Figure 3.20 (a) Sporulation begins following asymmetric cell division. The forespore becomes surrounded by a
double layer of membrane, a cortex, and a protein spore coat, before being released as a mature endospore upon
disintegration of the mother cell. (b) An electron micrograph of aCarboxydothermus hydrogenoformansendospore.
(c) TheseBacillus spp.cells are undergoing sporulation. The endospores have been visualized using Malachite
Green spore stain. (credit b: Jonathan Eisen)
Endospores of certain species have been shown to persist in a dormant state for extended periods of time, up to
thousands of years.[17]However, when living conditions improve, endospores undergogermination, reentering a
vegetative state. After germination, the cell becomes metabolically active again and is able to carry out all of its
normal functions, including growth and cell division.
Not all bacteria have the ability to form endospores; however, there are a number of clinically significant endospore-
forming gram-positive bacteria of the generaBacillusandClostridium. These includeB. anthracis, the causative
agent of anthrax, which produces endospores capable of survive for many decades[18];C. tetani(causes tetanus);
C. difficile(causes pseudomembranous colitis);C. perfringens(causes gas gangrene); andC. botulinum(causes
botulism). Pathogens such as these are particularly difficult to combat because their endospores are so hard to
kill. Special sterilization methods for endospore-forming bacteria are discussed inControl of Microbial Growth
(http://cnx.org/content/m58852/latest/).
- What is an inclusion?
- What is the function of an endospore?
- F. Rothfuss, M Bender, R Conrad. “Survival and Activity of Bacteria in a Deep, Aged Lake Sediment (Lake Constance).”Microbial
Ecology33 no. 1 (1997):69–77. - R. Sinclair et al. “Persistence of Category A Select Agents in the Environment.”Applied and Environmental Microbiology74 no. 3
(2008):555–563.
Chapter 3 | The Cell 101