Ejectosome

An ejectosome is a cellular organelle responsible for ejecting their contents from the cell. Two unrelated types of ejectosomes are described in the literature:

1. Cryptomonads have two types of characteristic ejectisomes known as extrusomes.
2. Intracellular pathogens, such as Mycobacterium tuberculosis, escape from their host cells using an actin-based structure, also called an ejectosome.

Cryptomonad ejectosomes contain two connected spiral ribbon-like structures, held under tension.^[1] If the cells are irritated either by mechanical, chemical or light stress, they discharge, propelling the cell in a zig-zag course away from the disturbance. Large ejectisomes, visible under the light microscope, are associated with the pocket; smaller ones occur elsewhere on the cell.^[2]

Mycobacteria are ejected from host cells through the action of an actin-based ejectosome. This escape mechanism requires a cytoskeleton regulator from the host plus an intact mycobacterial ESX-1 secretion system. Ejectosomes apparently exert a contractile force, forming a tight septum around the bacteria. Ejection of the bacteria occurs without host cell lysis.^[3]

References

1. ↑ Cryptophyte With Ejectosome Electron Micrograph.
2. ↑ Cryptomonads = Goniomonas + plastid-containing cryptophytes.
3. ↑ Hagedorn, M. et al. Infection by Tubercular Mycobacteria Is Spread by Nonlytic Ejection from Their Amoeba Hosts. Science 27 March 2009: Vol. 323. no. 5922, pp. 1729 - 1733.