Keywords

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Taxonomy, Historical and Current

Methanosarcinaceae Balch and Wolfe 1981(Validation List no. 6, 1981; Effective Publication:Balch et al. 1979, 288)

Me.tha.no.sar.ci.na.ce’ae. N.L. fem. n. Methanosarcina, type genus of the family; suff. –aceae ending to denote a family; N.L. fem. pl. n. Methanosarcinaceae, the Methanosarcina family.

The members are generally irregular coccoid in shape, and the cells of some species form large aggregates. Cell division planes are not necessarily perpendicular. Cells possess a protein S-layer wall, and some species also produce an outer heteropolysaccharide layer. The lipids contain myo-inositol, ethanolamine, and glycerol as polar head groups. The family Methanosarcinaceae is the most versatile of all families of methanogenic Archaea with respect to the diversity of substrates used for energy generation: methylated amines and methanol are generally used, many species can grow on H2/CO2, some uses acetate, and other substrates used by some isolates are dimethyl sulfide, methanethiol, and even carbon monoxide. Formate is not used. Members of the Methanosarcinaceae have been found in a wide variety of anaerobic environments where methane is produced: freshwater, marine and hypersaline sediments, wetlands, thermal environments, oil wells, anaerobic waste treatment systems, and gastrointestinal tracts of animals. Some species are moderately thermophilic. Gas-vacuolated forms have been described (Boone et al. 2001a; Kendall and Boone 2006; Sowers et al. 1984b).

Type genus: Methanosarcina.

The mol% G+C of the DNA varies between 36 and 48.

The family Methanosarcinaceae was first proposed in 1979 (Balch et al. 1979), and the description was emended by Sowers et al. (1984). At the time of writing (January 2014), the family contained 9 genera with a total of 27 species, not including later subjective synonyms: Methanosarcina (11 species), Halomethanococcus (1 species (lost)), Methanimicrococcus (1 species), Methanococcoides (3 species), Methanohalobium (1 species), Methanohalophilus (3 species), Methanolobus (7 species), Methanomethylovorans (2 species), and Methanosalsum (1 species).

Different taxonomic rearrangements have been made within the family in the past:

  • The original type species of the genus Methanosarcina was Methanosarcina methanica Smit 1930 (Kluyver and van Niel 1936; Approved Lists, 1980). However, no organism fitting the description of M. methanica could be found. Following a Request for an Opinion (Mah and Kuhn 1984b), the Judicial Commission of the International Committee on Systematic Bacteriology has placed M. methanica on the list of nomina rejicienda as a nomen dubium et confusum (Opinion 63, Judicial Commission of the International Committee on Systematic Bacteriology 1986b; Wayne 1986). Instead, Methanosarcina barkeri was approved as the type species of the genus.

  • Methanococcus frisius (Blotevogel and Fischer 1989) was transferred to the genus Methanosarcina as Methanosarcina frisia comb. nov. (Blotevogel and Fischer 1989) and was subsequently assigned as a junior synonym to Methanosarcina mazei (Maestrojuán et al. 1992).

  • Methanococcus mazei (Barker 1936; Approved Lists 1980), formerly the type species of the genus Methanococcus, was transferred to the genus Methanosarcina as Methanosarcina mazei comb. nov. (Mah and Kuhn 1984a), while conserving the genus Methanococcus (Approved Lists, 1980) emend. Mah and Kuhn 1984a with Methanococcus vannielii (Approved Lists, 1980) as the type species (Opinion 62, Judicial Commission of the International Committee on Systematic Bacteriology 1986a).

  • Methanococcus halophilus (Zhilina 1984) (Validation List no. 14, 1984; effective publication: Zhilina 1983) was transferred to the genus Methanohalophilus as Methanohalophilus halophilus comb. nov. (Wilharm et al. 1991).

  • Methanohalophilus zhilinae (Mathrani et al. 1988) was transferred to the genus Methanosalsum as Methanosalsum zhilinae (Validation List no. 85, 2002; Effective publication: Boone and Baker 2001).

  • Methanohalophilus oregonensis (Liu et al. 1990) was transferred to the genus Methanolobus as Methanolobus oregonensis comb. nov. (Validation List no. 85, 2002; Effective publication: Boone 2001b).

  • Methanolobus siciliae (Stetter and König 1989 in Stetter 1989; Validation List no. 31, 1989) was transferred and emended as Methanosarcina siciliae (Ni et al. 1994).

  • The culture of Halomethanococcus doii (Validation List no. 26, 1988; Effective publication: Yu and Kawamura 1987) was lost.

Phylogenetic Structure of the Family and Its Genera

Figure 18.1 shows a maximum likelihood tree of the genera and species of the Methanosarcinaceae, showing the position of this family within the order Methanosarcinales (Boone et al. 2001b), which in addition contains the families Methanotrichaceae (Oren 2014) and the single-species family Methermicoccaceae. A neighbor joining tree (not shown) shows a similar topology. The genus Halomethanococcus with its species Halomethanococcus doii is not represented in the tree as the type strain and single isolate of this species were lost and are no longer available for study.

Fig. 18.1
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Phylogenetic reconstruction of the family Methanosarcinaceae based on 16S rRNA and created using the maximum likelihood algorithm RAxML (Stamatakis 2006). The sequence dataset and alignment were used according to the All-Species Living Tree Project (LTP) database (Yarza et al. 2010; http://www.arb-silva.de/projects/living-tree). Representative sequences from closely related taxa were used as out-groups. In addition, a 40 % maximum frequency filter was applied in order to remove hypervariable positions and potentially misplaced bases from the alignment. Scale bar indicates estimated sequence divergence. No 16S rRNA gene sequence has been published for the lost type strain and only described strain of Halomethanococcus doii

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Genome Analysis

At the time of writing (January 2014), the complete sequences of 10 isolates of Methanosarcinaceae were published. The lengths of these genomes vary between 2.01 Mbp (Methanohalophilus mahii) and 5.75 Mbp (Methanosarcina acetivorans). Plasmids were found in three out of these 10 genomes. The genome sequence data are summarized in Table 18.1 . The sequenced organisms include the type strains of Methanosarcina acetivorans, Methanococcoides burtonii, Methanohalophilus evestigatus, Methanohalophilus mahii, Methanomethylovorans hollandica, and Methanosalsum zhilinae. Other sequenced strains include Methanosarcina barkeri strain Fusaro and two isolates of Methanosarcina mazei (Gö1 and TUC). The latter strain was isolated from sediment samples from a hydroelectric power station reservoir in Brazil (Assis das Graças et al. 2013). Comparison of the genomes of different Methanosarcina species revealed extensive gene rearrangement within this genus (Maeder et al. 2006). Methanosarcina barkeri strain Fusaro and Methanosarcina acetivorans were used as model organisms for genome-scale metabolic reconstruction (Benedict et al. 2012; Gonneman et al. 2013; Kumar et al. 2011). An additional sequenced genome is that of the psychrophilic (optimal growth at 18 °C) “Methanolobus psychrophilus,” a name yet to be validly published (Chen et al. 2012; Zhang et al. 2008).

Table 18.1 Summary of the genomic information available for members of the Methanosarcinaceae as of November 2013
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Methanococcoides burtonii, isolated from a lake in Antarctica, has become a popular model organism for genomic, proteomic, and transcriptomic studies to elucidate the effect of low temperatures on growth of methanogenic Archaea. A microarray study of cells grown at 4 °C and 23 °C showed differential expression of more than 500 genes (Campanaro et al. 2011). Interestingly, the heat shock protein DnaK was expressed at the “optimal” temperature of 23 °C, showing that this temperature may be stressful to the cells (Goodchild et al. 2004a). The genome of Methanococcoides burtonii was, together with the even more psychrophilic Methanogenium frigidum (family Methanomicrobiaceae), compared with genomes of mesophilic methanogens. The encoded proteins of the psychrophilic species have a higher content of the neural polar amino acids glutamine and threonine and a lower content of leucine and other hydrophobic amino acids (Saunders et al. 2003).

Tools for the genetic manipulation of Methanosarcina spp. are now available. These include methods for liposome- and polyethylene glycol-mediated transformation, shuttle vectors that replicate in Methanosarcina acetivorans as well as in Escherichia coli, and methods for homologous recombination (Kohler and Metcalf 2012; Metcalf et al. 1997).

Phages

No viruses attacking members of the Methanosarcinaceae were yet documented. However, a 46,131 bp provirus was identified in the genome of Methanosarcina acetivorans. The sequence (43 mol% G+C) contains one tRNA gene (Krupovič et al. 2010).

Phenotypic Analyses

Methanosarcina Kluyver and van Niel 1936, 400(Approved Lists 1980)

Me.tha.no.sar.ci’na. L. n. methanum [from French n. méth(yle) and chemical suffix -ane], methane; N.L. pref. methano-, pertaining to methane; L. fem. sarcina, a package, bundle; N.L. fem. n. Methanosarcina, methane package, methane sarcina.

The cells are irregular spherical bodies, 1–3 μm in diameter, occurring alone or typically in clusters 20–100 μm or more in diameter. Occasionally, these bodies may aggregate to form large rafts more than 1 mm across. Sometimes large cysts are formed with a common outer wall surrounding individual coccoid cells. A life cycle involving these forms may occur. Some species may form gas vesicles. An outer heteropolysaccharide layer may be present external to the cell wall. The Gram stain is variable. Motility is seldom observed. Cells are strict anaerobes that obtain energy by the formation of methane from methanol, methylated amines, acetate (in some species), and H2/CO2 (in some species). Some isolates may grow on pyruvate or on carbon monoxide. Methanogenesis on formate has not been reported. The species are mesophilic to slightly thermophilic and prefer neutral pH values, and some can grow at seawater salinity (Boone and Mah 2001; Ni et al. 1994).

The mol% G+C of the DNA varies between 36 and 43.

Type species: Methanosarcina barkeri.

The description of the genus was emended by Barker (1956) and by Mah and Kuhn (1984a). At the time of writing (January 2014), the genus contained 11 species (Table 18.2 ):

  • Methanosarcina barkeri Schnellen 1947 (Approved Lists 1980) emend. Bryant and Boone 1987, emend. Maestrojuán et al. 1992) (Figs. 18.2 , 18.3 ).

  • Methanosarcina acetivorans Sowers et al. 1986 (Validation List no. 20, 1986; Effective publication: Sowers et al. 1984). This is a marine isolate that has an osmotically fragile protein cell wall. Motility was not observed, but genes coding for flagellins and chemotaxis genes are present in the genome (Galagan et al. 2002).

  • Methanosarcina baltica von Klein et al. 2002 (Validation List no. 85, 2002), emend. Singh et al. 2005.

  • Methanosarcina horonobensis Shimizu et al. 2011, isolated from a deep subsurface Miocene formation.

  • Methanosarcina lacustris Simankova et al. 2002. (Validation List no. 85, 2002; Effective publication: Simankova et al. 2001).

  • Methanosarcina mazei (Barker 1936) Mah and Kuhn 1984a, comb. nov. (basonym, Methanococcus mazei Barker 1936 (Approved Lists 1980)). In unshaken cultures, this species can grow as large lamina (Mayerhofer et al. 1992). The species described as Methanosarcina frisia (Blotevogel and Fischer 1989) (basonym, Methanococcus frisius; Blotevogel et al. 1986) is considered a junior subjective synonym of M. mazei (Maestrojuán et al. 1992). Methanosarcina barkeri Gö1 is closely related to M. frisia (Eggen et al. 1992).

  • Methanosarcina semesiae Lyimo et al. 2000 is a dimethyl sulfide-utilizing methanogen from mangrove sediment.

  • Methanosarcina siciliae (Stetter and König 1989; Ni et al. 1994, comb. nov. (basonym, Methanolobus siciliae Stetter and König 1989, emend. Elberson and Sowers 1997) was first isolated from the sediments of a submarine canyon (Fig. 18.4 ). Originally described as non-aceticlastic, aceticlastic strains are known as well.

  • Methanosarcina soligelidi Wagner et al. 2013, a desiccation- and freeze-thaw-resistant methanogen isolated from Siberian permafrost soil.

  • Methanosarcina thermophila Zinder et al. 1985, a moderately thermophilic acetotrophic organism that grows in large clusters with chaotically dispersed division planes in clusters (Fig. 18.5 ) that is unable to use H2/CO2. The type strain was isolated from a laboratory-scale thermophilic digestor (Zinder and Mah 1979).

  • Methanosarcina vacuolata Zhilina and Zavarzin 1987a, a species known for the production of gas vesicles (Zhilina and Zavarzin 1979).

Fig. 18.2
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Methanosarcina barkeri strain MS (Courtesy of D. Boone; reproduced from Whitman et al. 2006)

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Fig. 18.3
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Thin section of aggregates of Methanosarcina barkeri (Courtesy of Henry Aldrich, Department of Microbiology and Cell Science, University of Florida, Gainesville, FL. Reproduced from Kendall and Boone 2006)

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Table 18.2 Characteristics of the species classified within the genus Methanosarcina
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Fig. 18.4
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Electron micrograph of Methanosarcina siciliae (Courtesy of Henry Aldrich, Department of Microbiology and Cell Science, University of Florida, Gainesville, FL. Reproduced from Kendall and Boone 2006)

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Fig. 18.5
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Electron micrograph of Methanosarcina thermophila (Courtesy of Henry Aldrich, Department of Microbiology and Cell Science, University of Florida, Gainesville, FL. Reproduced from Kendall and Boone 2006)

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Further comments:

  • Under certain conditions, clusters of Methanosarcina can disaggregate into single cells. Transfer of M. barkeri, M. acetivorans, M. thermophila, and M. vacuolata from 0.4 M to 1 M NaCl results in growth as single cells rather than in aggregates. Aggregates are formed again after transfer to salt concentrations below 0.2 M (Sowers 1995; Sowers et al. 1993).

  • Gas vesicles can be formed not only by M. vacuolata but also by some strains of M. barkeri. M. barkeri strain FR-1 (DSM 2256) isolated from sewage sludge is such a gas-vacuolated strain (Archer and King 1983, 1984; Maestrojuán et al. 1992). Note also the presence of gas vesicles in the cells shown in Fig. 18.6 , in a culture assigned to M. mazei, a species not further known for gas vesicle production.

Fig. 18.6
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Electron micrograph of a Methanosarcina showing gas vesicles (designated in Kendall and Boone (2006) as Methanosarcina mazei, a species not known for gas vesicle formation) (Courtesy of Donna Williams and Henry Aldrich, Department of Microbiology and Cell Science, University of Florida, Gainesville, FL. Reproduced from Kendall and Boone 2006)

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Halomethanococcus Yu and Kawamura 1988 (Validation List no. 26, 1988; Effective publication: Yu and Kawamura 1987, 309).

Ha.lo.me.tha.no.coc’cus. Gr. n. hals, halos, salt; N.L. n. methanum [from French n. méth(yle) and chemical suffix -ane], methane; N.L. pref. methano-, pertaining to methane; N.L. masc. n. coccus (from Gr. n. kokkos) a grain or berry; N.L. masc. n. Halomethanococcus the salt methane coccus.

The single isolate assigned to this species is no longer available for study. The strain, isolated from the sediment of a saltern pond in California, was described as consisting of obligate halophilic pleomorphic nonmotile cocci that occur singly or in small irregular clumps. It requires >1.8 M NaCl for growth and can grow up to 3.6 M. Methylated amines and methanol are catabolized with the formation of methane; H2/CO2, acetate, and formate are not used for methanogenesis. Optimal growth was reported at 35–37 °C and at neutral pH.

The mol% G+C of the DNA of the lost type strain of the single species is 43.2.

At the time of writing (January 2014), the genus contained one species: Halomethanococcus doii (Yu and Kawamura 1987). The properties of the genus, as summarized in Table 18.3 , are very similar to those of Methanohalophilus (Paterek and Smith 1988).

Table 18.3 Characteristics of the species classified within the genera Halomethanococcus, Methanimicrococcus, Methanococcoides, and Methanohalobium
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Methanimicrococcus corrig. Sprenger et al. 2000, 1998

Me.tha.ni.mi.cro.coc’cus. N.L. n. methanum [from French n. méth(yle) and chemical suffix -ane], methane; N.L. pref. methano-, pertaining to methane; Gr. adj. mikros small; N.L. masc. n. coccus (from Gr. masc. n. kokkos, grain, seed), coccus; N.L. masc. n. Methanimicrococcus a small methane-forming coccus.

The single species of this genus, isolated from the hindgut of a cockroach, consists of irregular cocci with a mean diameter of 0.8 μm occurring singly or in clusters. The cells are susceptible to hyposmotic lysis and lyse also during the Gram-staining procedure. The mode of energy generation of this obligately anaerobic species differs from that of all other genera of the Methanosarcinaceae as hydrogen and methanol or methylated amines are required simultaneously. Coenzyme M is required for growth, as are additional organic nutrients (acetate, yeast extract, tryptic soy broth).

The mol% G+C of the DNA has not been reported.

At the time of writing (January 2014), the genus contained one species: Methanimicrococcus blatticola (Sprenger et al. 2000). Its properties are summarized in Table 18.3 .

Methanococcoides Sowers and Ferry 1985(Validation List no. 17, 1985; Effective Publication:Sowers and Ferry 1983, 688)

Me.tha.no.coc.co’i.des. N.L. masc. n. Methanococcus a prokaryote genus name; L. suff –oides (from Gr. suff. –eides, from Gr. n. eidos, that which is seen, form, shape, figure), resembling, similar. N.L. neut. n. Methanococcoides, organism similar to Methanococcus.

Cells are irregular cocci, occurring singly, in pairs, or in clusters, and stain Gram negative. Some species are motile by means of monotrichous flagella. They are strict anaerobes that obtain energy from the conversion of methylated amines; some species can also use methanol. H2/CO2, acetate, and formate are not used for methanogenesis. Optimal growth is achieved at mesophilic or at lower temperatures and at neutral pH. Sodium and magnesium are required for growth (Sowers 2001; Sowers and Ferry 1983).

The mol% G+C of the DNA varies between 40 and 42.

Type species: Methanococcoides methylutens.

At the time of writing (January 2014), the genus contained 3 species (Table 18.3 ):

  • Methanococcoides methylutens (Validation List no. 17, 1985; Effective publication: Sowers and Ferry 1983, 1985) (Figs. 18.7 , 18.8 ). Another strain that can probably be classified within the species is strain MM1 isolated from mangrove sediment in Tanzania. This isolate grows rapidly (minimal doubling time 3.2 h) on methanol and on trimethylamine (Lyimo et al. 2009).

  • Methanococcoides alaskense, a moderately psychrophilic isolate from anoxic marine sediments in Alaska (Singh et al. 2005).

  • Methanococcoides burtonii (Validation List no. 45, 1993; Effective publication: Franzmann et al. 1992), a moderately psychrophile isolated from the hypolimnion of a lake in Antarctica.

Fig. 18.7
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Phase-contrast photomicrograph of Methanococcoides methylutens. Bar = 10 μm (Courtesy of K. Sowers, Center for Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, MD. Reproduced from Kendall and Boone 2006)

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Fig. 18.8
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Thin section transmission electron micrograph of Methanococcoides methylutens stained with uranyl acetate. Bar = 1 μm (Courtesy of K. Sowers, Center for Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, MD. Reproduced from Kendall and Boone 2006)

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A coccoid methylotrophic methanogen named “Methanococcoides euhalobius” was isolated from an oil bed in Russia (Charakhchyan et al. 1989; Obraztsova et al. 1984; 1987). This name was never validated.

Methanohalobium Zhilina and Zavarzin(Validation List no. 24, 1988; Effective Publication:Zhilina and Zavarzin 1987, 467)

Me.tha.no.ha.lo’bi.um. N.L. n. methanum [from French n. méth(yle) and chemical suffix -ane], methane; N.L. pref. methano-, pertaining to methane; Gr. n. hals, halos salt; Gr. masc. n. bios life, N.L. neut. n. Methanohalobium methane-producing organism living in salt.

Cells are polygonal flat or irregular nonmotile spheroids occurring singly or in small aggregates. The result of the Gram stain is variable. They are obligate anaerobes using methylated amines, acetate, formate, and H2/CO2 with the formation of methane. Methanol can be used at low concentrations. Optimal growth is achieved at 4.3 M NaCl and 40–55 °C.

The mol% G+C of the DNA of the type strain of the single species is 36.4.

At the time of writing (January 2014), the genus contained one species: Methanohalobium evestigatum corrig. Zhilina and Zavarzin 1987b; Zhilina and Svetlichnaya 1989) (Fig. 18.9 ). Its properties are summarized in Table 18.3 .

Fig. 18.9
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Methanohalobium evestigatum. (a) Cells and aggregates, anoptral contrast. Bar = 5 μm. (b) Ultrathin section of late exponential phase cells. Layers of the envelope slip from the cell surface. Nuclear region and star-shaped granules (possible glycogen) are present. Bar = 0.5 μm (Courtesy of T. Zhilina; reproduced from Whitman et al. 2006)

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Methanohalophilus Paterek and Smith 1988, 122

Me.tha.no.ha.lo’phi.lus. N.L. n. methanum [from French n. méth(yle) and chemical suffix -ane], methane; N.L. pref. methano-, pertaining to methane; Gr. n. hals, halos, salt; N.L. masc. adj. philus (from Gr. masc. adj. philos), friend, loving; N.L. masc. n. Methanohalophilus salt-loving methanogen.

Cells are irregular nonmotile cocci, ∼1 μm in diameter, occurring singly or in small clumps and staining Gram negative. They are easily lysed by detergents or by hypotonic shock. Growth with methane production is supported by methylated amines and by methanol, but methanol is toxic at high concentrations; H2/CO2, formate, and acetate do not support growth. They are moderately halophilic, fastest growth being recorded at NaCl concentrations between 1.0 and 2.5 M, near-neutral pH, and mesophilic temperatures. Some strains require vitamins for growth (Boone 2001a).

The mol% G+C of the DNA varies between 41 and 44.

Type species: Methanohalophilus mahii.

At the time of writing (January 2014), the genus contained 3 species (Table 18.5 ):

  • Methanohalophilus mahii (Paterek and Smith 1985, 1988), the type species of the genus.

  • Methanohalophilus halophilus (basonym, Methanococcus halophilus) (Zhilina 1984). The cells of this species are surrounded by a polysaccharide capsule (Wilharm et al. 1991). The fine structure of this polygonal-shaped organism was studied by Cherny et al. (1986).

  • Methanohalophilus portucalensis (Boone et al. 1993).

Methanohalophilus oregonensis (Liu et al. 1990) has been transferred to the genus Methanolobus as Methanolobus oregonensis comb. nov. (Boone 2001b).

An additional isolate assigned to this genus is “Methanohalophilus euhalobius” strain 283, earlier named “Methanococcoides euhalobius.” This organism, isolated from saline subsurface water of an oil field in Russia, was reported to grow optimally at 28–37 °C, pH 6.8–7.3, and 1 M NaCl (Davidova et al. 1997; Obraztsova et al. 1984). The moderately halophilic strain SF1, isolated from a solar saltern, may also belong to the genus Methanophilus. This isolate of irregular cocci growing singly or in clumps, using only methanol and methylated amines as methanogenic substrates, grows optimally (doubling time 10.2 h) at 37 °C, pH 7.4, and 2.1 M NaCl, in media supplemented with yeast extract and rumen fluid. The mol% G+C of its DNA is 41 (Mathrani and Boone 1985).

Methanolobus König and Stetter 1983(Validation List no. 10, 1983; Effective Publication:König and Stetter 1982, 488)

Me.tha.no.lo’bus. N.L. n. methanum [from French n. méth(yle) and chemical suffix -ane], methane; N.L. pref. methano-, pertaining to methane; L. masc. n. lobus ball, lobe; N.L. masc. n. Methanolobus, methane (−producing) lobe.

Cells are irregular coccoid, are surrounded by an S-layer protein wall, and stain Gram negative. Some species are motile. They are strictly anaerobic Archaea that produce methane from methanol, methylated amines, and (some species) dimethyl sulfide. H2/CO2, formate, and acetate are not used for energy generation. They are mesophilic to slightly thermophilic and generally grow fastest at seawater salinity.

The mol% G+C of the DNA varies between 39.2 and 42.4.

Type species: Methanolobus tindarius.

At the time of writing (January 2014), the genus contained 7 species (Boone 2001b; Table 18.4 ):

  • Methanolobus tindarius (the type species) (Oremland and Boone 1994)

  • Methanolobus bombayensis (Kadam et al. 1994)

  • Methanolobus oregonensis (Validation List no. 85, 2002; Effective publication: Boone 2001b) (basonym, Methanohalophilus oregonensis (Liu et al. 1990); Fig. 18.10 )

  • Methanolobus profundi (Mochimaru et al. 2009)

  • Methanolobus taylorii (Oremland and Boone 1994)

  • Methanolobus vulcani (Validation List no. 31, 1989; Effective publication: Stetter et al. 1989 in Stetter 1989, emend. Kadam and Boone 1995)

  • Methanolobus zinderi (Doerfert et al. 2009)

Fig. 18.10
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(a) Electron micrograph of Methanolobus oregonensis cells. (b) Single cell of Methanolobus oregonensis (Courtesy of Henry Aldrich, Department of Microbiology and Cell Science, University of Florida, Gainesville, FL. Reproduced from Kendall and Boone 2006)

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Table 18.4 Characteristics of the species classified within the genus Methanolobus
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Table 18.5 Characteristics of the species classified within the genera Methanohalophilus, Methanomethylovorans, and Methanosalsum
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In addition, there is an isolate designated “Methanolobus psychrophilus” strain R15 (JCM 14818, CGMCC 1.5060). This psychrophilic isolate (best growth at 18 °C, not growing above 25 °C) originated from cold wetland of the Tibetan Plateau. Its cells are elliptical, are 0.9–1.0 × 1.0–1.2 μm in size, are surrounded by a capsule, and are motile by 1–2 polar flagella. Methanol, methylamine, and methyl sulfide support growth with methanogenesis. Optimal growth was recorded in the presence of 0.2–25 M NaCl and neutral pH. Yeast extract is stimulatory. The mol% G+C of the DNA is 44.9 (Zhang et al. 2008). The proposed name has not yet been validated.

Methanolobus siciliae (Ni and Boone 1991) has been transferred to the genus Methanosarcina as Methanosarcina siciliae comb. nov. (Ni et al. 1994).

Methanomethylovorans Lomans et al. 2004(Validation List no. 96, 2004; Effective Publication:Lomans et al. 1999, 3649)

Me.tha.no.me.thy.lo.vo’rans. N.L. n. methanum [from French n. méth(yle) and chemical suffix -ane], methane; N.L. pref. methano-, pertaining to methane; N.L. n. methylum (from French méthyle, back-formation from French méthylène, coined from Gr. n. methu, wine and Gr. n. hulê, wood), the methyl group. N.L. pref. methylo- pertaining to the methyl radical; L. part. adj. vorans, devouring; N.L. fem. part. adj. Methanomethylovorans methane-producing, methyl group consuming.

Cells are irregular nonmotile cocci, staining Gram negative, that may occur in aggregates. They are mesophilic or slightly thermophilic. They are strict anaerobes that produce methane from methylated amines and methanol. Methyl sulfides are catabolized by some species. H2/CO2 and acetate do not support growth.

The mol% G+C of the DNA varies between 37.6 and 41.8.

Type species: Methanomethylovorans hollandica.

At the time of writing (January 2014), the genus contained two species (Table 18.5 ):

  • Methanomethylovorans hollandica (Lomans et al. 1999). Its cells are not lysed by 1 % SDS.

  • Methanomethylovorans thermophila (Jiang et al. 2005). Cells are lysed by 0.1 % SDS.

The isolation of a third species, “Methanomethylovorans victoriae” strain TM, was mentioned by Jiang et al. (2005), but no further information is currently available about this organism.

Methanosalsum Boone and Baker 2002(Validation List no. 82, 2002; Effective Publication:Boone and Baker 2001, 287)

Me.tha.no.sal’sum. N.L. n. methanum [from French n. méth(yle) and chemical suffix -ane], methane; N.L. pref. methano-, pertaining to methane; L. neut. adj. salsum salted, salty. N.L. neut. n. Methanosalsum the salty methane (bacterium).

Cells are irregular angular cocci that occasionally occur in tetrads or in clumps. They have an S-layer cell wall, are motile by 1–2 flagella, and stain Gram negative. They are strict anaerobes that produce methane from methylated amines, methanol, and dimethyl sulfide. Growth is most rapid at 35–45 °C (range 20–50), at alkaline pH (8.7–9.5), and in the presence of 0.4–0.7 M NaCl.

The mol% G+C of the DNA of the type strain of the single species is 39.2.

At the time of writing (January 2014), the genus contained one species: Methanosalsum zhilinae (Boone and Baker 2001) – basonym, Methanohalophilus zhilinae (Mathrani et al. 1988). Its properties are summarized in Table 18.5 .

Isolation, Enrichment, and Maintenance Procedures

As for all methanogenic Archaea, the cultivation of members of the Methanosarcinaceae requires the use of reduced media and strictly anaerobic techniques. In enrichment media, antibiotics inhibiting bacteria can be included such as penicillin, cycloserine, and vancomycin (Liu et al. 1990; Sowers 2001; Sowers and Ferry 1983). For the preparation of solidified media, purified agar such as Noble agar is preferred (Doerfert et al. 2009; Sowers 2001).

For short-term maintenance, regular subculturing is generally satisfactory (Hippe 1984). For Methanococcoides, transferring every 3 months on agar slants or in liquid medium followed by storage in the dark at room temperature was recommended; for the psychrophilic M. burtonii, lower temperatures are preferred. For long-term preservation, cells can be frozen in liquid medium supplemented with glycerol. Anoxic suspensions of cells with 5 % glycerol are frozen at a rate of 1 °C/min to −40 °C and then stored at liquid nitrogen temperature (Boone 1995; Kendall and Boone 2006; Tumbula et al. 1995).

Physiological and Biochemical Features

The Methanosarcinaceae share many biochemical and physiological properties with the other families of methanogenic Archaea (Hedderich and Whitman 2006; Whitman et al. 2006). But some members of the family possess unusual modes of energy generation and metabolism beyond the use of H2/CO2, methanol, and trimethylamine:

  • Many Methanosarcina species split acetate to methane and carbon dioxide (Ferry 1992), a property shared only with the genus Methanothrix.

  • Two thermophilic Methanosarcina strains, Methanosarcina thermophila TM-1T and Methanosarcina sp. SO-2P (DSM 11429), can grow on methanol and H2/CO2 which are used simultaneously (mixotrophy). Accordingly, Methanosarcina spp. may be more important H2 oxidizers than generally assumed (Mladenovska and Ahring 1997).

  • Methanosarcina acetivorans C2AT can grow on carbon monoxide, not producing methane but instead forming acetate and formate according to 4 CO + 4 H2O → CH3COO– + 2 HCO3 – + 3H+; ΔGo' = −164.6 kJ/mol, and CO + H2O → HCOO– + H+; ΔGo' = −16 kJ/mol. Growth on CO to high densities is possible with a doubling time of ∼24 h (Rother and Metcalf 2004).

  • Methanococcoides sp. strain NaT1, a close relative of M. methylutens, can grow on tetramethylammonium using an inducible tetramethylammonium: coenzyme M methyltransferase. Cells grown on trimethylamine do not show this activity (Asakawa et al. 1998).

  • After a long adaptation period, Methanosarcina barkeri strain Fusaro can slowly grow on pyruvate (Bock et al. 1994).

  • Some Methanosarcina species (M. barkeri, M. mazei, M. thermophila) can dehalogenate certain halogenated carbon compounds. M. mazei S-6 dechlorinates chloroform. The first intermediate product is methylene chloride.14C-labeled chloroform yielded14CO2 and not14CH4 as expected for a reductive process (Mikesell and Boyd 1990). However, reductive dechlorination of trichloroethylene (to ethylene via dichloroethylene and vinyl chloride) was found in Methanosarcina thermophila (Jablonski and Ferry 1992), and trichlorofluoromethane (CFC-11, Freon) is dehalogenated by M. barkeri (Krone and Thauer 1992).

Methanococcoides burtonii uses a modified Calvin cycle for autotrophic CO2 fixation (Goodchild et al. 2004b). It shows activity of ribulose-1,5-bisphosphate carboxylase/oxygenase, and the catalytic properties of the enzyme were documented (Alonso et al. 2009).

Methanosarcina barkeri can use N2 as nitrogen source for growth, as shown by growth experiments and by measuring incorporation of 15N2. The standard acetylene reduction test is not suitable as an assay for nitrogenase activity in this organism as acetylene is toxic to methanogens and cannot be used at concentrations >100 micromol per liter (Bomar et al. 1985; Lobo and Zinder 1988). M. barkeri synthesizes molybdenum-containing nitrogenase (resembling the enzyme of Clostridium pasteurianum) as well as vanadium-containing nitrogenase (resembling that of Anabaena) (Chien et al. 2000; Scherer 1989).

Methanococcoides methylutens and Methanolobus tindarius accumulate glycogen as a storage polymer (König et al. 1985; Maitra et al. 2001). Methanosarcina strains may form polyphosphate granules, and “Methanosarcina frisia” can accumulate polyphosphate up to 14 % of its dry weight (Rudnick et al. 1990; Scherer and Bochem 1983).

Similar to some methanogens belonging to other families (Methanococcus voltae, Methanothermobacter thermautotrophicus), members of the Methanosarcinaceae may be sensitive to light, as documented for Methanosarcina acetivorans. Wavelengths of 370–430 are especially inhibitory (Olson et al. 1991).

Methanosarcina species typically have a thick (∼500 nm) cell wall composed of an acidic heteropolysaccharide (Balch et al. 1979). Methanosarcina acetivorans is exceptional as it only possesses a thin protein cell wall, showing a hexameric S-layer pattern. The protein subunits form a negatively charged molecular sieve that presents both a charge and a size barrier (Arbing et al. 2013; Sowers et al. 1984). The Methanosarcina mazei S-layer and surface proteins have O-glycosylated threonine and tyrosine, being the first reported case of tyrosine glycosylation in Archaea (Leon et al. 2012). An outer layer of heteropolysaccharide composed of galactosamine, glucose, mannose, and glucuronic or galacturonic acid is present in many Methanosarcina species (Boone and Mah 2001; Zhilina and Zavarzin 1987a). For the cell wall exopolymer of different strains of Methanosarcina, composed of N-acetyl-D-galactosamine and D-glucuronic (or D-galacturonic) acid at 2:1 ratio, the following structure was proposed: [→4]-β-D-GlcUA(1→3)-D-GalNAc(1→3 or 4) D-GalNAc(1→] (Kreisl and Kandler 1986). Methanosarcina mazei strain LYC, isolated from alkaline sediment at an oil exploration drilling site, produces an enzyme dissolving the heteropolysaccharide component of the cell wall. At the beginning of the exponential growth stage, cell aggregates spontaneously disperse as a result of the action of this enzyme (Liu et al. 1985).

Members of the genera Methanolobus and Methanosalsum also have S-layer protein cell walls (Boone 2001b; Boone and Baker 2001). Methanococcoides euhalobius has a wall polysaccharide with glucose and mannose in the ratio 1.5:1 (Charakhch’yan et al. 1991), and Methanohalophilus halophilus possesses a cell envelope consisting of a 3–6-nm-thick cell wall surrounded by a 10–15-nm-thick mucopolysaccharide layer (Cherny et al. 1986).

The core lipids of the Methanosarcinaceae are based on C20,C20 diethers, mainly 2,3-di-O-phytanyl-sn-glycerol, with myo-inositol, ethanolamine, and glycerol as common polar head groups (Balch et al. 1979; Boone et al. 2001a; Langworthy et al. 1982). A report of the occurrence of C20C25 core lipids in Methanosarcina barkeri DSM 800T and in Methanosarcina mazei DSM 2278 (Grant et al. 1985) remains to be confirmed. Instead, 3-hydroxydiether analogs of phosphatidylglycerol, phosphatidylinositol, phosphatidylserine, and phosphatidylethanolamine were identified in Methanosarcina mazei, in Methanosarcina soligelidi, and in other Methanosarcina species (Sprott et al. 1994; Wagner et al. 2013). The dominant phospholipid of Methanohalophilus halophilus was reported to be the diether derivative of phosphoglycerogluconolactone (Osipov et al. 1984; Wilharm et al. 1991). The core lipids of Methanococcoides methylutens are 2,3-diphytanyl glycerol diethers (archaeol) and an unidentified core lipid (Sowers and Ferry 1983).

The lipids of the psychrophilic Methanococcoides burtonii are unusual as they contain unsaturated archaeol derivatives. The main phospholipids are archaeol phosphatidylglycerol, archaeol phosphatidylinositol, hydroxyarchaeol phosphatidylglycerol, and hydroxyarchaeol phosphatidylinositol. Unsaturated analogs were found in all phospholipid classes. The degree of unsaturation was higher in cells grown at 4 °C than at 23 °C (Nichols and Franzmann 1992; Nichols et al. 2004).

The main neutral lipids of Methanosarcina barkeri, Methanolobus bombayensis, and Methanosarcina mazei are mainly 25-carbon isoprenoids with up to five double bonds (Langworthy et al. 1982; Schouten et al. 1997).

Many species of Methanosarcinaceae are halophilic or halotolerant, and therefore studies have been made of their mode of osmotic adaptation. Methanohalophilus portucalensis cells contain glycine betaine as the main organic osmolyte. Glycine betaine can be taken up from the medium if available (Lai et al. 2000), but de novo biosynthesis is possible as well by stepwise methylation of glycine with sarcosine and dimethylglycine as intermediates, using S-adenosylmethionine as the donor of the methyl groups and involving multiple methyltransferase enzymes present in a complex of four proteins (Chen et al. 2009; Lai and Lai 2011; Lai et al. 2006).

Methanohalophilus strain FDF1, a strain that grows on methanol, trimethylamine, or dimethyl sulfide at NaCl concentrations between 1.2 and 2.9 M, produces multiple organic osmotic solutes: glycine betaine, N ε-acetyl-β-lysine, and β-glutamine. When grown on methanol, cells in addition produce α-glucosylglycerate, but its concentration is not regulated according to the medium salinity (Robertson et al. 1992). The mode of biosynthesis of the osmotic solutes was elucidated by NMR analysis following labeling with13C methanol. Glutamate and β-glutamine are synthesized via a partial oxidative Krebs pathway, glycine betaine is derived from glycine produced from serine, and N ε-acetyl-β-lysine is made from α-lysine made by the diaminopimelate pathway (Roberts et al. 1992). In addition to these organic solutes, K+ ions are important in osmotic adaptation of Methanohalophilus (Lai and Gunsalus 1992).

Methanosarcina spp. (M. barkeri, M. mazei, M. thermophila, M. acetivorans, M. vacuolata) use glycine betaine, α-glutamate, N ε-acetyl-β-lysine, and K+ as compatible solutes for osmotic adaptation (Sowers and Gunsalus 1995). In Methanosarcina mazei Gö1 N ε-acetyl-β-lysine can be substituted by glutamate and alanine: following deletion of the genes that encode lysine-2,3-aminomutase and β-lysine acetyltransferase, an increase in glutamate and alanine pools was observed to 18 % of total solute pool, and their concentrations were regulated according to the salinity (Saum et al. 2009).

The biosynthetic pathway of α-glucosylglycerate was studied in Methanococcoides burtonii. It is made from GDP-glucose and 3-phosphoglycerate by the action of glucosyl-3-phosphoglycerate synthase and glucosyl-3-phosphoglycerate phosphatase (Costa et al. 2006).

Members of the Methanosarcinaceae tested for sensitivity to different antibiotics (Methanosarcina baltica, Halomethanococcus doii, Methanomethylovorans thermophila, Methanohalophilus portucalensis, Methanolobus profundi, and the moderately halophilic strain SF1) are resistant to ampicillin, carbenicillin, cycloserine, erythromycin, kanamycin, penicillin, and vancomycin (Boone et al. 1993; Jiang et al. 2005; Mathrani and Boone 1985; Mathrani et al. 1988; Mochimaru et al. 2009; von Klein et al. 2002; Yu and Kawamura 1987). Penicillin and cycloserine have been included in enrichment media that led to the isolation of Methanolobus oregonensis (Liu et al. 1990) and other members of the Methanosarcinaceae. Most strains are sensitive to chloramphenicol, but Methanosarcina baltica is not inhibited (von Klein et al. 2002). The reaction to tetracycline varies: Methanohalophilus portucalensis and halophilic strain SF1 are resistant (Boone et al. 1993; Mathrani and Boone 1985), but Methanomethylovorans thermophila and Methanohalophilus zhilinae are sensitive (Jiang et al. 2005; Mathrani et al. 1988). Methanolobus profundi grows slowly in the presence of 100 μg/ml tetracycline (Mochimaru et al. 2009).

Ecology

Members of the family Methanosarcinaceae have been found in a wide range of anoxic habitats: aquatic sediments (freshwater, marine, as well as hypersaline), anaerobic sewage digestors, and more (Boone et al. 2001a; see also Tables 18.2 , 18.3 , 18.4 , and 18.5 ). They are relatively rare in the digestive tracts of animals, although Methanosarcina barkeri-like cultures have been isolated from sheep rumen (Jarvis et al. 2000), Methanimicrococcus was found in the cockroach hindgut (Sprenger et al. 2000), and Methanosarcina sp. was recovered from the human periodontal pocket (Robichaux et al. 2003).

The distribution of the Methanosarcinaceae in nature is to a large extent determined by their ability to obtain energy from substrates not or seldom used by other methanogenic Archaea – acetate, methylated amines, and methyl sulfides – as well as the potential to grow at salinities too high to support growth of members of the other methanogen families.

The only genus except for Methanosarcina that can use acetate as the energy source with the formation of methane is Methanothrix (family Methanotrichaceae) (Oren 2014). The result of the competition between these two groups of acetoclastic methanogens is largely determined by the available acetate concentrations. At high concentrations, Methanosarcina has the advantage of higher growth rates; at low concentrations, Methanothrix takes over, thanks to its higher affinity for the substrate (Clarens and Moletta 1990; Conklin et al. 2006).

With the exception of Methanosarcina soligelidi, all species of Methanosarcinaceae grow on methylated amines. Trimethylamine and other methylated amines are formed during the anaerobic degradation of glycine betaine, a widespread osmotic solute in halophilic cyanobacteria and in other prokaryotes that inhabit hypersaline environments. Therefore, it is not surprising that those methanogens found at the highest salt concentrations (genera Methanohalobium, Methanohalophilus, Methanosalsum, and the lost single isolate of the genus Halomethanococcus) all use methylated amines as substrates for energy generation (McGenity 2010; Zhilina 1986). Also thermodynamically energy generation from methylated amines is much more favorable that methanogenesis from H2/CO2 and from acetate, and this may explain why nearly no truly halophilic methanogens have yet been isolated on the latter substrates (Oren 1999, 2011). Another methanogenic substrate derived from the degradation of an organic osmotic solute is dimethyl sulfide, formed during the anaerobic breakdown of dimethylsulfoniopropionate, produced by many marine algae. Studies on the metabolism of reduced methylated sulfur compounds in anaerobic sediments led to the isolation of Methanolobus taylorii (Kiene et al. 1986; Oremland and Boone 1994), but as documented in Tables 18.2 , 18.4 , and 18.5 , many other members of the family produce methane from methyl sulfides. Also in freshwater environments are dimethyl sulfide-metabolizing methanogens widespread, as shown by the dominance of Methanomethylovorans hollandica-like organisms as the organisms responsible for the degradation of dimethyl sulfide and methanethiol in various freshwater sediments in the Netherlands (Lomans et al. 2001).

The family Methanosarcinaceae does not contain any extreme thermophiles, but some species can grow at temperatures up to 55–60 °C. Methanosarcina thermophila tolerates up to 55 °C, Methanohalobium evestigatum has its optimum at 40–55 °C and tolerates up to 60 °C, Methanolobus zinderi grows optimally at 40–50 °C, and Methanomethylovorans thermophila grows at up to 58 °C. The methanogenic community in an anaerobic thermophilic bioreactor operated at 55 °C was dominated by organisms closely related to Methanomethylovorans hollandica as assessed using culture-independent methods (Roest et al. 2005). 16S rRNA gene clones affiliated with Methanomethylovorans thermophila (as well as clones related to Methanomassiliicoccus luminyensis and Methanococcus aeolicus) were retrieved from hot spring microbial mats from a geothermal region in Romania (Coman et al. 2013), and phylotypes of Methanomethylovorans (as well as Methanothermobacter, Methanoculleus, and Methanothrix) were found in a high-temperature (75 °C) petroleum reservoir (Lan et al. 2011a).

Members of the Methanospirillaceae are also found in cold environments. Methanococcoides burtonii (minimum growth temperature ∼2 °C, optimum 23 °C) was isolated from Ace Lake, Antarctica (Franzmann et al. 1992). Another cold-tolerant strain is “Methanolobus psychrophilus” R15 from wetlands of the Tibetan Plateau. This isolate (JCM 14818, CGMCC 1.5060) grows best at 18 °C, does not tolerate temperatures above 25 °C, and uses methanol, trimethylamine, and dimethyl sulfide as substrates (Zhang et al. 2008). The species name was not yet validly published. Strains related to Methanosarcina mazei, to Methanosarcina lacustris, and to Methanomethylovorans hollandica able to grow at 5–6 °C were isolated from tundra wetland soil, from a Russian pond polluted with paper-mill waste, from anoxic sediments of a Swiss lake, and from an anaerobic digestor for cattle manure operated at 6 °C (Simankova et al. 2003).

At the high pH end, Methanosalsum zhilinae, an isolate from the Wadi El Natrun, Egypt, soda lakes, grows up to pH 10.0 with an optimum at 8.7–9.5 (Boone and Baker 2001; Mathrani et al. 1988), and Methanolobus oregonensis, obtained from a saline alkaline aquifer, has its pH optimum at 8.2–9.2 and can grow up to pH 9.4 (Liu et al. 1990). An alkaliphilic Methanosarcina was isolated from Lonar crater lake, India. It grows on acetate, methanol, and methylated amines up to pH 9.5 (optimally at pH 9.0) (Thakker and Ranade 2002). No further information was found about this isolate. A 16S rRNA gene clone library from Lonar crater lake sediments yielded sequences related to Methanolobus oregonensis (Antony et al. 2012). Another alkaliphilic strain, closely related to Methanosarcina mazei, growing optimally at pH 8.5 and tolerating pH values up to 9.5 was isolated from cow dung in Sichuan, China (Qian et al. 2012).

A large number of additional culture-independent studies have yielded 16S rRNA gene sequences affiliated with the Methanosarcinaceae, as shown by the following examples:

  • Methanohalophilus, Methanolobus, and Methanosarcina sequences were found in gas industry pipelines in the USA (Zhu et al. 2003).

  • Methanolobus and Methanoculleus sequences were predominant in the archaeal communities of saline gas field formation fluids in Lower Saxony, Germany (Ehinger et al. 2009).

  • Sequences affiliated with the termite midgut methanogen Methanimicrococcus blatticola were found, together with Methanobrevibacter, Methanoculleus, and Methanosphaera sequences, in a thermophilic municipal biogas plant (Weiss et al. 2008).

  • Methanosarcina sequences (16S rRNA and mcrA (methyl-CoM reductase)) dominated in an anaerobic sequential batch reactor operated with a short hydraulic retention time (Ma et al. 2013).

  • Methanosarcina 16S rRNA sequences were retrieved from deep South African gold mines (Takai et al. 2001).

  • Methanimicrococcus sequences were detected among other groups of methanogens in the rumen of cows fed with alfalfa hay or triticale straw (Kong et al. 2013).

  • Methanomethylovorans was found together with Methanolinea in recycled injection water and high-temperature petroleum reservoirs at an oil field, as well as in the anaerobic tank of a water treatment plant for the degradation of hydrocarbons in China (Lan et al. 2011b; Liu et al. 2010).

  • Methanomethylovorans hollandica-related sequences were the most abundant Archaea detected in bioreactors treating high-level antibiotic (mainly streptomycin) wastewater in China (Deng et al. 2012).

  • Methanosarcinales amounted to 1 % of the anoxic sediments underlying cyanobacterial mats of hypersaline (15–20 % salinity) ponds in a Mediterranean saltern in the south of France (Mouné et al. 2003).

  • Analysis of mcrA gene libraries from the hypersaline athalassohaline Tirez Lagoon in Spain yielded Methanohalobium and Methanolobus sequences most abundantly in the dry season, when methanogenesis is mainly based on the degradation of methylated compounds (Lozada-Chávez et al. 2009).

  • The stratified hypersaline (7–7.5 % salt) microbial mats in the Guerrero Negro, Baja California, Mexico lagoon, where methylated amines are the main methanogenic substrates, have a methanogen community that consists exclusively of Methanosarcinales, as monitored by mcrA gene amplification and sequencing. A pronounced vertical stratification was observed, with Methanolobus in the photic zone, Methanohalophilus in the middle, and Methanococcoides in the sediment below the mat (Jahnke et al. 2008; Orphan et al. 2008).

  • The deep hypersaline L’Atalante brine on the bottom of the Mediterranean Sea yielded Methanohalophilus sequences from the deeper part of the halocline and from the hypersaline brine. mRNA coding for Methanohalophilus methyl-CoM reductase was detected as well in the community sampled (Hallsworth et al. 2007; McGenity 2010).

Pathogenicity, Clinical Relevance

Methanosarcina and Methanimicrococcus spp. have occasionally been detected in the rumen of cows and sheep (Jarvis et al. 2000; Kong et al. 2013), and Methanosarcina sp. was isolated from the human periodontal pocket (Robichaux et al. 2003). But no members of the Methanosarcinaceae are known to be pathogenic or otherwise harmful to humans, to animals, and to plants.

Application

Methanosarcina spp. and other members of the family Methanosarcinaceae are important components of the microbial community in anaerobic digestors for the breakdown of different types of organic wastes. Together with members of the genus Methanothrix (family Methanotrichaceae), they convert acetate to methane and carbon dioxide, a process not performed by any other known groups of methanogens. Methanosarcina is well suited for biogas formation: it is a robust organism, it tolerates to high concentrations of acetate and of ammonia, it can survive large fluctuations in pH, and it also tolerates salt (De Vrieze et al. 2012). But no cases were reported in which cultures of members of the Methanosarcinaceae were added as an inoculum to promote anaerobic digestion processes.