At least three different clostridia are apparent. Electron micrograph of Clostridium tetani cells. All species form endospores and have a strictly fermentative mode of metabolism. Most clostridia will not grow under aerobic conditions and vegetative cells are killed by exposure to O2, but their spores are able to survive long periods of exposure to air. The clostridia are ancient organisms that live in virtually all of the anaerobic habitats of nature where organic compounds are present, including soils, aquatic sediments and the intestinal tracts of animals.
Clostridia are able to ferment a wide variety of organic compounds.
A variety of foul smelling compounds are formed during the fermentation of amino acids and fatty acids. The clostridia also produce a wide variety of extracellular enzymes to degrade large biological molecules in the environment into fermentable components. Hence, the clostridia play an important role in nature in biodegradation and the carbon cycle. In anaerobic clostridial infections, these enzymes play a role in invasion and pathology. Most of the clostridia are saprophytes but a few are pathogenic for humans.