A
microbial cyst is a resting or
dormant stage of a microorganism, usually a
bacterium or a
protist or rarely an
invertebrate animal, that helps the organism to survive in unfavorable environmental conditions. It can be thought of as a state of
suspended animation in which the
metabolic processes of the cell are slowed and the cell ceases all activities like feeding and locomotion.
Encystment, the formation of the cyst, 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. In excystment, the exact stimulus is unknown for most protists.
[1]
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
[2] trigger the formation of a cyst.
The main functions of cysts are to protect against adverse changes in the environment such as nutrient deficiency, desiccation, adverse pH, and low levels of oxygen, they are sites for nuclear reorganization and cell division, and in parasitic species they are the infectious stage between hosts.
[3]
