The metabolism among the bacteriae is done through many different forms, depending upon how the bacteria assimilates vital gases from the environment. Thus, we can easily distinguish some main forms:

a) heterotrophic bacteriae — these include the saprobiotyc species; heterotrophic bacteriae are decomposers which can be found in the soil or in water. Over 90% of the amount of CO₂ which is present in the biosphere is resulting from the decomposers’ activity. These organisms are also called edaphic bacteriae. Some bacteriae of this group decompose aminate acids, freeing NH₄+. This process is known as amonification. The NH₄+ can be oxidated till it turns into NO₂- by bacteriae of the genum Nitrosomonas. Another important genus of soil bacteriae is Nitrobacter, which converts NO₂- into NO₃-.

b) photosynthetic forms — many genera of the Monera, more specifically three groups besides the cyanophyceae, assimilate carbon from CO₂ having H₂S as basis. The carbohydrate formation (CH₂O) and sulphur liberation (S-) follows the equation:

CO₂ + 2 H₂S > CH₂O + H₂O + 2 S-

The reaction only occurs in the presence of light. Compare this process with the general chemical process of the photosynthesis:

6 CO₂ + 6 H₂O > C₆H₁₂O₆ + 6 O₂

The inconvenient of the first process is that it frees sulphur anion instead of oxygen, which is certainly something uninteresting to mankind.

c) chemiautotrophic bacteriae — this group of bacteriae does not employ sun light, although it requires oxygen. The energy these bacteriae use to lead carbohydrate synthesis comes from the inorganic mollecule oxidation, such as nitrogen compounds (N₂), sulphur (S₂), iron (Fe), hydrogen (H₂) and many other compounds.