Spirochetes: Definition & Characteristics

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  • 0:00 Prokaryotes vs. Eukaryotes
  • 1:02 Spirochetes and Endoflagella
  • 1:52 Where are Spirochetes Found?
  • 2:36 Mutualism
  • 3:04 Parasitism
  • 5:23 Lesson Summary
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Lesson Transcript
Instructor: Erika Steele

Erika has taught college Biology, Microbiology, and Environmental Science. She has a PhD in Science Education.

Spirochetes are a type of bacteria. Bacteria are prokaryotic cells; a kind of cell that does not have a nucleus or other organelles. They are found everywhere and come in many shapes. This lesson will focus on the definition and characteristics of this tiny bacteria and how it may affect humans.

Prokayotes Vs Eukaryotes

All living things are made up of one or more types of cells. These cells can be prokaryotes or eukaryotes. Prokaryotic cells lack a nucleus and organelles. Organelles are a specific structure within a cell. Eukaryotic cells have a nucleus and various organelles.

Bacteria are microorganisms made up of prokaryotic cells. Therefore, spirochetes and other bacteria such as Bacillus anthracis, the causative agent of anthrax, are prokaryotic cells. Like eukaryotic cells, prokaryotic cells are diverse in morphology and behavior. One of the ways bacteria can be identified is based on cell shape. They are:

  • Coccus: spherical
  • Bacillus: rod-shaped
  • Vibrio: comma-shaped
  • Spirillum: spiral-shaped
  • Spirochete: cork screw shaped

Spirochetes and Endoflagella

Microscopically, spirochete- and spirillum-shaped bacteria can look similar, but they can be distinguished based on the type of flagella present. Flagella are cell structures that allow for movement.

The spirochetes have a type of flagella called endoflagella. These are bundled together to form an axial filament. The axial filaments wrap around the cell body, connect both ends of the cell, and embed in the outer membrane. Spirilla-shaped bacteria do not have endoflagella; their flagella are external and only connected to one end of the cell.

The attachment of the endoflagella to the cell causes spirochetes to rotate as they move through the environment. Other bacteria, including spririllum, do not rotate as they move.

Where Are Spirochetes Found?

Spirochetes are found free-living in the environment or in association with a host. Spirochetes account for a large amount of biodiversity in soil or aquatic ecosystems, but they are rarely cultivated. This may be because they are small, even for bacteria. They are often missed in environmental samples because their width or diameter, between 0.1-0.6 µm, is below what can be resolved by a conventional light microscope. Spirochetes are also very difficult to cultivate in the lab; many of them will only grow when in association with a host organism and only exist as symbionts. A symbiont is an organism that lives inside another organism or in symbiosis with another organism.


Some spirochetes found associated with a host are beneficial or completely harmless to the host. Many termites have symbiotic spirochetes living in their guts and are an example of mutualism. Mixotricha paradoxa is a type of protozoan found in a species of Australian termites. This protozoan uses spirochetes for movement. Other spirochetes found in the guts of termites are involved in digesting plant materials for the termite host.


Many spirochetes that associate with a host are parasites that cause diseases. There are three families of spirochetes, two of them containing species that cause human disease.

The Spirochaetaceae contains the genera Treponema and Borellia.

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