Nutrition, Respiration and Reproduction in Bacteria and Importance of Bacteria

Nutrition of Bacteria

Like other organisms, bacteria need energy for their development, maintenance, and reproduction. A lot of bacteria are heterotrophic i.e. they can not synthesize their organic substances from simple inorganic compounds. They live either as saprophytes or as parasites.

Saprophytic bacteria

They get their food from dead organic matter. Soil is full of organic substances in the form of humus. Humus is the product arising from the partial decay of plants and animals. Lots of soil populating bacteria have a really extensive enzyme system that breaks down the complex substances of humus to simpler substances.

The bacteria can then absorb and make use of these simpler substances as a source of energy. Parasitic bacteria for their nutrition are totally dependent on their host.

Some kinds of bacteria are autotrophic i.e., they can manufacture organic compounds which are essential for their survival from inorganic substances. These bacteria may be separated into two groups: photosynthetic autotrophs and chemosynthetic autotrophs.

Photosynthetic bacteria


Photosynthetic bacteria have chlorophyll which differs from the chlorophyll of green plants. Unlike the majority of green plants, which have their chlorophyll in chloroplasts, bacterial chlorophyll is dispersed in the cytoplasm. Throughout photosynthesis, the autotrophic bacteria make use of hydrogen sulfide (H2S) instead of water as a hydrogen source and liberate sulfur instead of oxygen. Green sulfur bacteria, purple sulfur bacteria, and purple non-sulfur bacteria are photosynthetic bacteria. The overall reaction of photosynthesis in photosynthetic bacteria can be written as:



Chemosynthetic bacteria

Chemosynthetic bacteria oxidize inorganic substances like ammonia, nitrate, nitrite, sulfur, or ferrous and store the energy thus released for their synthetic reactions. Nitrifying bacteria are chemosynthetic.


Respiration in Bacteria

Respiration in bacteria may be aerobic (requiring free oxygen) or anaerobic (not requiring free oxygen).

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Aerobic bacteria: Bacteria, which have the ability to grow in the presence of oxygen, are called aerobic bacteria.

Example: Pseudomonas is an aerobic bacterium.

Anaerobic bacteria: Those which can grow in the lack of oxygen are referred to as anaerobic bacteria.

Example: Spirochete is an anaerobic bacterium.

Facultative bacteria: Some bacteria are neither aerobic nor anaerobic, but facultative. These bacteria grow either in the existence or absence of oxygen.

Example: E. coli is a facultative anaerobic bacterium.

Microaerophilic bacteria: Some bacteria require a low concentration of oxygen for growth and are known as microaerophilic.

Example: Campylobacter is a microaerophilic bacterium.

Growth and Reproduction in Bacteria

Bacteria reproduce by binary fission. In this process, the bacterium, which is a single cell, divides into 2 similar daughter cells. Binary fission begins when the DNA of the bacterium divides into two (replicates). In binary fission parent cell increases in size, its chromosome duplicates, and the plasma membrane pinches inward at the center of the cell.

When a nuclear product has actually been equally distributed, the cell wall grows inward to separate cell into 2. This series is duplicated at periods by each new daughter cell which in turn increases the population of cells. When the division is complete, germs grow and establish their special functions or features.




Specific types of bacteria produce spores, either external to the vegetative cells (exospores) or within the vegetative cells (endospores). They are metabolically inactive bodies and are produced at a late-stage of cell growth. Spores are resistant to adverse physical ecological conditions such as light, heat, desiccation, pH, and chemical representatives, under beneficial conditions they sprout and form vegetative cells.


Cysts are inactive, thick-walled, desiccation resistant types, and develop throughout differentiation of vegetative cells which can sprout under appropriate conditions. They are not heat resistant.

Growth in Bacteria

Generation Time:

“The interval of time until the completion of the next division is known as generation time.”

Four unique stages are acknowledged in the bacterial development curve which is as given:

  • 1) Lag phase: It is a phase of no growth. Bacteria prepare themselves for the division.
  • 2) Log phase: It is a phase of rapid growth. Bacteria divide at an exponential rate.
  • 3) Stationary phase: Bacterial death rate is equal to the bacterial rate of reproduction and multiplication.
  • 4) Death/Decline phase: Bacteria start dying. Here the death rate is more than the reproduction rate.
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Bacteria lack standard sexual reproduction and mitosis. However, some bacteria transfer hereditary material from a donor bacterium to a recipient throughout a process called conjugation. Some conjugating bacteria use specialized sex pili to move hereditary material. Conjugation produces new hereditary mixes that may permit the resulting bacteria to survive through an excellent variety of conditions.

Importance of Bacteria
  1. Economic Value

Bacteria are economically crucial as these microbes are utilized by human beings for many purposes. The advantageous uses of bacteria include the production of standard foods such as yogurt, cheese, and vinegar. Microorganisms are also important in agriculture for compost and fertilizer production.

  1. Ecological Value

Bacteria are environmentally really essential. They are extremely versatile as a group and are found almost everywhere. They are able to disintegrate organic matter and play a significant role in the completion of cycles of nitrogen, phosphorus, sulfur, and carbon. They are important decomposers.

  1. Medical Value

Bacteria are the main producers of clinically useful antibiotics; they are used for the production of vaccines against fatal diseases; they are probiotics that enhance our health, and they are primary participants in the fermentations of dairy items and many other foods.


Frequently Asked Questions

Q1: What are saprotrophic bacteria?

Ans: The bacteria which get their food from dead or decaying organic matter are called saprotrophic bacteria.

Q2: Difference between

Photosynthetic bacteria Chemosynthetic bacteria
Synthesize their food by photosynthesis Synthesize their food by oxidizing chemical substances
The majority are parasites of green plant cells These are saprotrophic bacteria
For example: Green sulphur bacteria For example: Nitrifying bacteria


Q3: What are gram-positive and gram-negative bacteria?

Ans: Bacteria which are stained purple due to CV-1 complex formation are gram-positive and bacteria which are stained pink due to secondary dye are called gram-negative bacteria.

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Q4: In bacterial ‘growth curve’ the phase of no growth is:

  1. Lag phase B) Log phase            C) Stationary phase           D) Decline Phase

Answer: A