Difference Between Endospore and Exospore

Main Difference – Endospore vs Exospore

Endospore and exospore are two types of spores produced by organisms. The main difference between endospore and exospore is that endospore is produced inside the cell wall of the mother cell and released to the environment by the cell rupture whereas exospore is produced by the cell division and is separated from the mother cell by the formation of a septum. Endospores are mainly produced by bacteria as resistant units to overcome harsh environmental conditions. In contrast, exospores are produced by fungi and algae during the asexual reproduction. Both endospore and exospore can be considered as reproductive cells since they germinate to produce a new organism.

Key Areas Covered

1. What is an Endospore
     – Definition, Characteristics, Function
2. What is an Exospore
     – Definition, Characteristics, Function
3. What are the Similarities Between Endospore and Exospore
     – Outline of Common Features
4. What is the Difference Between Endospore and Exospore
     – Comparison of Key Differences

Key Terms: Algae, Asexual Reproduction, Bacteria, Endospore, Exospore, Fungi, Reproductive Cells

What is an Endospore

An endospore is a resistant structure produced by bacteria to survive under unfavorable environmental conditions. Endospores contain DNA and a small cytoplasm, which is surrounded by a protective outer covering. Endospores germinate to produce new organisms when the environmental conditions become favorable. Therefore, endospores are considered as a type of reproductive cells. The bacterial genera, Bacillus, Clostridium, and Paenibacillus produce endospores. These endospores can withstand harsh conditions such as dehydration, high and low temperatures, chemicals, and UV radiation.

Figure 1: Bacillus endospores (green)

The cell wall of an endospore is made up of dipicolinic acid, which gives heat resistant properties to the endospore. The treatment of moist heat at 121 °C for 15 minutes may destroy bacterial endospores. The Bacillus endospores are shown in figure 1.

What is an Exospore

Exospore is another resistant bacteria produced mainly by fungi and algae to reproduce under unfavorable conditions. Exospores develop from the end of the mother cell by cell division. The separation of the exospore occurs by the formation of a septum between the mother and the daughter cell. The exospore comes out as a bud. Under favorable conditions, the bud is released from the mother cell for the germination. Conidiophores are a type of fungal spores, which are produced as exospores.

Figure 2: Exospores

The algae such as Chamaesiphon and Stichosiphon produce exospores. Bacteria such as Actinomyces, Streptomyces, and Actinobacteria produce exospores. The cyanobacteria like Chamaesiphon also produce exospores. The conidiophores of Aspergillus is shown in figure 2.

Similarities Between Endospore and Exospore

• Endospore and exospore are two types of spores produced by bacteria, fungi, and algae.
• The process of producing spores is called the sporulation.
• Typically, both endospores and exospores are produced in unfavorable environmental conditions.
• Both endospore and exospore can be considered as reproductive cells.
• Both endospores and exospores are unicellular.
• Both endospores and exospores are highly resistant structures.
• Both endospores and exospores can retain without nutrients since they comprise very low metabolic rates.

Difference Between Endospore and Exospore

Definition

Endospore: Endospore is a structure formed by bacteria to survive under unfavorable environmental conditions, consisting of DNA and a small amount of cytoplasm.

Exospore: Exospore is an asexual spore that is separated from the mother cell by the formation of a septum.

Produced by

Endospore: Endospores are produced by bacteria.

Exospore: Exospores are produced by fungi and algae.

Formation

Endospore:  Endospores are produced inside the mother cell.

Exospore:  Exospores are produced near an end of a mother cell.

Cell Division

Endospore: Cell division is not involved in the formation of endospores.

Exospore: Exospores are produced by the cell division.

Release of the Spore

Endospore: The endospores are released by rupturing the mother cell.

Exospore: The exospores are released by budding.

From an Organism

Endospore: Only one endospore can be produced per one organism.

Exospore: Several exospores can be produced by one organism.

Examples

Endospore: Exospores are produced by the bacterial genera, Bacillus, Clostridium, and Paenibacillus.

Exospore: The conidiospores, Chamaesiphon, Stichosiphon, Actinomyces, Streptomyces, Actinobacteria, Chamaesiphon produce exospores.

Conclusion

Endospore and exospore are two types of spores produced as resting units. Endospores are mainly produced by bacteria. Exospores are produced by fungi, algae, cyanobacteria, and bacteria. Endospores are produced inside the mother cell. But, exospores are produced at the end of the mother cell and released as a bud. This is the difference between endospore and exospore.

Reference:

1. “Endospores – Boundless Open Textbook.” Boundless, 26 May 2016, Available here. Accessed 22 Aug. 2017.
2. “Spores.” VetBact, Available here. Accessed 22 Aug. 2017.

Image Courtesy:

1. “Bacillus subtilis Spore” By Y tambe (original uploader) – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. Image 2 (CC0) via Pixino

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