BIOL/CSES 4684

Methanobacterium

SOIL MICROBIOLOGY

This webpage was created by James Whiticar

1. IDENTIFYING CHARACTERISTICS

Strictly anaerobic.
Straight or slightly curved rods, but not helical.
0.2 ? 1.0um x 1.2 ? 120 um in size.
Cells stain Gram negative.
The percent G + C ranges from 35 to 70%.
Chemoautotrpohs.
Substrates for energy are mostly H2 and/or formate.
Cell envelope compostion is mostly pseudomurein.
Optimum temperature ranges from 35 ? 70OC.
Optimum pH ranges from 6.0 ? 8.5.
Habitat contains low NaCl concentrations.
All use ammonium, sulfide, and elemental sulfur.
Nonmotile.
Endospores are not present.
Founded in flooded soils.

The above picture shows M. thermoautotrophicum under phase contrast microscopy (1,000X).

2. TAXONOMIC DESCRIPTION
The species within the genusMethanobacterium vary widely in length and filaments are common. Cell walls appear to be Gram positive, but are composed of pseudomurein rather than peptidoglycan. They are non-motile and flagella are absent. Metabolism is strictly anaerobic and H₂ and/or formate are used as an electron donor. All species grow with H₂ and CO₂ as a substrate for methanogenesis. Cells are mesophillic or thermophillic. All species fail to grow under aerobic conditions and most are acid tolerant (will grow at pH less than 5). Methylamines, methyl sulfides, acetates, are not catabolized. They can use sulfur, sulfite, thiosulfate, or ammonium sulfide as sulfur sources and glutamine, ammonium, or urea as nitrogen sources. There are 12 species of genus Methanobacterium and they have been isolated from aneraobic digestors, sewage sludge, manure, groundwater, and formation water of oil-bearing rocks.

The above picture shows M. thermoautotrophicum under electron microscopy (100,000X).

3. ISOLATION AND ECOLOGY
There are several media available for the isolation of methanobacteria. Most of the media consist of yeast extract in combination with compounds such as xylose, tryptone, and glucose. Also, antibiotics in conjunction with enrichment techniques can be useful as selective agents in isolating methanobacteria. However, methanobacteria must be present in the soil in order for successful isolation to occur.

Methanobacterium is commonly found in alkaline flooded soils, sediments, and other anoxic environments where inorganic electron acceptors such as sulfate, iron hydroxides, and nitrate are limiting. Methanobacteria have numerous applications, especially in the degradation of wastes rich in organic matter to methane and carbon dioxide and treatment of domestic sewage (see CARBON CYCLE). The literature on degradation of organic compounds by methanobacteria will grow rapidly as the usefulness of this microbe in bioremediation is more widely recognized.

4. ADDITIONAL SOURCES AND INFORMATION
Atlas, R.M. 1993. Handbook of Microbiological Media. CRC Press. Boca Rotan, Fl. pp. 575.

Balows, A., M. Dwarkin, W. Harder, K.H. Schleifer, and H.G. Truper. 1988. The Prokaryotes: A Handbook on the Biology of Bacteria: Ecophysiology, Isolation, Identification, Application. Springer-Verlag. London. pp. 731-733.

Boone, D.R., W.B. Whitman, and P. Rouviere. 1993. Diversity and Taxonomy of Methanogens. Chapman & Hill, New York.

5. LINKS TO OTHER SITES ON METHANOBACTERIUM
Oregon Collection of Methanogens. 1995. Methanobacterium. University of Oregon Web Site. This site contains access to information about Methanobacterium and other methanogens.