Methanosarcinales
The order Methanosarcinales is composed of two families, Methanosarcinaceae and Methanosaetaceae, which are distinguished by 16S rRNA sequence similarities below 88% and differences in substrates for methanogenesis, lipid components, and cell wall structu
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K. N. Timmis (ed.), Handbook of Hydrocarbon and Lipid Microbiology, DOI 10.1007/978-3-540-77587-4_46, # Springer-Verlag Berlin Heidelberg, 2010
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Methanosarcinales
Abstract: The order Methanosarcinales is composed of two families, Methanosarcinaceae and Methanosaetaceae, which are distinguished by 16S rRNA sequence similarities below 88% and differences in substrates for methanogenesis, lipid components, and cell wall structures. The Methanosarcinaceae are all capable of producing methane from methyl group containing compounds, and some can use acetate or H2/CO2. The cells can form aggregates within an outer layer composed of heteropolysaccharide. The Methanosaetaceae can only produce methane by splitting acetate. The cells can form chains within a proteinaceous sheath.
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Introduction
Members of the order Methanosarcinales have the widest substrate range among methanogens. All members can produce methane by disproportionating methyl-group containing compounds (methanol, methylamines, or methyl sulfides) or by splitting acetate. Some mesophilic Methanosarcia species can reduce CO2 with H2, but formate, secondary alcohols, and ethanol are not used as electron donors. Ammonium and sulfide serve as the major nitrogen and sulfur sources, respectively. Their cellular morphologies are diverse, including cocci, pseudosarcinae, and sheathed rods. Most cells have protein cell walls, and some cells are surrounded by a sheath or acidic heteropolysaccharide. Most strains are nonmotile. The cellular lipids contain archaeol, hydroxyarchaeol, and caldarchaeol. Polar lipids can contain glucose, galactose, mannose, myo-inositol, ethanolamine, serine, and glycerol, depending upon the species. Most species of Methanosarcinales are mesophilic. Four species are moderately thermophilic (Methanosarcina thermophila, Methanomethylovorans thermophila, Methanosaeta thermophila, and Methermicoccus shengliensis), and four species are psychrotolerant (Methanococcoides alaskense, Methanococcoides burtonii, Methanosarcina lacustris, and Methanosarcina baltica). Most species grow best at near neutral pH, except for three species that are alkaliphilic (Methanolobus oregonensis, Methanolobus taylorii, and Methanosalsum zhilinae). Many species were isolated from marine environments and require a salinity near that of seawater for optimal growth. Some species are halophilic or halotolerant.
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Descriptive Features
Descriptive properties of members of the Methanosarcinales are summarized in > Table 1. Further information can be found in (Boone et al., 2001; Kendall and Boone, 2006).
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Taxonomy and Phylogeny
The order Methanosarcinales is divided into two families, Methanosarcinaceae and Methanosaetaceae, based on phenotypic properties and 16S rRNA gene sequence analysis (> Fig. 1). All members of the family Methanosarcinaceae are coccoid, pseudosarcinae, or ‘‘cysts’’ and are able to grow with methyl-group containing compounds. They may also produce methane by splitting acetate. The family Methanosaetaceae is represented by only one gen
