Methanogens: Definition, Classification & Examples

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  • 0:01 Definition of Methanogens
  • 1:07 Classification &…
  • 3:39 Example Methanogens
  • 4:51 Lesson Summary
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Lesson Transcript
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.

Tiny organisms that can die if they are exposed to oxygen? Sounds strange, but it's just an ordinary day for a methanogen. This lesson will explore methanogens, describing their distinguishing characteristics and then giving some examples.

Definition of Methanogens

If you could live anywhere, what city would you choose? Perhaps you would choose a tropical city so you could enjoy the sun and beautiful aquamarine water. Or a city surrounded by snowy mountains so you could ski and enjoy the majestic scenery. Or inside of a cow's gut where you could happily produce gases, resulting in lots of cow burps. Wait, what?

It sounds crazy but some organisms, like methanogens, live and thrive in peculiar and hostile environments, like a cow's gut. These are microscopic organisms that produce methane as a byproduct of their metabolism. Methanogens belong to a group of organisms called archaea (more on that later) and are obligate anaerobes, or organisms that live without oxygen. Methanogens belong to a fascinating group of organisms known as extremophiles, or organisms that live in extreme conditions. Let's explore these extremophiles in more detail.

Methane gas is composed of one carbon atom and four hydrogen atoms

Classification and Characteristics of Methanogens

Methanogens belong to the archaea domain, which is one of three domains. The other two domains are bacteria and eukaryota (this is where you belong). Not so long ago, archaea were thought to be bacteria, but they are actually quite different (about as different as you are from bacteria)! It's a little confusing because archaea sometimes get called by their original name, archaebacteria. Just realize archaea is the updated name, but the term 'archaebacteria' gets thrown around from time to time.

The three domains of life: archaea, which includes the methanogens, is one of the domains
Three domains of life

Organisms, like methanogens, in the archaea domain are extremophiles. For example, some archaea live in really hot temperatures, under really high pressures or in really salty environments. Methanogens are no exception, living in the guts of cows, deep in swamps, and even in the muck from sewage treatment plants.

Methanogens are considered one of the most diverse groups in the archaea domain, with over 50 species, each with its own unique characteristics. Fortunately, they all have a few things in common.

  • They are obligate anaerobes, so they live in places without oxygen. Oxygen actually harms them and sometimes kills them.
  • Most have a cell wall, which offers the cell support, and a rigid structure that protects them. Plants, bacteria and fungi all have cell walls, too, but archaea have cell walls made from a different material.
  • They come in two shapes: coccus (plural cocci), which is a circle-shape, and bacillus (plural bacilli), which is a rod-shape.
  • Most consume carbon dioxide and hydrogen and release methane gas.
  • All undergo methanogenesis, or the formation of methane by microbes.
  • They depend upon syntrophy, or when one organism lives off of the products of another organism. Most methanogens live closely with certain bacteria that produce molecules that the methanogens can consume.

There are five main orders of methanogens, each having certain characteristics, such as: different shapes, different habitats, different genetic makeup, different diet (although they all produce methane, some consume different gases), and different ways in which they move (or cannot move). Although they are all obligate anaerobes, some can survive in high salt concentrations, basic conditions, acidic conditions, cold conditions and extreme temperatures.

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