulfolobus solfataricus".Biochemical Society Transactions.37 (Pt 1):36–41.doi:10.1042/BST0370036.PMID19143598.
Frederiksen W, Garrity GM, Grimont PA, Kampfer P, Maiden MC, Nesme X, et al. (May 2002). "Report of the ad hoc committee for the re-evaluation of the species definition in bacteriology".International Journal of Systematic and Evolutionary Microbiology.52 (Pt 3):1043–1047.doi:10.1099/00207713-52-3-1043.PMID12054223.
Mayall BC, Gurtler V (Jan 2001). "Genomic approaches to typing, taxonomy and evolution of bacterial isolates".International Journal of Systematic and Evolutionary Microbiology.51 (Pt 1):3–16.doi:10.1099/00207713-51-1-3.PMID11211268.
Young J (May 2001). "Implications of alternative classifications and horizontal gene transfer for bacterial taxonomy".International Journal of Systematic and Evolutionary Microbiology.51 (Pt 3):945–953.doi:10.1099/00207713-51-3-945.PMID11411719.
Kohtz, Petrosian, Krukenberg, Jay, Pilhofer, Hatzenpichler (2024). "Cultivation and visualization of a methanogen of the phylum Thermoproteota".Nature.632:1118–1123.doi:10.1038/s41586-024-07631-6.PMID39048824.
Krukenberg, Kohtz, Jay, Hatzenpichler (2024). "Methyl-reducing methanogenesis by a thermophilic culture of Korarchaeia".Nature.632:1131–1136.doi:10.1038/s41586-024-07829-8.PMID39048017.
Kohtz, Nupp, Hatzenpichler (2025). "Cultivation of Methanonezhaarchaeia, the third class of methanogens within the phylum Thermoproteota".Science Advances.11: eaea0936.doi:10.1126/sciadv.aea0936.PMID41385625.{{cite journal}}: CS1 maint: article number as page number (link)
