Anaerobe

One calls anaerobic medium a medium where there is not presence of Dioxygène (O).

A Living organism or an anaerobic mechanism does not need air or Oxygène to function.

For example a Digesteur produces Biogaz in anaerobe.

The Muscle has an anaerobic operation at the beginning of the excitation (lactic Fermentation).

An anaerobic bacterium is a Bactérie for which oxygen is toxic (e.g.: bacteria of the kind Clostridium ).

The whole of the living conditions of the living organisms in a medium without Oxygène is called anaérobiose .

One observes various types of anaerobic organizations:

  • the obligatory anaerobic which die when they are exposed to Dioxygène with atmospheric content, and can indifferently use the Fermentation or the anaerobic Respiration.
  • Those with aerobic optional can use the Dioxygène in presence in the culture medium. In the presence of oxygen, these organizations can use the aerobic Respiration, whereas, in absence of oxygen, part of these organizations ferment and the second carries out a anaerobic Respiration.
  • the organizations aérotolérants can survive in the presence of Dioxygène, but are anaerobic by nature because they do not use the Dioxygène like final acceptor of electrons: They use exclusively the mode Fermentation.
  • the microaérophiles are organizations which can use oxygen, but in tiny concentrations (about the µmole); their developments is inhibited under normal conditions of the oxygen concentration (nearly 200 µmoles). Thus for Nanérobes which can develop only in the presence of concentrations in Dioxygène about the nanomole. The principal mode of breathing of these organizations remains the aerobic Respiration, even if a part can also use the anaerobic Respiration.

Several reactional equations represent the anaerobic digestion:

The organizations with anaerobic digestion generally use the lactic Fermentation:

C 6 H 12 O 6 + 2 ADP + 2 pi → 2 C 3 H 6 O 3 + 2 ATP

where C 6 H 12 O 6 is the Glucose and C 3 H 6 O 3 the Lactic acid .

This reaction releases roughly 150 kJ by mol, which is used to regenerate 2 ATP starting from 2 ADP per molecule of glucose. This accounts for only 5% of the energy which can provide a molecule of glucose concerned in an aerobic breathing.

The plants, the yeasts and the bacteria generally use the alcoholic Fermentation when oxygen becomes the limiting reagent:

C 6 H 12 O 6 + 2 ADP + 2 pi → 2 C 2 H 5 O H + 2 C O 2 + 2 ATP

where C 6 H 12 O 6 is the Glucose and C 2 H 5 O H the ethanol.

Released energy is of 180 kJ by mol which is it also used to regenerate 2 ATP starting from 2 ADP per molecule of glucose.

The anaerobic bacteria and Archaea use these metabolisms among so many others, which one can quote fermentation with the Propanoic acid , with the butanoïque Acide, with butane-diol, fermentation with several acids (in: mixed acid fermentation ), the fermentation of Stickland, the acétogénèse or the méthanogénèse.

A certain number of anaerobic bacteria produce Toxine S (like the Tétanos or the botulinic Toxine) which are potentially dangerous for the organizations, particularly the human ones.

The obligatory anaerobes die in the presence of oxygen because of the absence of enzymes able to catalyze the toxin conversion create in their cells because of presence of Dioxygène.

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