Nutrition in Bacteria: Modes of Nutrition in Bacteria

Nutrition in Bacteria: Have you ever thought about why prokaryotic organisms like bacteria require nutrition and how they obtain it? Yes, bacteria need energy and nutrients to complete various activities like growth, reproduction, and metabolism. This energy comes from biosynthesis of different types of chemicals and elements present in our environment.

The nutrition in bacteria is mainly autotrophic and heterotrophic. Phototrophic bacteria contain various pigments to synthesise their own food, while heterotrophic bacteria are dependent on other organisms for food. Parasitic bacteria fulfil their nutrition needs or requirements from the host cell. Read this article to know more about nutrition in bacteria and the mode of nutrition in bacteria in detail.

Nutrition in Bacteria: Definition

Nutrition is a process of acquiring energy and food. The need for energy is required for growth, reproduction, and maintenance. The main sources of nutrients in bacteria are carbon, nitrogen, water, phosphorous, iron, and some inorganic salts. Following are types of Bacteria.

Types of Nutrition in Bacteria

There are two types of nutrition found in bacteria. These are given below in a flowchart:

Fig: Types or Modes of Nutrition in Bacteria

1. Autotrophic Bacteria

a) Autotrophic bacteria synthesise their own food from simple inorganic compounds.
b) In this process, energy is obtained from either sunlight or chemically by the oxidation of some inorganic substances like iron, sulphur, nitrogen compounds, etc.
c) Food synthesised by autotrophic organisms is used for their growth and metabolism.
d) Autotrophic bacteria are further divided into two types depending upon the energy utilisation.

A. Photosynthetic Bacteria

a) These bacteria have a green sunlight trapping pigment called bacteriochlorophyll, which captures sunlight.
b) These bacteria are found in the upper layer of ponds or lakes.
c) Bacterial photosynthesis does not release oxygen; such photosynthesis is known as anoxygenic photosynthesis.
d) Hydrogen is provided by the donor substance hydrogen sulphide, and the by-product is sulphur, not oxygen.
e) These are again divided into two types:

i) Green Sulphur Bacteria
In this type of bacteria, the photosynthetic pigment is chlorobium chlorophyll, which uses hydrogen sulfide as a hydrogen donor and by-products sulphur. Example: Chlorobium.

ii) Purple Sulphur Bacteria
The photosynthetic pigment in this process is bacteriochlorophyll present in the chromatophores, and the by-product is sulphur. Example: Chromatium.

B. Chemosynthetic Bacteria

a) Chemosynthetic bacteria prepare their food by using inorganic raw material in the absence of photosynthesis pigment.
b) In this process, chemical energy is obtained from the oxidation of certain inorganic substances such as ammonia, nitrates, ferrous iron, hydrogen sulphides, and some metallic and nonmetallic substances.
c) In this reaction, chemical bonds are broken, and exothermic energy is released, which is used to drive the synthetic processes of the cell.
d) These are again divided into the following types:

i) Sulphur Bacteria (Sulphomonas)
These types of bacteria oxidise elemental sulphur or H₂S and release sulphuric acid or sulphur.
2S + 2H₂O +3O₂ ? 2H₂O + 2S + Energy
Example: Thiobacillus denitrificans
Or, 2H₂S + 4O₂ ? 2H₂O + 2S + Energy
Example: Beggiatoa

ii) Hydrogen Bacteria (Hydromonas)
In this process, molecular hydrogen is oxidized into water.
2H₂ + O₂ ? 2H₂O + Energy
4H₂ + CO₂ ? 2H₂O + CH₄ + Energy
Example: Hydrogenomonas, Pseudomonas.

iii) Iron Bacteria (Ferromonas)
They use chemical energy by oxidation of ferrous compounds into the ferric compounds.
4FeCO₃ + 6H₂O + O₂ ? 4Fe (OH)₃ + 4CO₂ + Energy
Example: Thiobacillus, Ferrobacillus, etc.

iv) Methane Bacteria (Methanomonas)
These types of bacteria get their energy from the oxidation of methane; by-products are water and carbon dioxide.

v) Nitrifying Bacteria (Nitrosomonas)
Bacteria get their energy by oxidation of nitrogen compounds into nitrates.
2NO₂ + O₂ ? 2NO₃ + Energy
Example: Nitrobacter, Nitrosomonas.

vi) Carbon Bacteria:
These types of bacteria oxidize CO into CO_2.
2CO + O₂ ? 2CO₂ + Energy
Example: Bacillus oligocarbophillous

Fig: Autotrophic Bacteria

2. Heterotrophic Bacteria

a) These types of bacteria are not capable of synthesizing their own food. Thus, they live where organic food is readily available either from living organisms or from organic substances.
b) Most of the pathogenic bacteria of humans, other plants, and animals are heterotrophs.
c) Heterotrophic bacteria don’t have pigment, so they cannot capture solar energy.
d) Some heterotrophic bacteria have simple nutritional requirements, while few bacteria require a complex nutritional requirement or specific nutrients like amino acids for their survival. Such organisms are called fastidious heterotrophs.
e) Heterotrophic bacteria are of three types:

A. Saprophytic Bacteria

a) These types of bacteria obtain food by decomposing dead bodies, excreta of animals, dead plants, and their parts.
b) They secrete enzymes that break down complex organic compounds into simpler products.
c) Breakdown of carbohydrates is called fermentation, and breakdown of protein is called putrefaction.
d) Examples of these types of bacteria are Bacillus mycides, Acetobacter, etc.

B. Parasitic Bacteria

a) Parasitic bacteria live on and within other organisms, and they obtain nutrition from their host.
b) Some parasitic bacteria cause diseases, and they are called pathogenic bacteria, while others do not cause diseases but harm the host.
c) Example: Vibrio cholerae, Diplococcus pneumoniae, etc.

C. Symbiotic Bacteria

a) Symbiotic bacteria live in close association with other living organisms so that they both benefit from each other. Neither of them is harmed.
b) Symbiotic bacteria fix atmospheric nitrogen into nitrogenous compounds which are utilized by the plants, and in return, the plant gives nutrients and protection to the bacteria.
c) Nitrogen-fixing bacteria like Rhizobium that live in the root nodules of leguminous plants are examples of symbiotic bacteria.

Fig: Heterotrophic Bacteria

Classification of Bacteria Based on Energy Source

Based on the source of energy to obtain nutrition, bacteria can be classified as:

1. Phototrophs

Bacteria that use radiant energy or light energy as their energy source are known as phototrophs. Phototrophs are again of two types depending upon the carbon source. Those phototrophs bacteria that utilize CO₂ as a carbon source are called photoautotrophs, while the bacteria that fulfil their carbon requirement by utilising organic carbon are known as photoheterotrophs.

2. Chemotrophs

Bacteria that gain energy from chemical compounds are known as chemotrophs. Those chemotrophs bacteria that utilize CO₂ as a carbon source are called chemoautotrophs, while the bacteria that fulfil their carbon requirement by utilizing organic carbon are known as chemoheterotrophs.

Fig: Flowchart of Nutrition in Bacteria

Summary

Bacteria can obtain energy and nutrients in different ways like photosynthesis, chemosynthesis, decomposing of dead organisms and wastes, and establishing mutualistic and parasitic relationships. Based on the mode of nutrition, bacteria are of two types, mainly autotrophic bacteria (can synthesise their food by themselves) and heterotrophic bacteria (not capable of synthesising their own food).

Based on the source of energy to obtain nutrition, bacteria are of two types, namely, chemotrophs and phototrophs.

FAQs on Nutrition in Bacteria

We have provided some frequently asked questions regarding Nutrition in Bacteria here:

Q.1. Which types of bacteria are responsible for nitrogen-fixing?
Ans: The bacteria having nif genes are capable of nitrogen-fixation. Such bacteria can be-living like Azotobacter or symbiotic like Rhizobium.

Q.2. What are the physical requirements for bacterial growth?
Ans: Nutrition, temperature, pH, O2 concentration, and water are some main physical requirements for bacterial growth.

Q.3. Give one example of parasitic bacteria.
Ans: Vibrio cholerae is one example of parasitic bacteria that causes the disease cholera.

Q.4. What are the types of parasitic bacteria?
Ans: Pathogenic and nonpathogenic are two types of parasitic bacteria.

Q.5. What are fastidious heterotrophs?
Ans: A few heterotrophic bacteria require a complex nutritional requirement or specific nutrients like amino acids for their survival. Such organisms are called fastidious heterotrophs.