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Spores can be classified into two different types depending on their position, namely Endospore and Exospore. The two types of reproductive structures or spores are Endospore and Exospore. They are produced as stationary or resting systems. The most common type of spores, Endospores are generally produced by bacteria. External spores or Exospores are produced in the eukaryotic cells of cyanobacteria, algae, and fungi. Both Endospore and Exospore grow to form a new organism. So, we can consider them to be germ cells. The metabolic rates for both the Endospore and Exospore are very low and hence they remain non-nutritive. Both the internal and external spores are unicellular and are highly resistant structures. Endospore and Exospore allow the bacteria to survive during unfavorable conditions, such as intense heat, disinfectants, and even UV radiation. Let’s discuss the major differences between endospore and exospore.
| Table of Content |
Key Takeaways: Spores, Germination, Bacterium, fungi, DNA, Sporulation.
Also Read: Reproductive Health
Meaning of Endospore and Exospore
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Endospores are dormant, resilient, and tough spores produced by some bacteria that allow them to overcome adverse environmental conditions. Endospores are produced by a variety of bacterial such as Bacillus anthracis, Bacillus thuringiensis, Clostridium botulinum, Bacillus cereus, Clostridium tetani.
Exospores are bacteria resistant structures that are produced by algae and fungi which perform asexual reproduction under harsh conditions. External spores are produced by cell division at one end or the surface of the parent cell. The separation of exospores occurs by the formation of a septum or barrier between the daughter and parent cell. They are released by germinating during the favorable conditions as exposures sprout and the shoot is released from the mother cell for the cell to germinate.
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Characteristics of Endospore and Exospore
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Endospores comprise DNA and a small portion of the cytoplasm which is surrounded by a protective outer shell. The endospore cell wall is made of di-picolinic acid which gives heat-resistant properties to the endospore. Bacterial endospores can be destroyed by humid or moist heat treatment made at 121°C for 15 minutes.
The exospore initially comes out as a bud. Under favorable conditions, the bud is released from the mother cell for germination. Conidiophores, a type of fungal spores are produced as exospores.
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Functions of Endospore and Exospore
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Endospores germinate new organisms when natural conditions become favorable. Thus, internal spores can be considered as a type of reproductive or germination cells. Endospores are resistant to high temperatures and can withstand adverse conditions like toxic chemicals, dehydration, and UV rays.
Exospore is also referred to as the exine in plant spores. The exospore interacts with its environment or the host body. It may contain spore antigens. Exospore proteins like Cot protein, have also been discovered to be related to strains of B. anthracis and B. cereus. This Cot protein shares similar sequences with other spore coat proteins.
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Differences between Endospore and Exospore
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The basic differences between endospores and exospores are as follows:
| Endospores | Exospores |
|---|---|
| Endospores are resistant bacteria-born structures that are capable of surviving under adverse environmental conditions. | Exospores are another resistant structure produced by algae and fundi and are mostly used for asexual reproduction under unfavorable circumstances. |
| Endospore formation does not involve cell division. | Whereas exospores are produced by cell division. |
| Endospore is produced by bacteria. | Exospore is produced by algae and fungi. |
| Endospores are formed within the vegetative parent cell or the mother cell. | Whereas exospore cells are formed near the end of a mother cell or the surface of the cell. |
| Endospore is released by the rupturing of the mother cell. | Exospore is released by the process of budding. |
| Examples of Endospore- Bacillus, Paenibacllius, Clostridium, etc. | Examples of Exospore- Streptomyces, Stichosiphon, Actinomyces, etc. |
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Points to Remember
- The production of endospore occurs within the cell wall of the mother cell. Whereas, the production of exospore results is due to the involvement of cell division and barrier.
- Endospores are released by rupturing or tearing of the cell. On the other hand, the formation of a septum causes the separation of the exospore and its mother cell.
- Endospores are produced by bacteria to withstand adverse environmental conditions. Whereas fungi and algae produce exospore by asexual reproduction.
- Endospore is a type of spore produced by bacteria. Exospore is a spore produced by fungi and algae.
- Typically, both endospores and exospores are produced in adverse environmental conditions and can retain devoid of nutrients because they have very low metabolic rates.
- Both endospore and exospore are unicellular and can be considered reproductive cells. Endospores are also known as "resting cells". Exospore can withstand high levels of desiccation and heat.
- Endospores are dehydrated cells that are highly durable and are capable of surviving under adverse heat conditions, radiation, and also in immense freezing conditions. They contain di-picolinic acid. However, Exospores do not contain di-picolinic acid.
Sample Questions
Ques. What are the factors that make the Endospore and Exospore resistant to desiccation? (3 marks)
Ans. Both endospore and exospore exhibit anti- desiccation properties. These resistance factors include the relatively impermeable inner membrane of the spore which prevents toxic chemicals to access the core of the spore which includes the majority of the enzymes and DNA of the spore. The spore's outer layer like the thick protein implemented coat which acts as a detoxifier and hence detoxifies the reactive chemicals and also di-picolinic acid which is present in high level, and the low water content in the spore core protects the macro-molecules of the core of the spore from the impacts of desiccation and heat.
Ques. What are spores? Define sporulation. (3 marks)
Ans. Spores are distinct, unicellular, and reproductive structures. Spores occur in variable shapes, sizes, variables, and numbers. These reproductive structures are highly resistant to adverse environmental conditions such as temperatures low or high pH, salinity levels, dehydration, toxic chemicals conditions, etc. Spores are usually divided into two categories on the basis of their form or position, namely: Endospore or internal spore and Exospore or external spore.
The process of spore production by the vegetative cells is known as Sporulation. Sporulation is also called sporogenesis. It provides a multi-layered structure that is useful as it can be held maintained for a long time.
Ques. What causes endospores to form? (2 marks)
Ans. Endospore formation is often caused by a deficiency of nutrients; it is an isolated, dormant form to which the bacterium can reduce itself. The endospore contains the bacterium's deoxyribonucleic acid (DNA), ribosomes, and large amounts of di-picolinic acid.
Ques. What are the characteristics of exospores? (2 marks)
Ans. Initially, the exospore comes out as a bud. Under favorable conditions, the bud is released from the mother cell for germination. Conidiophores, a type of fungal spores are produced as exospores.
Ques. Write a note on the characteristics of endospores. (2 marks)
Ans. Endospores comprise DNA and a small portion of the cytoplasm which is surrounded by a protective outer shell. The endospore cell wall is made of di-picolinic acid which gives heat-resistant properties to the endospore. Bacterial endospores can be destroyed by humid or moist heat treatment made at 121°C for 15 minutes.
Ques. What are the major differences between endospores and exospores? (4 marks)
Ans.
| Endospores | Exospores |
|---|---|
| Endospores are resistant bacteria-born structures that are capable of surviving under adverse environmental conditions. | Exospores are another resistant structure produced by algae and fundi and are mostly used for asexual reproduction under unfavorable circumstances. |
| Endospore formation does not involve cell division. | Whereas exospores are produced by cell division. |
| Endospore is produced by bacteria. | Exospore is produced by algae and fungi. |
| Endospores are formed within the vegetative parent cell or the mother cell. | Whereas exospore cells are formed near the end of a mother cell or the surface of the cell. |
| Endospore is released by the rupturing of the mother cell. | Exospore is released by the process of budding. |
Ques. What are spores? (3 marks)
Ans. Spores are basically unicellular and reproductive structures and are greatly resistant to extreme environmental conditions, for instance, high temperature, pH, salt concentration, and so on. Such reproductive structures are present in variables, sizes, shapes, and numbers. And the process of the formation of spores by the vegetative cells is referred to as Sporulation or Sporogenesis.
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