''Thermococcus litoralis'' (''T. litoralis'') is a species of

Archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...

that is found around deep-sea

hydrothermal vents A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...

as well as shallow submarine thermal springs and oil wells. It is an anaerobic

organotroph An organotroph is an organism that obtains hydrogen or electrons from organic substrates. This term is used in microbiology to classify and describe organisms based on how they obtain electrons for their respiration processes. Some organotrophs su ...

hyperthermophile that is between in diameter. Like the other species in the order thermococcales, ''T. litoralis'' is an irregular hyperthermophile

coccus A coccus (plural cocci) is any bacterium or archaeon that has a spherical, ovoid, or generally round shape. Bacteria are categorized based on their shapes into three classes: cocci (spherical-shaped), bacillus (rod-shaped) and spiral ( of whi ...

that grows between . Unlike many other thermococci, ''T. litoralis'' is

non-motile Sessility is the biological property of an organism describing its lack of a means of self-locomotion. Sessile organisms for which natural ''motility'' is absent are normally immobile. This is distinct from the botanical concept of sessility, ...

. Its cell wall consists only of a single S-layer that does not form hexagonal lattices. Additionally, while many thermococcales obligately use sulfur as an electron acceptor in metabolism, ''T. litoralis'' only needs sulfur to help stimulate growth, and can live without it. ''T. litoralis'' has recently been popularized by the scientific community for its ability to produce an alternative DNA polymerase to the commonly used

Taq polymerase ''Taq'' polymerase is a thermostable DNA polymerase I named after the thermophilic eubacterial microorganism ''Thermus aquaticus,'' from which it was originally isolated by Chien et al. in 1976. Its name is often abbreviated to ''Taq'' or ''Ta ...

. The ''T. litoralis'' polymerase, dubbed the vent polymerase, has been shown to have a lower error rate than Taq but due to its

proofreading Proofreading is the reading of a galley proof or an electronic copy of a publication to find and correct reproduction errors of text or art. Proofreading is the final step in the editorial cycle before publication. Professional Traditional ...

3’–5’

exonuclease Exonucleases are enzymes that work by cleaving nucleotides one at a time from the end (exo) of a polynucleotide chain. A hydrolyzing reaction that breaks phosphodiester bonds at either the 3′ or the 5′ end occurs. Its close relative is the ...

abilities.

DNA polymerase

The

DNA polymerase A DNA polymerase is a member of a family of enzymes that catalyze the synthesis of DNA molecules from nucleoside triphosphates, the molecular precursors of DNA. These enzymes are essential for DNA replication and usually work in groups to create ...

of ''Thermococcus litoralis'' is stable at high temperatures, with a

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

of eight hours at and two hours at . It also has a proofreading activity that is able to reduce mutation frequencies to a level 2–4 times lower than most non-proofreading DNA polymerases.

Habitat and ecology

''T. litoralis'' grows near shallow and deep sea hydrothermal vents in extremely hot water. The optimal growth temperature for ''T. litoralis'' is 85–88 °C. It also prefers slightly acidic waters, growing between pH 4.0 to 8.0 with the optimal pH between 6.0–6.4. Unlike many other hyperthermophiles, ''T. litoralis'' is only facultatively dependent on sulfur as a final electron acceptor in fermentation, producing hydrogen gas in its absence and hydrogen sulfide when present. Additionally, ''T. litoralis'' has been shown to produce an exopolysaccharide (EPS) that could possibly help it form a

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...

. It is made of

mannose Mannose is a sugar monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylation ...

sulfites Sulfites or sulphites are compounds that contain the sulfite ion (or the sulfate(IV) ion, from its correct systematic name), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are widel ...

, and phosphorus.

Physiology

''T. litoralis'' can utilize

pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic aci ...

maltose } Maltose ( or ), also known as maltobiose or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) bond. In the isomer isomaltose, the two glucose molecules are joined with an α(1→6) bond. Maltose is the two- ...

, and

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

as energy sources. In a laboratory setting, ''T. litoralis'' must be supplied with amino acids in order to grow at non-reduced rates. The only amino acids it does not require are

asparagine Asparagine (symbol Asn or N) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the depro ...

, glutamine, alanine, and

glutamate Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can syn ...

. These amino acids may not be vital for ''T. litoralis'' because asparagine and glutamine tend to

deaminate Deamination is the removal of an amino group from a molecule. Enzymes that catalyse this reaction are called deaminases. In the human body, deamination takes place primarily in the liver, however it can also occur in the kidney. In situations of e ...

at high temperatures found around hydrothermic vents and alanine and glutamate can usually be produced by other hyperthermophilic archaea. The main carbon source for ''T. litoralis'' seems to be maltose, which can be brought into the cell via a maltose- trehalose ABC transporter. ''T. litoralis'' has a specialized glycolytic pathway called the modified Embden–Meyerhoff (EM) pathway. One way the modified EM pathway in ''T. litoralis'' deviates from the common EM pathway is that the modified version contains an ADP dependent hexose kinase and

PFK Phosphofructokinase (PFK) is a kinase enzyme that phosphorylation, phosphorylates fructose 6-phosphate in glycolysis. Function The enzyme-catalysed transfer of a phosphoryl group from Adenosine triphosphate, ATP is an important reaction in a ...

instead of an ATP dependent versions of the enzymes.

Novel strains

New DNA analysis has shown several isolates of ''T. litoralis'', MW and Z-1614, which are most likely new strains. MW and Z-1614 were confirmed to be strains of ''T. litoralis'' through DNA-DNA hybridization, C–G ratios (38–41 mol%), and immunoblotting analyses. They slightly differ in morphology from the previously isolated ''T. litoralis'' in that they all have flagella. Through the same processes it has been shown that the previously discovered ''Caldococcus litoralis'' was actually ''T. litoralis''. The genome for ''T. litoralis'' has yet to be fully sequenced.

References

External links