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Archaea were initially classified as bacteria, receiving the name archaebacteria (/ ˌ ɑːr k i b æ k ˈ t ɪər i ə /, in the Archaebacteria kingdom), but this term has fallen out of use. [5] Archaeal cells have unique properties separating them from Bacteria and Eukaryota. Archaea are further divided into multiple recognized phyla.
Pyrococcus furiosus is a strictly anaerobic, heterotrophic, sulfur-reducing archaea originally isolated from heated sediments in Vulcano, Italy by Fiala and Stetter. It is noted for its rapid doubling time of 37 minutes under optimal conditions, meaning that every 37 minutes the number of individual organisms is multiplied by two, yielding an exponential growth curve.
Three of the Pyrococcus species have been sequenced.P. furiosus is the largest containing 1.9 Mb followed by P. abyssi with 1.8 Mb and P. horikoshii with 1.7 Mb. [citation needed] The genomes encode for many different metabolic enzymes which gives themselves a wider spectrum of living conditions because they can transport and metabolize a wide range of organic substances.
The three-domain system adds a level of classification (the domains) "above" the kingdoms present in the previously used five- or six-kingdom systems.This classification system recognizes the fundamental divide between the two prokaryotic groups, insofar as Archaea appear to be more closely related to eukaryotes than they are to other prokaryotes – bacteria-like organisms with no cell nucleus.
The term "bacteria" was traditionally applied to all microscopic, single-cell prokaryotes. However, molecular systematics showed prokaryotic life to consist of two separate domains, originally called Eubacteria and Archaebacteria, but now called Bacteria and Archaea that evolved independently from an ancient common ancestor. [5]
Methanobrevibacter smithii is the predominant methanogenic archaeon in the microbiota of the human gut. [1] M. smithii has a coccobacillus shape.It plays an important role in the efficient digestion of polysaccharides (complex sugars) by consuming the end products of bacterial fermentation (H 2, CO 2, acetate, and formate). [2]
Euryarchaeota (from Ancient Greek εὐρύς eurús, "broad, wide") is a kingdom of archaea. [3] Euryarchaeota are highly diverse and include methanogens, which produce methane and are often found in intestines; halobacteria, which survive extreme concentrations of salt; and some extremely thermophilic aerobes and anaerobes, which generally live at temperatures between 41 and 122 °C.
Lokiarchaeota is a proposed phylum of the Archaea. [1] The phylum includes all members of the group previously named Deep Sea Archaeal Group, also known as Marine Benthic Group B. Lokiarchaeota is part of the superphylum Asgard containing the phyla: Lokiarchaeota, Thorarchaeota, Odinarchaeota, Heimdallarchaeota, and Helarchaeota. [2]