Higher order taxa:
Archaea; Euryarchaeota; Methanobacteria; Methanobacteriales; Methanobacteriaceae
Description and Significance
Methanosphaera stadtmanae is a Gram-positive, non-motile archaeon that obtains energy for growth by using hydrogen to reduce methanol to methane. This is a unique characteristic for a member of the Methanobacteriales, because it is usually restricted to members of the Methanosarcinales. Also, it is important to note that the archaeon can neither oxidize methanol to CO2 nor reduce CO2 to methane and that it is incapable of growing on CO2. Instead, it requires both acetate and CO2 as main carbon sources. Further, M. stadtmanae is the first human archaeal commensal whose genome has been sequenced.
The circular chromosome of Methanosphaera stadtmanae is 1,767,403 Bp in length. It contains only 1,534 protein-encoding sequences (CDS) and its G + C content is 28%, both of which are the lowest among all methanogens and among all archaeal gemones sequences so far, respectively. Also, it is noteworthy that 30-bp sequence is repeated 59 times in a 4.8 kbp genome segment. The genome of M. stadtmanae lacks 37 CDS present in the genomes of all other [../methanogens/methanogens.html methanogens], which includes the genetic information for the synthesis of molybdopterin (required for the enzyme catalyzing the first step of methanogenesis from CO2 + H2) and for carbon monoxide dehydrogenase/acetyl-coenzyme A synthase complex. This explains why the archaeon is unable to reduce CO2 to methane or to oxidize methanol to CO2 and why it requires acetate for growth.
Cell Structure and Metabolism
Methanosphaera is spherical-shaped. It produces methane by reducing methanol using methanol and hyrogen only. Also, 95% of the cell carbon is synthesized from acetate and carbon dioxide. Since neither CO2 nor acetate is utilized to produce methane, most of the CO2 or enriched acetate will go into the cell components. This characteristic maximizes the possibility to follow the often unique biosynthetic pathways of Methanogens. Also, it appears to be auxotrophic for isoleucine or leucine and for thiamine.
CH3OH + HS-CoM → CH3-S-CoM + H2O
(Δ G°' = -27 kJ/mol)
CH3-S-CoM + HS-CoB → CH4 + CoM-S-S-CoB
(Δ G°' = -30 kJ/mol)
CoM-S-S-CoB + 2e- + 2H+ → HS-CoM + HS-CoB
(Δ G°' = -55 kJ/mol)
H2 → 2e- + 2H+
(Δ G°' = 0 kJ/mol)
ADP + Pi → ATP + H2O
(Δ G°' = -32 kJ/mol)
The archaeon is known to live in human large intestine. It is responsible for production of methane gas by humans.
Shelton Bank, Bin Yan, and Terry L. Miller. "Solid C CPMAS NMR spectroscopy studies of biosynthesis in whole cells of Methanosphaera stadtmanae" Solid State Nuclear Magnetic Resonance 7 (1996) 253-261.
Wolfgang F. Fricke, Henning Seedorf, Anke Henne, Markus Kruer, Heiko Liesegang, Reiner Hedderich, Gerhard Gottschalk, and Rudolf K. Thauer. "The Genome Sequence of Methanosphaera stadtmanae Reveals Why This Human Intestinal Archaeon Is Restricted to Methanol and H2 for Methane Formation and ATP Synthesis" Journal of Bacteriology, January, 2006, Vol. 188, No. 2, p. 642-658.
Vazoller, R.F.; Manfio, G.P., and Canhos, V.P. "Diversidade no Domínio Archaea." In Canhos, V.P. and Vazoller, R.F. (eds), Microrganismos & Virus, Volum 1 Serie Biodiversidade do Estado de São Paulo: síntese do conhecimento ao final do século XX Org. by Joly, C.A. and Bicudo, C.E.M., Editora WinnerGraph & FAPESP, São Paulo, (1999) p. 118.