Methanococcus jannaschii
A Microbial Biorealm page on the genus Methanococcus jannaschii
Classification
Higher order taxa
- Superkingdom: Archaea
- Phylum: Euryarchaeota
- Class: Methanococci
- Order: Methanococcales
- Family: Methanocaldococcaceae
- Genus: Methanocaldococcus (syn: Methanococcus)
Species
Genus species - Methanocaldococcus jannaschii
- synonym: Methanococcus jannaschii
Description and significance
Methanococcus jannaschii is an autotropic hyperthermophillic organism that belongs to the kingdom of Archaea. They were found to live in extreme environments such as hypothermal vents at the bottom of the oceans in which water reaches boiling temperature or pressure is extremely high (Bult, C.J. et. al., 1996). The evolutionary of these organisms and the biological mechanisms that they use to not only survive but also thrive in such extreme environments are of great interest to current researches.
In 1982, M. jannaschii was first isolated in the East Pacific Rise, near the western coast of Mexico. The organism was found from a sample sediment taken from a 2600 m deep “white smoker” chimney. Its extreme habitat of temperature between 48oC-94oC, pressure at 200atm, a pH of 5.2-7, and 1.0-5.0% NaCl leads experts to a conclusion that these organisms must have modified and unique adaptations for optimal growth at high temperature, high pressure, and also moderate salinity level (Tsoka et. al, 2003). Moreover, cellular structure of M. jannaschii revealed that they are irregular cocci (have irregular spherical shape). Their motility is by utilizing polar bundles of flagella (Tsoka et. al., 2003). Characteristic to any organism that belongs to the kingdom Archaea, M. jannaschii lacks cell wall; however, they do possess cell envelope that is made up of cytoplasmic membrane and a protein surface layer (S-layer) (Sleytr et. al., 2007).
Methanococcus jannaschii belongs to a specific group called methanogens, or methane producers (Tumbula and Whitman, 1999). Methanogens are physiologically specialized to undergo fueling reactions to produce methane as the end product (Reeve, 1992). They are ultimately autotropic single-celled organisms. Being an autotropic organism, M. jannaschii is strictly anaerobic and uses only carbon dioxide as its sole carbon source. Its main pathway for energy production is through methanogenesis, a process during which hydrogen is used as an energy source to reduce carbon dioxide to methane (Zhu et. al., 2004). Methanogens are extremely important to anaerobic environments because they convert organic compounds into methane, which then rises into the aerobic environment. By doing so, these organisms provide a pathway for compounds that exist in anaerobic environment to escape into the atmosphere, where it acts as a natural gas resource (Reeve, 1992).
M. jannaschii became the first organism in the archaea to have its complete genome sequenced (Bult, C. J. et. al, 1996). Its genomic structure, along with the unique lifestyle, has gradually provided insights into understanding the organism’s adaptations to its extreme habitat. More importantly, the knowledge gained from studying the metabolic processes, the enzymes, and the proteins that are specifically involved in these processes will lead to deeper understanding of the evolution of Archaea. In studying the interaction between M. jannaschii and its environment, many evolution questions about our environments could potentially be answered.
Genome structure
Methanococcus jannaschii was the first organism of the kingdom Archaea to be completely sequenced in 1995 (Bult, C.J. et. al., 1996). Three characteristic elements that make up the genome of M. jannaschii are: a large circular chromosome, a large-circular extra chromosome, and a small circular extra-chromosome (Bult, C.J. et. al., 1996). Using whole-genome random sequencing, it was found that:
1. The large circular chromosome has a length of 1.66 mega base pair. Within the chromosome, there are a total of 1729 protein-coding regions, and the percentage of G+C content is 31.4%.
2. The large circular extra-chromosome has a length of 58 kilo base pair. The total protein-coding regions are 45, and the percentage of G+C content is reported as 28.2%.
3. The small circular extra-chromosome contains 16.5 kilo base pair. The predicted protein-coding regions are 12, and the G+C content percent is 28.9%.
The genome structure of Methanococcus jannaschii finally provided solid support for the hypothesis that Archaea is indeed a separate domain of life from Bacteria and Eukarya, and that Archaea is more closely related to Eukarya. This hypothesis was made several years before genome sequencing even existed (Tsoka et. al., 2003). Although the M. jannaschii genome is quite small compared to the genome of well-known species such as Eschericia coli (only 40% of E. coli genome), researchers believe that the genome is very specific to the autotropic lifestyle of the organism (Zhu et. al., 2004). Until now, only about 52% of the proteins in the genome have been identified and assigned to functions (Zhu et. al., 2004). However, their hyperthermophillic properties and their special mechanisms to their extreme environments leads to conclusion that these proteins are strictly involved in energy production, specifically methanogenesis, cell division, metabolism, and also maintaining the organism’s lifestyle (Zhu et. al., 2004).
Cell structure and metabolism
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Ecology
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Application to Biotechnology
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Current Research
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References
Edited by Tina Nguyen Tran of Rachel Larsen and Kit Pogliano
