Thermococci

Thermococci is a class of extremophilic archaea within the phylum Euryarchaeota. Members are among the most thermophilic microorganisms, typically thriving at high temperatures and often found in environments such as deep-sea hydrothermal vents and hot springs. They are usually anaerobic or microaerophilic and rely on organic substrates for energy, frequently reducing sulfur compounds as electron acceptors and producing hydrogen gas as a byproduct.

Physiology and metabolism: Thermococci are predominantly chemoorganotrophs, utilizing peptides or carbohydrates to fuel growth. Many species are sulfur-dependent, using elemental sulfur or thiosulfate in their energy metabolism. They possess thermostable enzymes and membrane systems suited to high-temperature life, and their cell envelopes reflect archaeal lipid chemistry. Some members can ferment substrates in the absence of sulfur, reflecting metabolic versatility under extreme conditions.

Ecology and distribution: Members of Thermococci populate high-temperature ecosystems around the world, including submarine volcanic regions and geothermal springs. In these habitats, they contribute to the sulfur and hydrogen cycles and form part of complex vent-associated microbial communities.

Taxonomy and notable members: Thermococci is a class within Euryarchaeota, comprising the order Thermococcales. Within this order, families include Thermococcaceae and Pyrococcaceae, with well-known genera such as Thermococcus and Pyrococcus. Thermococcus kodakarensis is a widely used model organism for studying archaeal biology, metabolism, and thermostable enzymes.

Significance: The study of Thermococci informs understanding of life at extreme temperatures, archaeal biochemistry, and the evolution of hyperthermophily. Enzymes from these organisms have industrial relevance due to their stability under high heat.