Microbial cyst

Cyst stage of Entamoeba histolytica

A microbial cyst is a resting or suspended animation in which the metabolic processes of the cell are slowed down and the cell ceases all activities like feeding and locomotion. Encystment also helps the microbe to disperse easily, from one host to another or to a more favorable environment. When the encysted microbe reaches an environment favorable to its growth and survival, the cyst wall breaks down by a process known as excystation.

Unfavorable environmental conditions such as lack of nutrients or oxygen, extreme temperatures, lack of moisture and presence of toxic chemicals, which are not conducive for the growth of the microbe ^[1] trigger the formation of a cyst.

Cyst formation across species

In bacteria

In bacteria (for instance, Azotobacter sp.), encystment occurs by changes in the cell wall; the cytoplasm contracts and the cell wall thickens. Bacterial cysts differ from endospores in the way they are formed and also the degree of resistance to unfavorable conditions. Endospores are much more resistant than cysts.

In protists

Protists, especially trophozoites upon excystation.^[2]

In nematodes

Some soil-dwelling plant parasitic nematodes, such as the soybean cyst nematode, or the potato cyst nematode form cysts as a normal part of their lifecycle.

Composition of the cyst wall

The composition of the cyst wall is variable in different organisms. The cyst walls of bacteria are formed by the thickening of the normal cell wall with added peptidoglycan layers whereas the walls of protozoan cysts are made of chitin,^[3] a type of glycoprotein. Nematode cyst walls are composed of chitin reinforced by collagen.

See also

• Spore (in bacteria, fungi and algae)
  • Endospore (in firmicute bacteria)
  • Resting spore (in fungi)
• Trophozoite
• Cryptobiosis

References