Thermococcus celer

Thermococcus celer is a Gram-negative, spherical-shaped archaeon of the genus Thermococcus. The discovery of T. celer played an important role in rerooting the tree of life when T. celer was found to be more closely related to methanogenic Archaea than to other phenotypically similar thermophilic species. T. celer was the first archaeon discovered to house a circularized genome. Several type strains of T. celer have been identified: Vu13, ATCC 35543, and DSM 2476. T. celer was discovered by Dr. Wolfram Zillig in 1983. The organism was isolated on the beaches of Vulcano, Italy, from a sulfur-rich shallow volcanic crater. Original samples were isolated from the depths of the marine holes and inoculated into 10-ml anaerobic tubes. The tubes contained 100 mg of elemental sulfur and a solution of 95% N2 and 5% H2S. The pH was subsequently adjusted to a range of 5-6 through the addition of CaCO3. To ensure that no oxygen had permeated the sample, researchers used the oxygen indicator resazurin. Growth was achieved by enrichment with Brock’s Sulfolobus medium, which contains elemental sulfur and yeast, both of which are required by T. celer for optimal growth. Following enrichment, the samples were plated onto polyacrylamide gel and then incubated at 85°C in an anaerobic environment. Once colony growth had been observed, the cells were subjected to centrifugation prior to purification in a TA buffer solution (0.05 mol/l Tris HCl, 0.022 mol/l NH4Cl, 0.01 mol/l β-mercaptoethanol). Following Sanger sequencing of the 16s rRNA, both parsimony and distance matrix analyses were performed to determine the position of T. celer on the tree of life. T. celer was found to be more closely related to the methanogenic archaebacteria than the thermophilic archaebacteria. This discovery resulted in a rerooting of the archaebacterial tree and subsequently placed T. celer in a clade with the methanogens based upon their close phylogenetic relationship. This placement was further supported following analysis of the organizational genome structure of the both species’ rRNA genes. Both Thermococcus and methanogenic archaebacteria have a tRNA spacer gene located between the 16s rRNA gene and 23s This spacer gene is not found in any other thermophilic archaebacteria species. T. celer is related to Pyrococcus woesei, both belonging to the order Thermococcales. Both are strictly anaerobic and sulphur-reducing. T. celer also shares a close relationship with Thermococcus litoralis, both belonging to the same genus, but T. celer has shown to be much more Sulphur-dependent than T. littorals. T. celer is currently classified as a thermophilic Archaeon. Since the discovery of T. celer, the term archaebacteria has been replaced with Archaea as to reflect the most current phylogenetic relationships discovered between the organisms. Thermococcus is constructed from two Greek nouns: therme (Greek, meaning heat), and kokkos (Greek, meaning grain or seed). Celer is derived from the Greek, meaning fast, in reference to the species' high growth rates. T. celer is a Gram-negative, spherical organism around 1 μm diameter. Observation using electron microscopy revealed that T. celer uses a monopolar polytrichous flagellum for movement. During replication, T. celer is condensed to a diploform shape as seen by phase contrast microscopy. The T. celer plasma membrane possesses large amounts of glycerol diether lipids compared to relatively small amounts of diglycerol tetraether lipids. Within glycerol diether lipids, phytanyl (C20) is the hydrocarbon component, and within diglycerol tetraether lipids, biphytanyl (C40) is the hydrocarbon component. The cell wall, or S-layer, of T. celer functions as protection from cell lysis as a result of changes in osmotic gradients. The envelope S-layer consists of glycoprotein subunits arranged into a two-dimensional paracrystalline hexagonal structure. The T. celer cell envelope lacks muramic acid, indicating resistance to penicillin and vancomycin.