Methanogens (methane-producing microbes)belong to the domain Archaea, and 16S rRNAgene sequences indicate that they form a phylogeneticallydistinct clade within the kingdomEuryarchaeota. The order Methanosarcinales isone of the five orders of methanogens. Thesemicrobes catalyze the terminal step in the degradationof organic matter in anoxic environmentswhere light and terminal electron-acceptorsother than CO2 are limiting. Representatives ofthe Methanosarcinales are widespread and cosmopolitanin anaerobic environments. They arefound in freshwater, marine environments, andextremely halophilic sediments as well as inanaerobic sludge digestors and the gastrointestinaltracts of animals. Use of molecular techniqueshas also identified Methanosarcinales inthe deep terrestrial subsurface environmentssuch as in the gold mines in South Africa.Members of the order Methanosarcinales arecoccoids, pseudosarcinae, or sheathed rods. Mostcells have a protein cell wall, and some are surroundedby a sheath or acidic heteropolysaccharide;no peptidoglycan or pseudomurein ispresent. Hydroxyarchaeol is usually present inthe lipids, which contain myo-inositol, ethanolamineand glycerol as polar headgroups. Cells arevery strictly anaerobic and obtain energy withthe concomitant production of methane. Methanosarcinaleshave the widest substrate range ofmethanogens: many can grow by reducing CO2with H2, by dismutating methyl compounds, orbởi sự chia tách của axetat. Một số loài có thể sử dụngchỉ có một trong những chương trình catabolic, nhưng những người kháccó thể sử dụng tất cả ba.Bộ Methanosarcinales này bao gồm haigia đình có, Methanosarcinaceae và Methanosaetaceae.Một số đặc điểm đặc biệt của họđược liệt kê trong bảng 1.
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