Thermoproteia

Thermoproteia, Crenarchaeota, Thermoprotei, Sulfolobia, called, crenarcheas, eocytes, sulfobacteria or crenotae is a class of archaea, formerly classified as a phylum, however the term Crenarchaeota may be used to refer to all TACK or Thermoproteota archaea. Initially it was thought to include only hyperthermophilic organisms, often sulfur-dependent chemosynthesizers. However, recent studies have identified them as the most abundant archaea in the marine ecosystem. Crenarchaeota is one of the two main groups of archaea and was originally separated from the other group (Euryarchaeota) based on rRNA sequences. This division has been supported by some physiological characteristics, such as the lack of histones. (However, some species of Crenarchaeota have been found to possess histones.)

Unlike other groups of organisms, Crenarchaeota have been found to have a unique cell division machinery.

Classification

We can distinguish two groups of crenarcheas:

Hyperthermophiles

This group (orders Thermoproteales, Sulfolobales, Thermofilales) includes the species with the highest growth temperatures of any known organism. Optimum growth is between 75 and 105 °C, while the maximum growth temperature to grow Pyrolobus is as high as 113 °C. Most of these species cannot grow below 70 °C, although they can survive for long periods at low temperatures. Some species are acidophilic with an optimum pH between 1.5 and 4 and die at pH 7, while others are neutrophilic or slightly acidophilic, growing optimally at pH 5.5–7.5. They are found in volcanic habitats such as continental hot springs and deep-sea hydrothermal vents, shallow or deep.

The metabolic modes are diverse, ranging from chemoorganotrophs to chemolithotrophs. Aerobic chemolithotrophs obtain energy by the oxidation of various sulfuric compounds, hydrogen, or ferrous iron, while anaerobic chemolithotrophs reduce sulfur, thiosulfate, or produce nitrates, hydrogen sulfide, or ammonia. Chemoorganotrophs grow on complex organic substrates, sugars, amino acids, or polymers. Several species are primary producers using carbon dioxide as the sole carbon source and obtaining energy by oxidation of inorganic substances such as sulfur or hydrogen, or by reduction of sulfur or nitrate.

One of the best known species of Crenarchaeota is the Sulfolobus solfataricus. This organism was originally isolated from samples taken from sulfuric geothermal springs in Italy and grows at 80 °C and pH 2-4. Species of the same genus have since been found throughout the world. Unlike the vast majority of cultivated thermophiles, this species can grow aerobically and using organic energy sources such as sugar. These factors make it much easier to culture than anaerobic organisms and have led Sulfolobus to become a model organism for the study of hyperthermophiles and a large group of viruses that are develop within them.

Mesophiles and psychrophiles

Recent environmental analyzes based on rRNA sequences indicate that Crenarchaeota is also widely distributed in low-temperature environments such as soils, sediments, freshwater, and oceans.^, Although none have been able to be cultivated, the obtaining environment (together with the genomic data) suggests that they are mesophilic or psychrophilic organisms. This large group of archaea appears to derive from thermophilic ancestors that invaded various low-temperature habitats.

Perhaps most astonishing is their high relative abundance in winter surface waters in Antarctica (-1.8 °C), where they make up as much as 20% of the total microbial rRNA. Similar examinations in temperate waters off the California coast show that these organisms tend to be most abundant at depths less than 100 m. Based on these measurements, it appears that these organisms are very abundant in the ocean and would be one of the main contributors to carbon sequestration. This, together with the fact that Crenarchaeota rRNA sequences have been found in every low-temperature habitat in which they were searched, suggests that they may be globally distributed and play an important role in the biosphere.

Cladogram

A somewhat agreed phylogeny in the GTDB database and the Annotree is the following: