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1. IDENTIFYING CHARACTERISTICS
The above picture shows Thermococcus under phase contrast microscopy (100X).
As seen in the figure to the left, the thermococci have retained that phenotype from the common ancestry of Euryarchea & Crenarchaea, which shares characteristics closely with Archaeoglobus, and Thermoplasma. The Methanogens are also a part of the family Archaebacteria.
Archaebacteria are distinguished by cell walls with pseudopeptidoglycan or protein components, and cell membranes composed of branched hydrocarbons linked to glycerol molecules. T.celer is the most primative organism known, i.e. it is closer to the 'root' of the universal tree than any other known living organism.
Taxonomically the Archaea are divided into two kingdoms, euryarchaeota and crenarchaeota, and five subgroups, extreme halophiles, methanogens, extreme thermophiles, thermoacidophiles, and strickly anaerobic crenarchaeotes. In general, the archaea are tolerant of extremely harsh environments. Cell membranes of archaea are unique. Their branch-chained, ether-linked lipids differ greatly from those of all other life forms. The basic structure is a 5-C isoprene unit. These are linked to form chains of up to 20 C; two such chains may link to form a 40-C chain. Chains are ether linked to glycerol, not ester linked, as in bacteria and eucarya. Thermophilic archaea, the tetraether membrane is predominant.
Thermococcus is remarkable because it is able to maintain chromosomal integrity at temperatures up to 103 C with very little accumulation of DNA breaks. It also is highly resistant to radiation and can withstand doses up to 1.5 kGy. These characteristics suggest there is a highly effective DNA repair systems in hyperthermophiles. These organisms also possess an array of highly thermostable enzymes that could prove to be important biocatalysts. Comparison of the DNA sequence of this organism with others may provide insight into these unique characteristics.
These organisms grow by anaerobic sulfur respiration
S + organics ---> H2S + CO2
A sodium chloride concentration of 0.5-5% is required for growth. The optimal sodium chloride concentration is less than that of seawater, probably reflecting the fact that it grows in sediments near 100 C where the salt concentration is less than that of seawater. Elemental sulfur stimulates growth by removing the waste product, hydrogen. It can utilize peptides, proteins and some carbohydrates (e.g., starch and maltose) as carbon sources.
Because Thermophiles survive in the highest temperature of any living organism, it has been hypothesized that they have this ability due to abnormal changes in their proteins' structure. This change in structure keeps the protein from denaturing in the hot temperatures. Presently, experimental data has not shown as large a difference in the proteins as expected. However, theories of a protein that allows the organism to adapt have been tested for. A heat-shock protein has been found in the thermophile Sulfolobus shibatae (negative of flagella stain right). This Protein works as a molecular cahperone, which aids in protein folding. This folding is essential in the formation of new proteins. Production of which is accelerated when the cell is stressed. These proteins replace the proteins that are denatured due to the stress.
3. ISOLATION AND ECOLOGY
T. littoralis is the source of vent DNA polymerase, used extensively in PCR. When scientists at New England Biolabs cloned the gene for the enzyme, they were surprized to find that it contains an extra sequence of non-DNA-polyermase. They assumed it was an intron, but found that the mRNA isn't spliced and the extra sequence is translated into a novel domain in the enzyme. This polypeptide domain is a peptidyltransferase that specifically splices itself out of the DNA polymerase, rejoining the 2 parts of the DNA polymerase as it leaves. This protein-splicing reaction is remarkably analogous to RNA-splicing by introns, and so it's called an 'intein' (intervening protein).Once the intein has removed itself from the DNA polymerase, it has another activity - in is a transposase. This enzyme cleaves DNA specifically at the ends of the intein-encoding sequence and directs a DNA repair process that results in the insertion of the intein into other protein-encoding genes - in other words, the intein is also a transposon.
Thermococci, like their close relatives Pyrococci, are common in hot marine sediments and marine sand surrounding surfurous volcanoes. Thermococci are found especially in deep-sea hydrothermal vent areas. They are motile, via a distinctive tuft of 50 polar flagella at one end and are often found in pairs. The generation time is among the shortest found among the Archaea, only 37 minutes under optimal conditions.
An extremely thermophilic archaeon, strain AL662T, was isolated from a deep-sea hydrothermal vent located on the East Pacific Rise at a latitude of 21oN. This strain is a strictly anaerobic coccus, and its cells range from 0.8 to 2 um in diameter.
The optimum temperature, pH, and Sea Salt concentration for growth are 85oC, 6, and 20 to 40 g/liter, respectively. Strain AL662T grows preferentially on proteolysis products, on a mixture of 20 amino acids, and on maltose in the presence of elemental sulfur. The membrane lipids consist of di- and tetraether glycerol lipids. The DNA G+C content is 58 mol%. Sequencing of the 16S rRNA gene showed that strain AL662T belongs to the genus Thermococcus. On the basis of hybridization results, it is proposed that this strain should be placed in a new species, Thermococcus hydrothermalis.
4. ADDITIONAL SOURCES OF INFORMATION
Brock, Thomas D. 1986. Thermophiles: General, Molecular, and Applied Microbiology. Wiley Press. New York, N.Y. 50-55 pp.
Holt, J.G., N.R. Krieg, P.H.A. Sneath, J.T. Staley, and S.T. Williams. 1994. Bergey's Manual of Determinative Bacteriology. Ninth Edition. Williams and Wilkins. Baltimore, Maryland. 787 pp.
Noll, K. M. 1992. Archaebacteria (Archaea) and Applied Biochemistry. Cambridge University Press, London/New York. 87-92 pp.
Paul, E.A and F.E. Clark. 1996. Soil Microbiology and Biochemistry. 2nd Edition. Academic Press,Inc. San Diego, California. 84-85 pp.
5. LINKS TO OTHER SITES ON THERMOCOCCUS
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