Thermococcus kodakarensis

A Microbial Biorealm page on the genus Thermococcus kodakarensis

Thermococcus kodakaraensis Image by F. Fukuri, Kyoto University

Classification

Higher order taxa

cellular organisms; Archaea; Euryarchaeota; Thermococci; Thermococcales; Thermococcaceae; Thermococcus

Genus

Thermococcus kodakarensis

NCBI: Taxonomy

Description and significance

Previously characterized as Pyrococcus sp., Thermococcus kodakarensis is a sulfur-reducing hyperthermophilic archaeon which typically inhabits marine hydrothermal vents and terrestrial hot sulfur springs. This organism and other hyperthermophiles are of great interest as they have evolved mechanisms for adaptation to extremely high temperature enviorenments. The prokaryote grows at an optimal temperature of 86C, between the ranges of 60-100C, and in a pH range of 5-9. Although this organism is a representation of simple life forms, it grows and thrives in temperatures up to the boiling point of water.(T. Imanaka et al) In the absence of sulfur, these heterotrophs ferment a variety of organic compounds, including amino acids, peptides, and sugars. Recent accumulation of 16sRNA sequences has indicated the organism belongs to the Thermococcus genus, and not to the originally hypothesized Pyrococcus genus.

Thermococcus kodakarensis was isolated from a solfatara (a volcanic area that releases only hot vapors and sulfurous gases into the environment) on Kodakara Island, Japan, and sequenced by the Kyoto University, Japan.(Morikawa M. et al) This organism produces commercially applicable thermostable DNA polymerases and enzymes that would be useful for such techniques as PCR (Polymerase Chain Reaction).

Thermococcus kodakarensis belongs to the most commonly isolated hyperthermophilic organisms, Thermococcus sp. and are often isolated from marine hydrothermal vents and terrestrial hot sulfur springs. The genome of T. kodakarensis encodes several proteins found within genetic elements similar to those in Pyrococcus spp., implying mechanisms of horizontal gene transfer of mobile elements among the order Thermococcales.

Hyperthermophiles are microorganisms that can grow and survive above 60 C and at an optimum temperature of 80 C. Thermococcus belongs to a group of hyperthermophiles that can grow at extremely high temperature including 100 C (the boiling point of water). (Prieur D. et al) These microorganisms were discovered in 1982 by Stetter and are considered to be the most ancient forms of life. (Adams MW et al) Most hyperthermophiles depend entirely on the reduction of elemental sulfur to hydrogen sulfur for significant growth, resulting in the hindrance of large-scale culture in conventional fermentation systems. (Lepage E et al) After Stetter's first isolation of hyperthermophiles, there have been approximately 20 different genera discovered and added to the class of microorganisms.

Genome structure

The Thermococcus kodakaraensis genome contains 2.09 Million base pairs (bp) and is predicted to have approximately 2357 genes. The average size of a microbial genome is known to be approxiamately 4 Mb, twice the size of Thermococcus kodakaraensis. The chromosome has a circular topology and the GC content is estimated to be 38 mol%. Seven genes for probable transposases and four virus-related regions are found within the genome. (Fukui. T et al)

Cell structure and metabolism

Thermococcus kodakarensis has an irregular cocci (1-2 µm diameter) cell structure and is motile with several polar flagella. T. kodakarensis has a single ether lipid membrane. This strictly anaerobic (existing without oxygen) and sulfur reducing organism uses amino acids, peptides, pyruvate, and starch as its carbon and energy sources. Metabolic pathways of T. kodakarensis include gluconeogenesis and glycolysis and the products of metabolism are hydrogen and hydrogen sulfide gas. (Fukui. T et al)

Ecology

Thermococcus thrive in deep sea hydrothermal vents. The microorganism plays an important role in the ecology of hot-water ecosystems due to the ubiquitous characterisitics exhibited in their habitat. In addition, Thermococcus is the most commonly isolated hyperthermophile, suggesting great abundance throughout the microbial community. Fukui F.

Application to Biotechnology

Thermococcus kodakarensis attractiveness stems from its ability to survive and grow in extreme environments. The organism's mechanisms of adaptation to such environments has peaked several interests within the biological community. Special proteins of Thermococcus kodakarensis enable it to exhibit some of the specific traits of the genus Thermococcus including additional pyruvate oxidation, nucleotide metabolism, metal ion transporters, improved stress response system, and a distinct restriction system. Fukui et al In addition, Thermococcus kodakarensis produces at least three extracellular proteases which exhibit maximum activity at a pH of 7.0 and a temperature of 110 degrees. Further experiments proved these proteases to be thermostable thiol proteases. M. Morikawa All enzymes of Thermococcus kodakarensis are found to exhibit remarkable thermostability and are potential resources for procedures such as PCR where enzymes are required to be stable at relatively high temperatures.

Current Research

Hyperthermophilic organisms have become widely studied model microorganisms in many fields. Different fields of study focus on their adaptation to extreme temperatures, phylogeny and genome evolution, molecular deciphering of DNA replication mechanisms in Archaea, and valuable sources of biotenoligically important products (Prieur D.)