Spores are broadly classified into two different types depending on the position, which are known as Endospore and Exospore. Two types of reproductive structures or spores are Endospore and Exospore which are produced as stationary or resting systems. The most common types of spores i.e endospores are generally produced by bacteria. External spores or exospores are formed in the eukaryotic cells of algae, cyanobacteria and fungi. Both the spores grow to develop a new organism. So, they can be considered as germ cells. Both the endospore and exospore have very low metabolic rates and hence remain non-nutritive. Both the internal and external spores are highly resistant structures and are unicellular.
(Image to be added soon)
Endospores are dormant, resistant, and tough structures produced by some bacteria which allows them to overcome the unfavorable environmental conditions. Endospores are produced by bacterial genera such as Bacillus anthracis, Bacillus thuringiensis, Clostridium botulinum, Bacillus cereus, Clostridium tetani.
They comprise of DNA and a small amount of cytoplasm which is surrounded by a protective outer shell. The endospore cell wall is made up of dipicolinic acid which provides the endospore properties of heat resistance. Bacterial endospores may be destroyed by the humid or moist heat treatment done at 121°C for 15 minutes.
Endospores sprout new organisms when the environmental conditions become favorable. Hence, internal spores can be considered as a type of reproductive or germ cells. Endospores are quite resistant to high temperatures and can withstand adverse conditions like toxic chemicals, dehydration, and UV radiation.
Exospores are also bacterium resistant structures produced by algae and fungi which reproduce asexually under harsh conditions. External spores are produced by cell division either at the end or the surface of the parent cell. Separation of exospores occurs by the formation of a septum or barrier between the daughter and the mother cell. They are released by budding during the favorable conditions as exposures sprout and the bud is released from the mother cell for the process of germination.
Algae which produce exospore are Chamaesiphon and Stichosiphon.
Fungal spores which produce exospore are Conidiophores.
Bacteria that produce exospores are Actinomyces, Streptomyces, and Actinobacteria.
Cyanobacteria which produce exospore are Chamaesiphon.
(Image to added soon)
(Image to be added soon)
The main key difference between endospore and exospore is that the production of endospore occurs inside the cell wall of the mother cell whereas the production of exospore results due to the involvement of cell division and through the barrier.
Endospores are released in the environment by rupturing or tearing of the cell. In contrast, the formation of a septum results in the separation of exospore from its mother cell.
Endospores are resistant units produced by bacteria to overcome adverse environmental conditions whereas fungi and bacteria produce exospore during asexual reproduction.
Endospores are also known as "resting cells" whereas Exospores is high resistible to desiccation and heat.
Endospores are dehydrated cells which are highly durable and can survive under the adverse heat conditions, radiation, and toxic chemicals and also in the immense freezing conditions. They contain dipicolinic acid. In contrast, Exospore does not contain dipicolinic acid.
1. What Are Spores And What Is Sporulation?
Spores are unicellular, solitary, and reproductive structures. Spores occur in shapes, sizes, variables, and numbers. These reproductive structures are highly resistant to adverse environmental situations such as temperatures (low or high pH, salt concentration, dehydration, toxic chemicals conditions, etc. Spores are usually divided into two categories on the basis of situation or position which are:
Endospore or internal spore
Exospore or external spore
The process of production of spores by the vegetative cells is known as Sporulation. Sporulation is also named as sporogenesis. Sporulation gives a multilayered structure that is useful as it can be maintained for a long time.
2. What Makes The Endospore And Exospore Resistant To Desiccation?
Both endospore and exospore show resistant properties which make them resistant to desiccation. These resistance characteristics involve relatively impermeable inner membrane of the spore which restricts toxic chemicals to access the spore core which includes most of the enzymes and DNA of the spore, the spore's outer layer like the thick protein implemented coat which function as a detoxifier and hence detoxifies the reactive chemicals and also dipicolinic acid which is present in high level and the low water content in the spore core which protects the macromolecules of core from the impacts of desiccation and heat.