by Microbiology Doctor-dr
NUTRITION IN BACTERIA
Nutrition
Nutrition is the process of obtaining energy and resources. Bacteria must eat carbon, energy, and electrons to survive. Light and chemical energy are the primary sources of energy for bacteria, whereas carbon and electrons are derived from inorganic or organic substances. Furthermore, bacteria require nitrogen, sulphur, and phosphorus for sustenance. Some bacteria get nitrogen from the air, while others get it from inorganic nitrogen compounds like nitrates, nitrites, or ammonia salts, and still others get it from organic compounds like amino acids. Sulphur is required for the synthesis of cysteine, cystine, and methionine, among other amino acids. Organic sulphur compounds are required by some bacteria, while inorganic sulphur compounds and elemental sulphur are used by others. Phosphorus is found in nucleotides, nucleic acids, phospholipids, and other compounds. Phosphate is the most common form of supply.
Nutritional Types of Bacteria
On the basis of their nutritional requirements, bacteria can be divided into two categories: autotrophic and heterotrophic bacteria.
1. Autotrophic Bacteria
Autotrophic bacteria are those that can generate organic chemicals necessary for their life from simple inorganic sources. Carbon is obtained from inorganic molecules, primarily carbon dioxide.
The autotrophic bacteria are further classified into photoautotrophs and chemoautotrophs.
i. Photoautotrophs
Photoautotrophs are bacteria that use light as their energy source. Because these bacteria have chlorophyll, they can manufacture their own nourishment. Photosynthetic bacteria are another name for these bacteria. The structure of bacterial chlorophyll is similar to that of plant chlorophyll, however it is not found in the chloroplasts. It is spread throughout the bacteria's cytoplasm. Photosynthetic bacteria get their energy from sunlight. In these bacteria, the hydrogen source is H2S (hydrogen sulphide), rather than water, and sulphur is produced throughout the process.
Light
2H2S + CO2 -------------------------------- [CH2O] + 2S + H2O
bacteriochlorophyll
The photoautotrophs may be:
a. Purple Sulphur Bacteria: The bacteria which use Sulphur compounds as source of electrons and protons, for example Chromatum okenii.
2CO2 + 5H2O + Na2S2O3 -------------------- 2(CH2O) + 2H2 + NHSO2 + energy
b. Green Sulphur Bacteria: These bacteria use H2S as source of electrons and protons, for example Chlorobium and Chlorobacterium.
2H2S + CO2 ----------------------- [CH2O] + 2S + H2O
c. Purple Non-Sulphur Bacteria: These bacteria use organic compounds as source of electrons and protons, for example Rhodospirullum rubrum which use propyl alcohol.
2CH3CHOHCH3 ------------ CH2O + CH2COCH3 + H2O
ii. Chemoautotrophs:
Chemoautotrophs are bacteria that get their energy from the oxidation of inorganic chemical compounds during respiration. These bacteria serve a vital role in the biosphere, primarily in maintaining soil fertility via their nitrogen cycle activities.
Chemosynthetic bacteria are further divided into:
a. Nitrifying Bacteria: These bacteria, such as Nitrosomonas and Nitrobacter, live in the soil and oxidise ammonia to nitrites or nitrites to nitrates. These bacteria use the energy released in the manufacture of food.
Nitrosomonas
2NH3 + 3O2 ----------------- 2HNO2 + 2H2O + 158 Kcals.
Nitrobacter
2HNO2 + 3O2 ------------------- 2HNO3 + 43 Kcals.
b. Iron Bacteria: In iron-rich water, these bacteria are frequently found. These bacteria get their energy by converting ferrous molecules to ferric ones. Leptothrix, Cladothrix, and Spiruphyllum are some instances of ferrugineum and Ferrobacillus.
2Fe(HCO3)2 + H2O + O ----------------- 2Fe(OH)3 + 4CO2 + 29 Kcals.
4FeCO3 + O2 + 6H2O ------------ 4Fe(OH3) + 4CO2 + 81Kcals.
c. Sulphur Bacteria: These bacteria can be discovered in hydrogen suplhide-rich hot springs. To obtain energy, they oxidise metallic sulphide to sulphur. Beggiatoa and Thiothrix are two common examples.
d. Hydrogen Bacteria: These bacteria can oxidise hydrogen with the release of energy and grow on organic media containing hydrogen, carbon dioxide, and oxygen. Bacillus panctotrophus is one of them.
2H2 + O2 ---------- 2H2O + 137 Kcals.
2H2 + CO2 ------------- (CH2O) + H2O + 118 Kcals.
e. Methane Bacteria: Methane is converted to carbon dioxide by these microorganisms. Methane, for example, provides both carbon and energy to bacteria like Methanosomonas.
CH4 + 2O2 --------------- CO2 + 2H2O + energy
2. Heterotrophic Bacteria
Heterotrophic bacteria are those that get their energy from organic molecules produced by other species. Because these bacteria are unable to prepare their own food, they must rely on outside sources.
Most bacteria are heterotrophic and can be classified into:
i. Saprotrophic Bacteria
Bacteria that feed on dead and decaying substances, such as humus These bacteria have an enzyme system of their own. They produce enzymes that break down complicated organic chemicals into simpler components. The bacteria absorb these compounds and utilise them as a source of energy. Because they break down or disintegrate complex organic compounds and release simpler substances into the environment, these bacteria are also known as decomposers. Living organisms are once again using these simpler chemicals (recycling of nutrients).
ii. Parasitic Bacteria:
Because these bacteria are heterotrophic yet lack an enzyme system, they are unable to produce food from simple organic compounds. For their survival, they rely on the enzymes of other living species (hosts) to produce food. Disease is caused by a variety of parasite microorganisms. These bacteria are known as pathogens or virulent bacteria, such as Pneumococcus, which causes pneumonia.
iii. Symbiotic Bacteria
Certain bacteria, such as Rhizobium radicicola, create symbiotic relationships with the roots of leguminous plants. They create nodules, fix atmospheric nitrogen, feed nitrogenous substances to plants, and receive nourishment from plants in return.
