# Methanococcaceae
**Methanococcaceae** is a family of anaerobic archaea in the order Methanococcales: coccoid methanogens that are motile by means of flagella and produce methane by using carbon dioxide as an electron acceptor.[1](https://www.ncbi.nlm.nih.gov/mesh/68017016) The family, validly named by Balch and Wolfe in 1981, contains the genera *Methanococcus* and *Methanothermococcus* and is one of the best-studied groups of hydrogenotrophic methanogens.[2](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2183&mode=Info) • [3](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/methanococcales)
| Key fact | Detail |
|---|---|
| Rank and authority | Family Methanococcaceae Balch and Wolfe 1981; NCBI taxonomy ID 2183[2](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2183&mode=Info) |
| Placement | Archaea; Methanobacteriota; Methanomada group; Methanococci; Methanococcales[2](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2183&mode=Info) |
| Physiology | Strictly anaerobic methanogens, motile by flagella, using CO2 as an electron acceptor[1](https://www.ncbi.nlm.nih.gov/mesh/68017016) |
| Genera | *Methanococcus* (mesophilic) and *Methanothermococcus* (moderately thermophilic)[3](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/methanococcales) |
| Growth temperatures | *Methanococcus maripaludis* strains grow optimally at 37 °C; *Methanothermococcus okinawensis* at 62 °C and *M. thermolithotrophicus* at 65 °C[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC8097290/) |
| Sequence identity | Mean 16S rRNA similarity within the family is 93.4%; mean mcrA (methyl-coenzyme M reductase gene) similarity is 83.2%[5](https://journals.asm.org/doi/10.1128/aem.00553-08) |
| Nomenclature status | Listed as a correct name by LPSN (last update February 2025) and recovered as f__Methanococcaceae in the Genome Taxonomy Database[6](https://onlinelibrary.wiley.com/doi/10.1002/9781118960608.fbm00100.pub2) |
## Taxonomy and classification
The family sits within the order Methanococcales in the class Methanococci, part of the phylum Methanobacteriota (Methanomada group) in the NCBI taxonomy.[2](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2183&mode=Info) The name was introduced in the 1979 reevaluation of the methanogens by Balch, Fox, Magrum, Woese, and Wolfe, and validated in 1981.[2](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2183&mode=Info) In the Genome Taxonomy Database the family appears as d__Archaea / p__Methanobacteriota_A / c__Methanococci / o__Methanococcales / f__Methanococcaceae.[6](https://onlinelibrary.wiley.com/doi/10.1002/9781118960608.fbm00100.pub2)
The scope of the order has changed since the family was named. Older references described Methanococcales as comprising a single family, Methanococcaceae, with the single genus *Methanococcus*.[7](https://www.ncbi.nlm.nih.gov/mesh/68017015) A second family, Methanocaldococcaceae, holding the extremely thermophilic genera *Methanocaldococcus* and *Methanotorris*, is now recognized alongside Methanococcaceae, whose genera are the mesophilic *Methanococcus* and the moderately thermophilic *Methanothermococcus*.[3](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/methanococcales) • [8](https://cibnor.repositorioinstitucional.mx/jspui/bitstream/1001/81/1/garcia_j.pdf)
## Physiology and metabolism
Members are strict anaerobes that gain energy from hydrogenotrophic methanogenesis, the reduction of CO2 with H2 to methane. This pathway binds C1 species to the carriers methanofuran, tetrahydromethanopterin, and coenzyme M at different oxidation states; the four reduction steps involve one molybdopterin-based two-electron reduction, two coenzyme F420-based hydride transfers, and one coenzyme F430-based radical process, with a sodium-ion-linked methyl transfer and flavin-based electron bifurcation driving the energetically demanding steps.[9](https://www.annualreviews.org/doi/10.1146/annurev-micro-011720-122807) The pathway is barely exergonic, conserving just enough energy for a modest metabolism, which is why the enzyme machineries carry unusual metal-containing cofactors.[9](https://www.annualreviews.org/doi/10.1146/annurev-micro-011720-122807)
The mcrA gene, encoding a subunit of methyl-coenzyme M reductase, the key enzyme of methane formation, is a standard phylogenetic marker for this group; within Methanococcaceae its sequences average 83.2% similarity, against 93.4% for 16S rRNA.[5](https://journals.asm.org/doi/10.1128/aem.00553-08)
## Genera and temperature range
The two genera differ mainly in growth temperature. *Methanococcus* species are mesophiles: *M. maripaludis* strains grow optimally at about 37 °C, *M. voltae* at 37 °C, *M. vannielii* at 35 °C, and *M. aeolicus* at 46 °C.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC8097290/) *Methanothermococcus* species are moderate thermophiles: *M. okinawensis* grows optimally at 62 °C and *M. thermolithotrophicus* at 65 °C.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC8097290/) The wide distribution of extreme thermophily among related Methanococcales suggests that the mesophilic *Methanococcus* may have evolved from thermophilic ancestors.[3](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/methanococcales)
## Phylogeny and open taxonomic boundaries
Molecular trees recover the family as monophyletic, but the boundary between its two genera is unsettled. A phylogeny of the malate dehydrogenase (MalDH) protein across Methanococcales recovers the monophyly of the families Methanocaldococcaceae and Methanococcaceae and of the genera *Methanocaldococcus* and *Methanotorris*, while *Methanothermococcus* and *Methanococcus* species are mixed in the tree, a recurring observation across studies that has been argued to require redefinition of the two genera.[10](https://pmc.ncbi.nlm.nih.gov/articles/PMC11631191/) Within the wider methanogen radiation, Methanococcales belongs to the so-called Class I methanogens together with Methanobacteriales and Methanopyrales, a grouping whose monophyly has received only weak statistical support in protein-concatenation analyses.[11](https://pmc.ncbi.nlm.nih.gov/articles/PMC2699033/)
## References
1. [Methanococcaceae, MeSH, NCBI](https://www.ncbi.nlm.nih.gov/mesh/68017016)
2. [Taxonomy Browser: Methanococcaceae, NCBI](https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2183&mode=Info)
3. [Methanococcales: an overview, ScienceDirect Topics](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/methanococcales)
4. [The Molecular Determinants of Thermoadaptation: Methanococcales as a Case Study, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC8097290/)
5. [Phylogenetic Comparison of the Methanogenic Communities from an Acidic, Oligotrophic Fen and an Anaerobic Digester, Applied and Environmental Microbiology](https://journals.asm.org/doi/10.1128/aem.00553-08)
6. [Methanococcaceae, Rother, in Bergey's Manual of Systematics of Archaea and Bacteria, Wiley](https://onlinelibrary.wiley.com/doi/10.1002/9781118960608.fbm00100.pub2)
7. [Methanococcales, MeSH, NCBI](https://www.ncbi.nlm.nih.gov/mesh/68017015)
8. [Órdenes, familias y géneros de arqueas metanógenas (16S rRNA), CIBNOR repository](https://cibnor.repositorioinstitucional.mx/jspui/bitstream/1001/81/1/garcia_j.pdf)
9. [Shima, Huang, Wagner, Ermler (2020). Structural Basis of Hydrogenotrophic Methanogenesis. Annual Review of Microbiology 74:713-733](https://www.annualreviews.org/doi/10.1146/annurev-micro-011720-122807)
10. [The Characterization of Ancient Methanococcales Malate Dehydrogenases, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11631191/)
11. [Gene Order Phylogeny and the Evolution of Methanogens, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC2699033/)
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*Topic: Encyclopedia › Life and health › Microorganisms and fungi › Archaea › Archaeal taxonomy and diversity › Euryarchaeota › Methanogenic euryarchaeal orders › Methanobacteriales and Methanococcales taxa › Methanococcaceae*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Sep 30, 2026; Oct 11, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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