DESCRIPTION OF THE PHYLUM METHANOBACTERIA (BOONE 2001)
| ARCHAEA> EURYARCHAEOTA> METHANOBACTERIA |
PHYLUM METHANOBACTERIA LINKS
| Methanobacteria (me-tha-no-bak-TE-re-a) is derived from two words that mean “methane” (New Latin: methanum derived from an ancient Greek word for wine) and “little stick” (bakterion -βακτήριον). The name is a reference to the generation of methane by these organisms. |
| INTRODUCTION TO THE METHANOBACTERIA The Methanobacteria may be among the most abundant organisms on earth (Figures 1 and 2). They occur in sediments or any other substrate low in oxygen and with enough water to support them. In such environments they reduce carbon dioxide with hydrogen, formate, acetate, or methanol (Margulis and Schwartz 1998) and release methane as a waste product. Methanogens are the sources of methane bubbles known as marsh gas common to wetlands and anoxic lake sediments. Also, they occur as commensals in the guts of animals such as termites and cows. All in all, methanogens likely are the primary contributors to atmospheric methane, a very powerful greenhouse gas. This phylum almost certainly is paraphyletic since all of these organisms are lumped together based only on the ability to generate methane by the reduction of carbon dioxide (e.g. Gao and Gupta 2007). Garrity et al. (2001 and 2003) separate the methanogenic taxa into three groups that they refer to as classes within their phylum Euryarcheota. Margulis and Schwartz (1998) also define the Methanobacteria as a group within their phylum Euryarcheota which also includes the halobacteria. We have kept them as a separate group, but only provisionally, until more work can clarify their relationships. We do believe, however, that the differences in physiology between the extreme halophiles and the methanobacteria warrant placing them into separate phyla (see Figure 3). |
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| FIGURE 1. Two genera of methanogenic bacteria: Methanosarcina
(cocci)
(text with tooltip)
tipso
and Methanosaeta (Methanothrix?,
rods
(text with tooltip)
A rod is an elongate cell form such that it has distinct ends (called poles).
). Image from http://www5.gtz.de/gate/techinfo/biogas/basics/microbiol.html | FIGURE 2. SEM micrograph of Methanococcus. Image by Tashiror from MicrobeWiki |
FIGURE 3. The relative position of the classes within the Methanobacteria in the context of the other phyla in the Euryarchaeota. They occupy a clade called Neobacteria, which also includes the Halobacteria, both of which have growth maxima at non-extreme temperatures.
C = CRENARCHAEOTA
E = EURYARCHAEOTA
Eu = EURYTHERMEA CLADE
Ne = NEOBACTERIA
| FURTHER READING: DISCOVERY OF THE DOMAINS OF LIFE |
| LITERATURE CITED Black, J. G. 2002. Microbiology, Principles and Explorations. 5th ed. John Wiley and Sons, Inc. New York. Boone, D. R. 2001. Class I. Methanobacteria class. nov. In: D. R. Boone and R. W. Castenholz, eds. Bergey’s Manual of Systematic Bacteriology Volume 1: The Archaea and the deeply branching and phototrophic Bacteria. 2nd ed. New York: Springer Verlag. pp. 169. Gao, B. and R. S. Gupta. 2007. Phylogenetic analysis of proteins that are distinctive of Archaea and its main subgroups and the origin of methanogenesis. BMC Genomics. 8:86. http://www.biomedcentral.com/1471-2164/8/86. Garrity, G. M., M. Winters, and D. Searles. 2001. Bergey’s manual of systematic bacteriology. 2nd ed. Springer-Verlag. New York. Garrity, G. M., J. A. Bell, and T. G. Lilburn. 2003. Taxonomic Outline of the Prokaryotes. Bergey’s Manual of Systematic Bacteriology. 2nd edition. Release 4.0. Springer-Verlag. New York. pp. 1-397. Margulis, L. and K. Schwartz. 1988. Five kingdoms, an illustrated guide to the phyla of life on earth. 2nd Edition. W. H. Freeman and Co. New York. Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Co. New York. Woese, C. R. and G. E. Fox. 1977. Phylogenetic structure of the prokaryotic domain: the primary kingdoms. Proceedings of the National Academy of Sciences USA. 74:5088-5090. Woese, C. R., O. Kandler, and M. L. Wheelis. 1990. Towards a natural system of organisms: Proposal for the domains Archaea, Bacteria, and Eucarya. Proc. Natl. Acad. Sci. USA. 87: 4576-4579. |
| By Jack R. Holt. Last revised: 02/05/2013 |
