Methanogens: Definition and Classification

Marco Antonio Hernandez Cardona, Julie Zundel
  • Author
    Marco Antonio Hernandez Cardona

    Marco has taught elementary school, high school and college (math, physics, chemistry, ecology, calculus, and other science subjects) for over 3 years. He is a civil engineer with a MEng degree on Environmental Engineering in the Yucatan Autonomous University (UADY) in Mérida, México

  • Instructor
    Julie Zundel

    Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

In this lesson, learn what methanogens are. Understand the domain Archaea to which methanogens belong. See where methanogens live and find examples of methanogens. Updated: 12/01/2021

Table of Contents


What are Methanogens?

Methanogens are organisms that produce methane as a metabolic by-product under anoxic conditions. They are classified as archaea, a distinct domain of bacteria, and are found in cow stomachs, swamp mud, and other environments where there is no oxygen.

For these organisms, methane is a waste product of their energy production process. Methane is a gas that plays a special role in the Global Warming phenomenon so it is of special interest to mankind. Currently, more than 70% of the emissions of this gas come from the activity of methanogens. Also, methane and other biogases are of special interest to be collected and used as fuel, so it represents an alternative to generate energy and eliminate its potential as a pollutant. That's why studying methanogens and their processes are very important.

Methanogens are found in a wide variety of anaerobic environments (with the absence of oxygen). These include marine and freshwater sediments, biodigesters, hot springs, ruminant digestive tracts (like cows or goats), termites, and human beings. This distribution, however, is dependent on factors such as the availability of substrate(food for methanogens), temperature, pH, and salinity, as well as the abundance of final electron acceptors, such as nitrates and sulfates among others, whose reductions are more favorable than that of carbon dioxide as methane.

Methanogens Domain

The current classification of living things (in force since 1977) includes three domains and seven kingdoms. The domains group living beings by their cellular characteristics. The kingdoms group them by their evolutionary kinship. The classification system for living beings is structured as follows:

  • Eukarya Domain: contains five kingdoms, which are Animalia, Plantae, Fungi, Protozoa, and Chromist.
  • Bacteria Domain: contains the bacteria kingdom.
  • Archaea Domain: contains the kingdom archaea.

The methanogens belong to the Archaea domain. It encompasses unicellular prokaryotic organisms without a differentiated nucleus, as well as bacteria. However, they are living beings with genetic and metabolic characteristics that are closer to eukaryotic organisms, although their evolutionary path is completely different. They can be present in the water of the oceans, in different types of soil, and even in the human digestive tract.

The organisms that belong to the Archaea domain share characteristics like:

  • They have a very wide nutritional variety: they feed on hydrogen, sugars, or ammonia.
  • They can use carbon or sunlight for energy.
  • They reproduce asexually, after duplicating their DNA.
  • They have cell walls like organisms of the Eukarya and bacteria domains but are made of other materials.

Some archaea, like methanogens, are extremophiles. That means that they tolerate and resist extreme conditions like extreme pH (very acidic or very alkaline conditions), extreme salt concentrations, extreme radiation conditions, high pressures, lack of humidity, and high or low temperatures. Also, methanogens are obligate anaerobes which means that they don't need oxygen to grow and reproduce and they have high nutritional requirements. The process of obtaining energy from these organisms is called methanogenesis and is a process that all methanogens share. In this process, methanogens consume carbon dioxide and hydrogen and produce methane.

In most of their habitats, methanogens are associated with various groups of bacteria to carry out the degradation of matter organic, where methane formation represents the last step of this process. An example of this is hydrogen-producing bacteria. This is called syntrophy, the process where one organism lives off of what another organism releases.

Methanogens Classification

Methanogens are classified into 5 different orders. What they have in common is that they all produce methane, and all are obligate anaerobes. This classification is based upon their differences in physiological properties, the substrates they need to do the methanogenesis, diet, their form, the way they move, and cell structure:

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  • 0:01 Definition of Methanogens
  • 1:07 Classification &…
  • 3:39 Example Methanogens
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Frequently Asked Questions

What do you mean by methanogens?

Methanogens are extremophile and obligate anaerobe organisms that belong to the Archaea domain and produce methane by the methanogenesis process in anoxic conditions, using substrates like carbon dioxide or hydrogen,

Where are methanogens found?

hey, can be found in places with anoxic conditions like anoxic sediments, animal digestive tracts, underwater hydrothermal vents, and wastewater treatment plant sludges.

What do methanogens do?

Methanogens, under anoxic conditions take substrates like carbon dioxide, hydrogen, and organic matter to produce methane by the methanogenesis process. This methane can be collected and used as fuel.

How do methanogens survive?

Methanogens can survive under extreme conditions like high or low temperatures, high pressures, high salinity. They take compounds that other organisms release and under anoxic conditions, they release methane. That is the way they produce their energy.

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