Cross section of a bacterial spore showing its hard, multilayered coats, which both make the spore difficult to kill and allow it to remain dormant for many years.
Bacterial spores represent a highly resistant, resting phase displayed by some types of bacteria. Endospores (or simply spores) form within (hence endo-) special vegetative cells called sporangia in response to adverse changes in the environment. The original cell replicates its genetic material, and one copy of this becomes surrounded by a tough coating. The outer cell then disintegrates, releasing the spore which is now well protected against a variety of trauma, including extremes of heat and cold, radiation, and an absence of nutrients, water, or air.
Sporing bacteria are the cause of a number of serious diseases in humans.
Among diseases caused by anaerobic sporing
bacteria are botulism (Clostridium
botulinum), gas gangrene (Clostridium
perfringens), tetanus (Clostridium
tetani) and acute food poisoning (Clostridium perfringens again). Anthrax results from the aerobic sporing bacteria Bacillus anthracis.
In 1995, Raul Cano and Monica Borucki, of California Polytechnic State University in San Luis Obispo, reported having recovered and reanimated bacterial spores from the digestive tracts of bees that had been entombed in amber for between 25 and 40 million years. Similar remarkable claims have been made for the temperature resistance of spores. About one in 100,000 have been shown to survive brief exposure to the 3,000°C flame of a rocket exhaust, while others have emerged unscathed from a bath in liquid helium at -269°C. These findings are cited as evidence by proponents of panspermia that spores might be able to travel for millions of years across interstellar distances yet remain viable.