Endospore: Definition, Formation & Structure

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  • 0:00 Endospores
  • 1:04 Endospore Formation
  • 2:29 Endospore Structure
  • 3:54 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.

When the going gets tough, the tough get endospores. Special bacteria are able to produce endospores, which allow them to survive in conditions that would normally kill them. This lesson defines endospore and then examines the structure and function of it.


Imagine you're having a bad year. You lost your job. Your significant other left you. Your dog ran away, and your car was stolen. Wouldn't it be nice if you could just take a break for a while and start over when conditions became favorable? If you were a bacterium, you could do just that! Specifically, a group of bacteria that produce endospores.

Obviously, bacteria don't suffer the same way as people, but being a bacterium isn't always great. So when life gets hard, certain bacteria use endospores to 'take a break.' Endospores are dormant, tough structures made by some bacteria, such as Bacillus. These structures allow the bacteria to survive unfavorable conditions, such as intense heat, disinfectants, and even UV radiation. Sure, a trip to a tropical island sounds like a better way to take a break to you and me, but endospores are an adaptation that have allowed bacteria to survive conditions that would otherwise be disastrous for them.

Endospore Formation

Let's look at how endospores form. Imagine that a particular bacterium suddenly finds itself in an unfavorable environment and the temperature is getting too hot. Here are the six steps that would occur if the bacterium formed an endospore:

Step 1: The bacterium copies its DNA. This is important because all of the information the bacterium needs is in the DNA. A wall then forms, separating the two copies of DNA inside the mother, or starting, cell.

Step 2: The wall encircles the DNA completely, creating a cell within a cell. the new cell inside of the mother cell is called a forespore.


Step 3: Peptidoglycan, or a substance made up of sugars and amino acids, acts like a mesh and surrounds the outside of the forespore. This cell layer structure is now called the cortex.


Step 4: Water is removed from the forespore.

Step 5: Outside of the cortex, yet another layer is added, but this time it's a protein coat called a spore coat. In some bacterium, there's even another layer added after the spore coat!

Step 6: The mother cell is destroyed, and the endospore bursts out.

When conditions become favorable again, the endospore germinates, or resumes metabolic function, thus ending the dormant, endospore stage.

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