# Methanosarcinales

Methanosarcinales is an order of Archaea in the class Methanomicrobia, phylum Methanobacteriota. The order Methanosarcinales contains both methanogenic and methanotrophic lineages, although the latter have so far no pure culture representatives. Methanotrophic lineages of the order Methanosarcinales were initially abbreviated as ANME (anaerobic methanotrophs) to distinguich from aerobic methanotrophic bacteria. Currently, those lineages receive their own names such as Ca. Methanoperedens, Ca. Methanocomedens (ANME-2a), Ca.Methanomarinus (ANME-2b), Ca. Methanogaster (ANME-2c), Ca. Methanovorans (ANME-3). The order contains archaeon with one of the largest genome, Methanosarcina acetivorans C2A, genome size 5,75 Mbp.
The organisms placed within the order can be found in freshwater, saltwater, salt-rich sediments, anaerobic digestors, and animal digestive systems. The order consist of mesophiles or moderately thermophillic, neutrophilic or alkaliphilic species with some able to grow at high salt concentrations (genera Methanohalobium , Methanohalophilus , and Methanosalsum). Most of the species in the order were isolated or detected in marine and freshawater sediments, soil with only a few specialized lineages adapted to the digestive tract of animals - genera Methanimicrococcus, Methanolapillus, and Ca. Methanofrustulum that can be found in termites/cockroaches, millipedes, and ruminants, respectively.
Most cells have cell walls that lack peptidoglycan and pseudomurein with notable presence of methanochondroitin in Methanosarcina genus. As all other methanogens, Methanosarcinales representatives are strictly anaerobic and utilize methanogenesis pathway as the only path for ATP production. However, besides common among other methanogens substrates H$_2$/CO$_2$, Methanosarcinales characterized by the ability to utilize acetate (aceticlastic methanogenesis), methylated compounds such as methanol or methnylamines (methylotrophic methanogenesis), or even methoxyalted aromatic compounds (methoxydotrophic methanogenesis).

## Phylogeny

| 16S rRNA based LTP_06_2022 | 53 marker proteins based GTDB 08-RS214 |
| Methermicoccaceae Methanosarcinales Methanosaetaceae [incl. Methanotrichaceae] Methanosarcinaceae | Methanosarcinales_A Methermicoccaceae Methanotrichales Methanotrichaceae [incl. Methanosaetaceae] Methanosarcinales "Methanocomedenaceae" (ANME-2a, ANME-2b) "Ethanoperedentaceae" (EX4572-44) "Methanoperedentaceae" (ANME-2d, AAA) "Methanogastraceae" (ANME-2c) Methanosarcinaceae |
The order Methanosarcinales contains the following families (genera comprising each family listed below corresponding family):

### Methanosarcinaceae Balch and Wolfe 1981

* Methanimicrococcus corrig. Sprenger et al. 2000
* Methanococcoides Sowers and Ferry 1985
* Methanohalobium Zhilina and Zavarzin 1988
* Methanohalophilus Paterek and Smith 1988
* Methanolobus König and Stetter 1983
* Methanomethylovorans Lomans et al. 2004
* Methanosalsum Boone and Baker 2002
* Methanosarcina Kluyver and van Niel 1936

### Methanotrichaceae Akinyemi et al. 2021

* Methanothrix Huser et al. 1983

### Methermicoccaceae Cheng et al. 2007

* Methermicoccus Cheng et al. 2007