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Sunday, July 26, 2009


Written by: Tan Kiat Yi

Bacteria are vulnerable to damage from adverse environmental factors such as heat. So, there are a few types of bacteria that have a special trick up their “sleeve” that allows them to be dormant when the need arises. This “trick” is the ability to form resistant resting structures called endospores.

What they do
An endospore, as its name suggests, “endo” meaning “inside” and “spore” meaning “a resistant body”, is an internal structure formed by the bacterium that makes the bacteria dormant and tough. It ensures the survival of a bacterium through periods of environmental stress. Some examples of environments that endospores are capable of resisting are shown in the diagram below.
When the bacterium is put in favorable conditions again, it will revert to its vegetative state through germination, where it would carry out normal cell functions again. However, activation must take place first, it may be triggered by heating the endospore.

How they are formed

Endospores are formed through the process of sporulation. Under adverse environmental conditions, DNA replicates and a cytoplasmic membrane septum forms at one end of the cell. Another membrane then forms around one DNA molecule, and a forespore is formed. Then, the membrane layers synthesize peptidoglycan in the space between them to form the first protective coat, the cortex. A spore coat composed of a keratin-like protein then forms around the cortex. In some cases, an outer membrane made up of lipid and protein called an exosporium is seen. Finally, the remainder of the bacterium is degraded and the endospore is released. Sporulation usually takes around 15 hours.

Process of formation of endospore

Structure of endospore

In short, an endospore is an internal structure formed when the bacterium produces a thick internal wall that encloses its DNA and part of its cytoplasm.

Endospore forming bacteria
Not all bacteria can create endospores, only gram-positive bacteria can do so; some examples of endospore creating bacteria are the genus Bacillus, the genus Clostridium, and several other genera of bacteria including Desulfotomaculum, Sporosarcina, Sporolactobacillus, Oscillospira, and Thermoactinomyces. You can read more about gram-positive bacteria here.

Endospores can be seen under the light microscope using only special staining techniques such as the Moeller stain and Schaeffer-Fulton stain, as its walls are impermeable to most dyes and stains.

Endospores stained green

Danger to Humans
Despite the few groups of endospore forming bacteria, people do usually come in contact with them. These bacteria can commonly be found in soil and water. Thankfully, most of these bacteria are harmless, and pose no threat to humans.
However, there are some important endospore producers that can cause serious infectious disease. Here are some brief examples of the above:

· Bacillus anthracis - the causative agent of anthrax

· Clostridium tetani - the agent of tetanus

· C. perfringens – may cause gas gangrene.

· C. botulinum – may cause botulism

· C. diff. – resistant to antibiotics


Vaccinations and antibiotics are used to prevent and treat infections caused by endospore bacteria. However, these may prove pointless if the infection resides deep in the tissue. Also, even though endospores are resistant to extreme heat and radiation, they can be destroyed by burning or autoclaving, a process used to sterilize things. Exposure to extreme heat for an extended period of time, prolonged exposure to high energy radiation, such as x-rays and gamma rays would also affect

While resistant to extreme heat and radiation, endospores can be destroyed by burning or autoclaving. Exposure to extreme heat for a long enough period will generally have some effect, though many endospores can survive hours of boiling or cooking. Prolonged exposure to high energy radiation, such as x-rays and gamma rays, will also kill most endospores.

So there you have it, all you need to know about endospores. I hope that you've learned more about these amazing bacterial structures!

Here are some reference links: