A Microbial Biorealm page on the genus Methanococcus voltae
Higher order taxa
Genus species: Methanococcus voltae
Other Name: Methanococcus voltaei
Strains: Methanococcus voltae PS, Methanococcus voltae A3
Description and significance
Methanococcus voltae is a single-celled, gram-negative, coccoid-shaped organism that is a member of the domain Archaea (2) . It belongs to a specific group called methanogens, or methane producers (3). Archaea thrive under extreme environmental conditions. Methanogenic archaeobacterium occur in anaerobic environments, such as the intestinal tracts of animals, freshwater and marine sediments, and sewage. They are capable of producing methane from a limited number of substrates, including carbon dioxide and hydrogen, acetate, and methylamines: an important source of natural gas (4). M. voltae’s main pathway for energy production is through methanogenesis (5).
Archaea are similar to other prokaryotes in most aspects of cell structure but are unique with respect to the lipid composition of the cytoplasmic membrane and the structure of the cell surface (6). Most archaeal species have walls made of proteins or glycoproteins, which form the outermost envelope of the cell called the surface layer (S-layer), while other species’ membranes are composed of phospholipids (7, 6). The unique cell surface of archaea requires distinct solutions to the problem of how proteins cross this barrier to be either secreted into the medium or assembled as appendages at the cell surface (6).
Several genes for chromatin proteins are known in Archaea. Some include histones and histone-like proteins in Euryarchaeota, as well as a DNA binding protein, Alba, which was first detected in the crenarchaeote Sulfolobus solfataricus and is thought to be involved in transcriptional regulation (8). M. voltae harbors four genes coding for all these types of chromatin proteins (8).
M. voltae’s genomic structure and adaptations provide insight into understanding the organism’s interactions with its extreme habitat. “Methanococcus voltae (strain PS) is known to produce a filterable, DNase-resistant agent (called VTA, for voltae transfer agent), which carries very small fragments (4400 bp) of bacterial DNA and is able to transduce bacterial genes between derivatives of the strain” (9). M. voltae was found to have a system of gene transfer similar to general transduction except that the bacteriophage component (in terms of virus replication) is defective or absent (9). VTA is responsible for the transfer and its 4.4kb fragments of DNA are resistant to DNase.
Cell structure and metabolism
M. voltae is arranged in singles and pairs, is motile, aquatic, anaerobic, and has a mesophilic temperature range (1). Its head diameter is about 40nm, and tail length is about 61nm (10). It is a methanogen, has a carbon cycle, and is nonsporulating (16). M. voltae also has its DNA packaged at about 4.4kb, with a size of 2000kb (6, 7). M. voltae lacks a typical bacterial cell wall. Only a thin protein S-layer covers the plasma membrane (3, 10). The lack of a cell wall explains why Archaea are resistant to antibacterial antibiotics, which are often used as genetic markers (3). Its source of mobility is via utilization of its flagella. The flagella of M. voltae are predicted, from their gene sequences, to be about 22 to 25 kDa (2).
Archaea have lipids with links between the head group and side chains and makes the lipids more resistant to heat and acidity than bacterial and eukaryotic ester-linked lipids. The glycerol headgroup with two ether-linked side-chains is known as archaeol (9).
This species will produce methane by undergoing anaerobic metabolic processes. During methanogenesis, M. voltae undergoes a process during which hydrogen is used as an energy source to reduce carbon dioxide to methane. Hydrogen gas is used as an electron reductant (or electron donor) for carbon dioxide reduction into methane (5, 13).
Methanogens are extremely important to the anaerobic environments in which they live because they convert organic compounds into methane, which then rise into the aerobic environment. Through this process, these organisms provide a pathway for compounds that exist in anaerobic environments to escape into the atmosphere, thus acting as a natural gas resource (14).
M. voltae needs selenium for optimal growth and energy production (12). High concentrations of selenium are toxic for most organisms, and detoxification can be achieved by volatilization through methylation (12). Dimethylselenide is one product of methylation and has been monitored in soil and marine environments where M. voltae live (12).
Archaea may have a great ecological impact in the production of methane. As methane is a powerful greenhouse gas, archaea may be partly responsible for global warming, and with a greater understanding of these organisms may come better solutions to alternate fuels and renewable sources of energy.
M. voltae has not been identified as a pathogen (3, 16). There are no known diseases that are caused by this organism.
Application to Biotechnology
Energy production from M. voltae is of great interest in biotechnology (11). As mentioned previously, M. voltae undergoes methanogenesis which is an anaerobic pathway that converts bacterial organic products during fermentation or degradation to carbon dioxide and methane. Different methylation products have also been found, helping detoxify environments for other organisms living in close relation to M. voltae (12). The most abundant one is dimethylselenide (12).
The genome sequence M. voltae has still to be published. Researchers from the Joint Genome Institute and Molecular Dynamics are currently working on sequencing the genome (15, 16). Once the entire genome has been sequenced, it may be compared to others for further analysis.
Although the genome has not been sequenced, there is a lot of current research on this organism. As mentioned above, dimethylselenide is a selenium detoxification product found in various environments, including marine habitats, and is, therefore, available to M. voltae in nature (12). Because M. voltae thrives in a selenium rich environment, different possible strategies to evade selenium deprivation occurring in the habitat of M. voltae and other archaeon can be envisioned. “Current research is being done to test if the organism may provide genetic information for isoenzymes lacking selenium, which may replace or supplement essential selenoproteins upon selenium deprivation. Alternatively, the organism might attain the ability to obtain selenium from sources not amenable as long as the element is freely available in sufficient concentrations” (12).
Another area of current research studies protein synthesis, especially proteins that are involved in making up the cell envelope, or the S-layer. It has been discovered that glycoproteins forming the S-layers are the most common component in the cell envelope, making it the basic building blocks of surface layers in archaeal organisms (7).
Some research has also focused on flagellin biosynthesis. Studies have shown that flagellins in archaeal species are unrelated to that of bacterial species (3). Further studies will investigate the minimum amount of flagella needed for motility, as well as the assembly mechanism of flagella in Archaea (3).
Current research is also being explored to test the effectiveness of antibiotics. Although most bacterial antibiotics are ineffective in archaea (because of its unique cell wall), some exceptions have been exploited to develop better markers for archaeal genetics (15). Puromycin is a drug that has been effective in both bacteria and archaea (15). It has been shown to inhibit growth in M. voltae and other methanogens (15).
[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.
(1) "Methanococcus voltae". NCBI Taxonomy Browser. 27 August 2007. 
(2) Bayley, DP. & Jarrell (1999) Overexpression of Methanococcus voltae Flagellin Subunits in Escherichia coli and Pseudomonas aeruginosa: a Source of Archaeal Preflagellin. American Society for Microbiology, 181(14): 4146–4153. Link to Article
(3) Tumbula, D., and Whitman. W., “Genetics of Methanococcus: possibilities for functional genomics in Archaea.” Molecular Microbiology 1999. Volume 33: 1-7.
(4) "Methanococcus voltae" Dictionary Reference. 27 Aug 2007. Link to Website
(5) Zhu W, Reich CI, Olsen GJ, Giometti CS, Yates JR 3rd., J. Proteome Res. 2004. Volume 3: 538-548.
(6) Albers, SV. (2006). Protein secretion in the Archaea: multiple paths towards a unique cell surface. Nature reviews. Microbiology, 4(7), 537-547. Link to Article
(7) Sleytr, UB., Egelseer, E., Ilk, N., Pum, D., and Schuster, B., “S-Layers as a basic building block in a molecular construction kit.” 2007. Volume 274(2): 323-334.
(8) Heinicke, I. (2004). Mutational analysis of genes encoding chromatin proteins in the archaeon Methanococcus voltae indicates their involvement in the regulation of gene expression. Molecular genetics and genomics, 272(1), 76-87. Link to Article
(9) Ng, SYM, & Ng. (2007). Archaeal signal peptidases. Microbiology, 153(2), 305-314. Link to Article
(10) Lang, AS, & LANG. (2007). Importance of widespread gene transfer agent genes in alpha-proteobacteria. Trends in Microbiology, 15(2), 54-62. Link to Article
(11) "Methanococcus voltae" 27 Aug 2007. Link to Website
(12) Niess, UM. (2004). Dimethylselenide demethylation is an adaptive response to selenium deprivation in the archaeon Methanococcus voltae. Journal of bacteriology, 186(11), 3640-3648. Link to Article
(13) Dawes, Edwin. Microbial Energetics. New York: Blackie. 1986
(14) Reeve, J.N. “Molecular biology of Methanogens.” Annu Rev Microbiol. 1992. Volume 46: 165–191.
(15) Allers, T. (2005). Archaeal genetics - The third way. Nature reviews. Genetics, 6(1), 58-73. Link to Article
(16) "Methanococcus voltae" Genamics GenomeSeek. 27 Aug 2007. Link to Website
Edited by Jeraldin Kuerbiss, student of Rachel Larsen
Edited by KLB