Anaerobic organism

An anaerobic organism or anaerobe is any organism that does not require oxygen. Obligate anaerobes will die when exposed to oxygen, while facultative anaerobes can use oxygen when present. Aerotolerant organisms do not require oxygen, but are not affected by exposure to air.

There are many chemical equations for anaerobic fermentative reactions.

Anaerobic animals mostly use the lactic acid fermentation pathway:

C₆H₁₂0₆ + 2 ADP + 2 phosphate → 2 lactic acid + 2 ATP

The energy released in this equation is approximately 150 kJ per mol, which is conserved in regenerating two ATP from ADP per glucose.

Plants and fungi (e. g. yeasts) generally use alcohol (ethanol) fermentation when oxygen becomes limiting:

C₆H₁₂0₆ + 2 ADP + 2 phosphate → 2 C₂H₅OH + 2 CO₂ + 2 ATP

The energy released is about 180 kJ per mol, which is conserved in regenerating two ATP from ADP per glucose.

Anaerobic bacteria and archaea use these and many other fermenative pathways, e. g. propionic acid fermentation, butyric acid fermentation, solvent fermentation, mixed acid fermentation, butanediol fermentation, Stickland fermentation, acetogenesis or methanogenesis.

Some anaerobic bacteria produce toxins (e. g. tetanus or botulinum toxins) that are highly dangerous to higher organisms, including humans.