Metabolic Diversity of Bacteria

If there is a group of beings that has great metabolic diversity, it is certainly that of bacteria.

There are species heterotrophs and species autotrophs. Among the first, we highlight the parasites, the decomposers of organic matter and those that obtain organic matter from other living beings, with which they associate without harming them. Among the autotrophs, there are species that produce organic matter by photosynthesis and others that produce by chemosynthesis.

Heterotrophic Bacteria

At parasitic bacteria They are those that, through innumerable mechanisms, attack other living beings to obtain organic food and cause innumerable diseases. At decomposers (often called sapróvoras, saproffitic or sapraghagic) obtain organic food through decomposition of dead organic matter and are important in the recycling of mineral nutrients in the biosphere.

Those associated with other living things are called symbionts, and do not harm partners. It is the case of bacteria found in the stomach of ruminants (oxen, goats), which nourish the cellulose ingested by these animals, providing, in turn, amino acids essential for their protein metabolism.

Many heterotrophic bacteria are mandatory anaerobes, like the tetanus bacillus. These are bacteria that die in the presence of oxygen. In this case the energy of the organic compounds is obtained by fermentation. Facultative anaerobes, on the other hand, live both in the presence and absence of oxygen.

Other species survive only in the presence of oxygen - they are the obligatory aerobics. A curious group of bacteria is what accomplishes the aerobic breathing. In this mode of energy metabolism there are all the typical stages of cellular respiration. It only changes the final electron acceptor in the respiratory chain. In place of oxygen, these bacteria use nitrate, nitrite or sulfate, achieving in the end practically the same energy yield as aerobic cellular respiration. that's what happens with bacteria denitrifying agents that participate in the nitrogen cycle in nature. In them the final electron acceptor is nitrate.

Autotrophic Bacteria


In photosynthetic bacteria, solar energy is captured by a chlorophyll known as bacteriochlorophyll. From the use of simple substances in the environment, the synthesis of biofuel occurs. In general, there is no release of oxygen. As an example, we can mention the sulphorous bacteria of the genus Chlorobium, which carry out this process with the use of H2S and CO.2, according to the equation:

2H2S + CO2 + light --bacteriochlorophyll ---> (CH2) + 2S + H20

Note that it is hydrogen sulphide, not water, that acts as a hydrogen supplier that will serve to reduce carbon dioxide. There is no release of oxygen. Sulfur remains inside bacterial cells and is subsequently eliminated into the environment in which these microorganisms live, usually sulfur sources. In this process, CH2O represents the organic matter produced.


Chemosynthesis is a reaction that produces chemical energy, converted from the binding energy of oxidized inorganic compounds. Being the released chemical energy, used in the production of organic compounds and oxygen gas (O2) from the reaction between carbon dioxide (CO2) and molecular water (H2O) as shown below:
- First step

Inorganic Compound + O2 → Oxidized Inorganic Compounds + Chemical Energy

- Second stage

CO2 + H2O + Chemical Energy → Organic Compounds + O2

This autotrophic process of synthesis of organic compounds occurs in the absence of solar energy. It is a resource commonly used by some species of bacteria and archaebacteria (bacteria with primitive characteristics still in force), being named after the reactive inorganic compounds, and may be: ferrobacteria and nitrobacteria or nitrifying (nitrossomonas and nitrobacter, genus of chemosynthetic bacteria).
At ferrobacteria oxidize iron-based substances to achieve chemical energy, whereas nitrifying, use nitrogen based substances.
Present on the ground, nitrosomonas and nitrobacter, are important organisms considered nitrogen biofixers, usually found freely in the soil or associated with plants, forming root nodules.
Biofixation begins with assimilation into atmospheric nitrogen (N2), turning it into ammonia (NH3), a reagent oxidized by nitrosomone, resulting in nitrite (NO2-) and energy for the production of sustainable organic substances for this genus of bacteria.
Nitrite, released into the soil and absorbed by nitrobacter, also undergoes oxidation, generating chemical energy for the production of organic substances for this genus and nitrate (NO3-), used by plants in the preparation of amino acids.
Chemosynthetic reaction in Nitrosomones:

NH3 (ammonia) + O2 → NO2- (nitrite) + Energy
6 CO2 + 6H2O + Energy → C6H12O6 (Glucose - Organic Compounds) + 6 O2

Chemosynthetic reaction in Nitrobacter:

NO2- (nitrite) + O2 → NO3- (nitrate) + Energy
6 CO2 + 6H2O + Energy → C6H12O6 + 6 O2

Thus, we can see that the chemosynthesis mechanism, extremely important for the survival of nitrifying bacteria, is also very relevant to humans. As already mentioned, plant-absorbed nitrite, converted into amino acids, serves as the base of amino acids essential to human nutrition (an omnivorous being: carnivore and herbivore).
Thus, the interdependence between biotic factors (the diversity of organisms) and abiotic factors (physical and chemical aspects of the environment) is evident.