Bacterial Endospores | Definition, Development & Function
What is an example of a bacterial spore?
An example of a bacterial spore is an endospore. This spore is highly resistant to heat, desiccation, radiation, chemicals, and some disinfectants.
How are bacterial spores formed?
Bacterial spore formation is triggered once nutrients such as carbon and nitrogen become deficient. The formation of the spores takes several hours, and it occurs in a seven-stage process. The process starts with forming an axial chromatin filament and ends with the formation of a mature endospore inside the mother cell.
What is a bacterial endospore?
A bacteria endospore is a type of spore that is formed within a vegetative or mother cell. The vegetative cell is mainly referred to as a sporangium.
What is the function of bacterial endospores?
The primary function of a bacterial endospore is to ensure the survival of a bacteria during harsh environmental conditions. These could be overpopulation, nutrient deficiency, or unfavorable climatic conditions.
Recommended lessons and courses for you
Bacteria are one of the oldest microbes on Earth. They are believed to have existed more than 3.5 billion years ago. These microorganisms are said to have initiated life on Earth after being carried from other planets by meteorites. In 1915, Dr. Charles Walcott discovered bacteria fossilized in rocks. The ancient bacteria were harmless, and they were attributed to rocks formation where they were drawing calcium from the seawater. In addition, other researchers have been able to discover a Bacillus strain from the earth salt. This Bacillus strain is said to be more than 250 million years old. It is believed that the bacterial cells of this strain were trapped between salt crystals during the Permian era.
Ancient bacteria were known to infect protozoan predators, such as amoeba, before they evolved and started causing diseases in humans. These bacteria cells and their DNA can survive in sediments, soil, and salts in their dormant state. During this period, the rate of DNA destruction is significantly reduced. In addition, bacteria such as Clostridium and Bacillus produce endospores capable of surviving external conditions for many years.
Some species of bacteria produce spores when faced with adverse environmental conditions such as nutrient deficiency and overpopulation. These spores ensure the survival of bacteria and they are not easily affected by heat, radiation, chemical disinfectants, or desiccation. Bacterial spores are formed within bacteria vegetative cells; thus, they are referred to as endospores. The vegetative cells are commonly referred to as sporangia, and the process involved in the formation of these spores is known as sporulation. The bacteria spores may remain within the vegetative cell until favorable conditions prevail for the germination; or they may be released by digesting the cell wall of the vegetative or mother cell.
 |
Endospores are spores that are formed within the cells, mostly in bacteria. The formation of endospores in bacteria ensures their survival. They are quite different from the spores formed in fungi or plants that are meant for reproduction.
Endospores are capable of surviving for many years while still preserving the genetic material of bacteria. Once the conditions are favorable, these spores get reactivated and germinate. The most common bacteria that form endospores are Bacillus and Clostridium species.
Once an endospore matures, it appears as a round cell within the vegetative or the mother cell. Their position inside the mother cell varies from one bacterium to the other. They may either be positioned at the center, terminal or subterminal. In some bacteria species, the endospore may remain within the mother cell until their germination. Other bacteria produce the enzyme autolysin, which digests the mother cell wall, liberating the endospores.
Endospores Structure
A bacteria endospore comprises an outer covering that is thin and delicate, referred to as an exosporium. Under the exosporium is a thick spore coat that is made of layers of proteins. The spore coat is impermeable, and thus it is responsible for the chemical resistance trait in endospores. In addition, the spore coat contains enzymes that are necessary for endospore germination.
Beneath the spore coat is the cortex that is made up of the spore peptidoglycan. The spore cell wall is located in this region (the cortex). The spore cell wall surrounds the spore protoplast. The spore protoplast consists of the ribosomes, nucleus, and energy-generating machinery, though inactive.
 |
The endospore development occurs in several stages. Depending on the bacteria species, this process may take several hours. For instance, some Bacillus species require 10 hours to form endospores. A vegetative cell usually has two chromosomes, and endospore development occurs in seven stages.
Stage 1 — Formation of an axial filament of the nuclear material.
Stage 2 — Formation of the forespore septum. This is formed by the inward folding of the cell membrane of the mother cell, thus enclosing some portion of DNA. This divides the nuclear material into two compartments.
Stage 3 — Engulfment of the immature endospore by a second membrane.
Stage 4 — Formation of the cortex. The cortex occurs in the space between the two membranes. This stage also involves the addition of calcium and dipicolinic acid.
Stage 5 — Formation of a spore coat around the cortex.
Stage 6 — Maturation of the endospore
Stage 7 — Final spore maturation, and in some species, enzymes are produced that degrade the mother cell, thus releasing the endospore.
 |
Endospores are quite beneficial to bacteria that produce them since they ensure their survival during adverse conditions. They help to preserve the genetic material of bacteria for a very long time. The resistant properties of endospores to heat, chemicals, radiation, and desiccation lower the bacteria DNA degradation rate. These endospores later germinate upon favorable environmental conditions.
The formation of an endospore occurs once there is a nutrition deficiency of nitrogen or carbon. A dense population that contributes to the competition of available resources may also be a factor of an endospore formation. In addition, harsh environmental conditions such as drought lead to the formation of an endospore. However, endospores cannot form where nutrients are abundant, for instance, in the gut of a human or an animal. The formation of an endospore occurs in seven stages, as described previously.
Even though endospores are resistant to destruction, 2 percent glutaraldehyde has been shown and approved to kill most of the vegetative microbes that produce endospores. However, this disinfectant is unable to destroy the DNA of some bacteria endospores.
Endospore Forming Bacteria
The most common bacteria that are known to form endospores are Bacillus and Clostridium species. Some of these examples include;
- Bacillus subtilis
- Bacillus spharicus
- Bacillus anthracis
- Bacillus cereus
- Clostridium botulinum
- Clostridium perfringens
- Clostridium tetani
- Clostridium difficile
Most bacteria forming endospores are known to cause serious health problems. For instance, some canned food may be contaminated with endospores of Clostridium botulinum or Clostridium difficile. Once these endospores are ingested, due to the conducive conditions of the gut, they get reactivated and start germinating. They rapidly replicate, causing infection to the host. Clostridium botulinum causes botulism, while Clostridium difficile causes antibiotic-related colitis. Antibiotic-related colitis occurs when antibiotics are used to treat this infection. The antibiotic is only able to kill the existing bacteria in the gut but not the Clostridium difficile endospores. This factor contributes to the over multiplication of Clostridium difficile in the colon, causing its inflammation.
Some other diseases caused by bacteria endospores are:
- Anthrax- This is caused by Bacillus anthracis endospores. The infection occurs once the endospores get inhaled, then they germinate and replicate inside the host body.
- Gas gangrene- This is caused by Clostridium perfringens. Once the endospores land on an open wound, they germinate and replicate. They start producing toxins that release gases responsible for tissue damage.
- Tetanus- Clostridium tetani endospores cause this infection. Their entrance into the body through a cut leads to their germination and replication.
- Food poisoning- This is also caused by Bacillus cereus and Clostridium botulinum endospores. It occurs once these spores get ingested. Since the spores are heat resistant, they cannot be destroyed by the heat during cooking.
The germination of endospores occurs once the environmental conditions are conducive and can support the bacteria's growth. This could be nutrient sufficiency (carbon and nitrogen abundance) or lower population density. The germination of endospore occurs in three stages:
1 Activation- This stage makes the endospore ready for germination. Temperature changes, e.g., heat, can cause activation.
2 Germination- Nutrients or metabolites can trigger this stage. During this stage, the spore swells, ruptures, releases the spore contents, loses its resistance traits, and increases its metabolic activity.
3 Outgrowth- The development of active bacteria characterizes this stage. This occurs after the spore protoplast synthesizes new components and releases from the spore coat.
 |
Bacteria are one of the oldest microbes on earth. They are believed to have existed more than 3.5 billion years ago. Their existence could be attributed to their ability to form endospores. Endospores are spores that are formed within the cells, mainly in bacteria. These spores are formed within bacteria vegetative cells or mother cells known as sporangia. Endospores ensure the survival of bacteria in adverse environmental conditions such as nutrient deficiency (carbon and nitrogen) and overpopulation. In addition, endospores are highly resistant to heat, radiation, chemical disinfectants, or desiccation. The most common bacteria that form endospores are Bacillus and Clostridium species.
The formation of an endospore occurs once there is nutrition deficiency of nitrogen or carbon, dense population, and harsh environmental conditions such as drought. Endospores cannot form where nutrients are abundant, for instance, in the gut of a human or an animal. Their formation occurs in seven stages, and their germination occurs in three stages: activation, germination, and outgrowth. Most endospores are destroyed by glutaraldehyde. Finally, endospores cause diseases such as botulism, anthrax, gas gangrene, food poisoning, antibiotic-related colitis, and tetanus. Antibiotic-related colitis is caused by Clostridium difficile, and this infection does not respond well to treatment since the endospores are not affected by antibiotics.
Video Transcript
Ancient Bacteria
In the early 1980s, archaeologists discovered a 7,500-year-old bacteria in lake sediment. This probably sounds incredible. You may be thinking that no viable organism could possibly be older than that. Would you believe that the record for the oldest living organism not only beats the age of the lake sediment bacteria but completely blows it away? And, by blows it away, I mean by 25 million years!
The champion is a member of the bacterial genus Bacillus. And, by the end of this lesson, you will understand exactly why this is the bacteria you should suspect. Bacillus was found in 1995 in the stomach of a fossilized bee that had become trapped in amber around 25 million years ago. The scientists who discovered the bee were able to examine its stomach contents and found some very interesting things: viable bacterial endospores.
But, before we hand out the award to the bee stomach Bacillus, there is considerable controversy surrounding how to prove how old DNA is and what constitutes a living organism. So, don't be surprised if a new champion emerges as scientists explore new environments that could harbor extremely old bacteria. Now, back to those endospores.
Endospores
I said at the beginning that the 25 million-year-old bacteria were alive, then said that the scientists found endospores, not cells (as you might expect from living bacteria). So, what is an endospore?
An endospore is an extremely resistant dormant cell structure produced by some bacterial species. If you break down the term endospore, 'endo-' means 'inside' and '-spore' refers to the 'dormant structure,' so the endospore is a structure formed inside the cell. There are many examples of endospore-forming bacteria. The two most common are Clostridium and Bacillus. In favorable conditions, these bacteria are actively growing and dividing cells. If a nutrient, such as carbon or nitrogen, becomes scarce or if the population becomes too dense, the bacteria can become stressed. They will enter a stasis phase, which is their equivalent of survival mode. The bacteria can survive in stasis until better growth conditions return. This is kind of similar to the science-fiction concept of cryogenic preservation, where a human body could be frozen in stasis until some distant time in the future, when they can be thawed and resume living.
Formation
So, now that we understand why a cell would form an endospore, how exactly do bacteria make endospores? We just discussed endospore formation as a strategy employed by some bacteria to survive in unfavorable conditions. Well, when these conditions are encountered, the process of sporulation begins, which is simply the process of endospore formation.
During the first phase of sporulation, the bacterium will replicate its DNA and undergo an incomplete cell division. The cell division is incomplete because one copy of the DNA will segregate to a small region of the cell and be engulfed into the original mother cell membrane. This smaller cell that results from the initial sporulation process is called the prespore. It will eventually become the mature endospore, while the larger mother cell will end up degrading.
Inside the prespore is a small amount of cytoplasm, the bacterial DNA, and dipicolinic acid. Dipicolinic acid stabilizes the DNA and proteins, preventing degradation during stasis. The mother cell then lays down thick layers of peptidoglycan and protein to act as a protective and resistant coat on the outside of the endospore. With the coat in place, the mother cell degrades, leaving behind a mature endospore.
One key thing you must remember is that sporulation is not reproductive. When Clostridium and Bacillus need to reproduce, they undergo the classic process of binary fission like other bacteria. In contrast, during sporulation, the cell does replicate the DNA chromosome, but only the mature endospore remains at the end of the process. Instead of two new growing cells, there is a single endospore in a new dormant life stage.
Germination
When favorable conditions return, endospores can quickly come out of stasis and begin growing again. The process usually requires three steps: activation, germination, and outgrowth. The activation process is not entirely understood, but activation can usually be accomplished by an increase in the temperature of the endospore for a minute or two, though not so high as to kill the endospore. Activation triggers the next step: germination. During germination, the protective coat softens and the dipicolinic acid is released. In the final step, outgrowth, water is taken up, the cell swells, and new DNA, RNA, and proteins are synthesized. The newly emerged cell is now fully out of dormancy and can grow and divide again.
Features of Endospores
Now that we know the why and how of endospores, let's take a look at some of the major features. Endospores are generally considered the most resistant living structures known. Endospores are able to resist desiccation (which just means drying), extreme heat and cold, radiation, chemical reactions, acids, and the effects of long periods of time, as illustrated by the endospores found in the bee belly.
Endospores have survived boiling for two hours, submersion in 70% ethanol for 20 years, and upwards of one million rems of radiation. As a comparison for that last one, humans usually die if exposed to only 500 rems.
What I find the most fascinating, however, is that even after all that abuse, returning the endospore to favorable conditions for even minutes will cause the protective coat to break down and the cell to begin growing!
Killing Endospores
Endospores are not indestructible despite nature's attempt at making them so. In laboratory and hospital settings, the best way to eliminate endospores is the autoclave. An autoclave is a machine that uses steam coupled with very high temperatures and pressures to sterilize objects and liquids.
What if you need to sterilize something that will melt, like some plastics or large pieces of machinery? There are also a few chemicals capable of inactivating endospores. Gases such as ethylene oxide and chlorine dioxide are capable of killing endospores, but these gases can be dangerous to work with and harmful to humans. The liquid glutaraldehyde is also sporicidal. As with the gases, this chemical is unstable and potentially dangerous to the people using it. Common bactericidal chemicals like bleach, phenols, and alcohols usually have absolutely no effect on endospores, making the more dangerous chemicals a necessary risk.
Endospores and Disease
You might assume that if the methods for eliminating endospores are so toxic to humans, why take the risk of exposure? Why can't we just let the endospores be? Typically with bacteria, the answer is disease. Several very serious illnesses are caused by spore-forming bacteria. Perhaps the most serious is anthrax. Bacillus anthracis is the causative agent of anthrax and also a spore-former. Anthrax spores that get inhaled or contaminate a wound will quickly germinate and begin secreting toxins.
The genus Clostridium also forms spores and causes disease. Tetanus, botulism, and gas gangrene can result from Clostridium spores germinating in a favorable environment. Clostridium requires an environment without any oxygen present, so any wounds, dead tissues, or vacuum-sealed foods could be a potential growth medium.
Another infamous endospore-forming bacteria is Clostridium difficile, which you may have heard called C. diff. These bacteria invade the intestines of sick patients, where they can form endospores that survive antibiotic treatment. After the antibiotics wear off, the endospores can germinate and cause severe gastrointestinal disease and sometimes death.
Lesson Summary
Let's take a quick look back at what we've just learned. Bacteria in the genera Bacillus and Clostridium are able to enter a state of dormancy during unfavorable growth conditions. These bacteria form endospores that are extremely resistant to environmental extremes, chemical degradation, and the effects of time. When conditions improve, the endospores can germinate and rapidly return to normal growth.
While in endospore form, most common disinfectants and sterilization methods are unable to penetrate the endospore coat. But, endospores are susceptible to the effects of autoclaves, glutaraldehyde, and sterilizing gases, although these gases and chemicals pose risks to the people using them.
Several endospore-forming bacteria pose a significant threat as disease-causing organisms. Bacillus and Clostridium endospores can be inhaled or infect wounds as well as survive antibiotic treatments, leading to rebound infections.
Learning Outcomes
At the end of this lesson, you'll be able to:
- State what endospores do and how they are formed
- Recall the three steps that endospores go through when they come out of stasis
- Outline techniques for killing spore-forming bacteria and point out some negative effects of these methods
- Name two common endospore-forming bacteria and the diseases they cause
Register to view this lesson
Unlock your education
Become a Study.com member and start learning now.
Become a memberAlready a member? Log in
Go backResources created by teachers for teachers
I would definitely recommend Study.com to my colleagues. It’s like a teacher waved a magic wand and did the work for me. I feel like it’s a lifeline.
