Spirochetes Meaning

Spirochete is also spelt as spirochaete, which refers to any of a group of spiral-shaped bacteria. Some of them are serious pathogens for humans, that cause diseases like syphilis, yaws, Lyme disease, and also relapsing fever. Examples of spirochetes are Spirochaeta, Treponema, Borrelia, and Leptospira.

What is Spirochete?

Spirochetes are gram-negative, motile, and spiral bacteria. Their length is from 3 to 500 m long. Spirochetes are very different and they have endocellular flagella also known as axial fibrils, or axial filaments, which is between 2 and more than 100 per organism, depending upon the species. 

Each axial fibril of spirochetes attaches at an opposite end and then winds around the cell body that is enclosed by an envelope. Spirochetes are characteristically found in a liquid environment such as in mud and water, blood, and lymph.

Spirochetes Classification

  • Domain - Bacteria: 

A large group of single-celled prokaryotes that lacks membrane-bound organelles found in just about any environment across the world that are soil, water, air, hot streams, etc. They may exist as parasites, or as free-living organisms, or even as symbionts with some of the species being very beneficial to man. 

  • Phylum - Spirochaetes: 

Bacterial cells that are characterized by a unique diderm (double-membrane) which gives them their gram-negative characteristic. They are usually thin with a spiral-shaped appearance and also possess flagella which are commonly known as axial filaments.

  • Order - Spirochaetales: 

These helically shaped bacteria have the capability of locomotion. They display significant variation in their physiology and also in their distribution. 

In nature, they might exist as facultative anaerobes, obligate anaerobes, or obligate aerobes. This order is further divided into three major phylogenetic families that include Spirochaetaceae, Brachyspiraceae, and Leptospiraceae.

Ecology and Distribution

As a group of bacteria, the spirochetes are distributed in nature. They can be found in different environments across the whole world. Many of the species on this planet have shown to exist as free-living organisms and also can be found in different habitats in water such as surface water or freshwater, or in lakes, salt marsh sediments, or even in mud, sediments, and also deep-sea vents among others.

Apart from the species found in these habitats, the other species form an association with various hosts that are termites, protozoa, mammals, etc., and are hence found living within these hosts such as in the intestine. While some of the species are also very beneficial, whereas some are pathogenic and they tend to cause diseases such as Lyme disease, dysentery, etc. 

Because of the diversity between species and also where they are found in nature, the spirochetes are classified based on their distribution.  Obligatory Aerobic Spirochetes that need oxygen for metabolism might be found in water and sometimes also in the soil as free-living organisms with some species living as pathogens in their hosts.

Members of the genus Leptospira have been classified as Obligatory Aerobic Spirochetes. The Anaerobic and the facultative anaerobic spirochetes exist as free-living forms and also include members of the genus Spirochaeta. They are usually found in various environments where they can survive on a variety of organic matter like disaccharides, pentoses, and hexoses, etc.

Some of the other habitats in which spirochetes can be found are in High salinity ponds or hot/boiling water springs.

FAQs (Frequently Asked Questions)

Q1. Write a Short Note on the Cell Structure and Morphology of Spirochetes.

Ans: As the name suggests, the spirochetes have a spiral morphology that is used to classify them based on their morphology. From the early records, it is believed that spirochetes were first observed under the microscope. It was first observed by Van Leeuwenhoek, who noted that while they are in motion, they "bent their body into curves in going forwards". Today, it is understood that this morphology is the result of flexible peptidoglycan cell wall wounds by several axial fibrils. 


Along with the cell wall, these fibrils are in turn covered by an outer membrane just similar to the membrane found in the Gram-negative bacteria. The axial fibril, which has a very similar structure to the flagellum that is found in bacteria, always consists of a shaft and also a covering sheath. It is also made up of an insertion apparatus that differentiate into a terminal knob.


Depending on the species, the shaft has either a filamentous or a globular substructure. While it also has similarities to the shaft found in bacterial flagella. It is located between the inner and the outer membranes that are within the periplasmic space and along the length of the organism.  


The shaft that is a filament of the axial fibril is covered by a sheath. When the sheath is removed, the internal core approximately comes in a range between 10 and 16nm in diameter. Apart from giving the organism its shape, the axial fibrils have been shown to contribute to the movement of spirochetes through a twisting motion. 


The axial filaments or fibrils are also very commonly known as the endocellular flagella in spirochetes.

Q2. Write a Short Note on the Outer Structural Features of Spirochetes.

Ans: Like several other bacteria found on this planet, the cell body of spirochetes is enclosed within several layers. These include the outer and the inner membrane, the peptidoglycan layer, and also the cytoplasmic membrane.


Some of the species like the Treponema pallidum have been shown to contain a slime layer covering the cell. In these species, the layer is associated with serological non-reactivity. All the species have an outer membrane or known as the envelope that surrounds the entire cell. This is particularly crucial for the survival of the cell. The damage to this membrane results in a loss of intracellular components and also the consequent death of the cell.


This membrane is especially fragile to the various adverse conditions during the stages of cell development. When exposed to hypertonic conditions, the outer membrane or the envelope of Leptospira bacteria separates from the protoplasmic cylinder producing a spherical shape. 


Unlike the other cell membranes, the outer membrane of spirochetes does not contain a phospholipid bilayer. According to several studies done by the researchers, lipids make up about twenty percent of the total dry weight. This layer also consists of several proteins that include lipoproteins and also B-barrel proteins.