Bacteria: Characteristics, Occurrence, Structure, Different Shapes and Reproduction


Bacteria: Characteristics, Occurrence, Structure, Different Shapes and Reproduction

Anton Von Leeuwenhoek discovered bacteria between 1653 - 1673 with the help of a crude microscope. This was later established by Louis Pasteur (1822 - 1895). Bacteria are unicellular, procaryotic, a-chlorophyllous organisms, of microscopic size.

The largest bacteria are about 12 microns in diameter and cannot be seen without the aid of a microscope. They are ubiquitous - occurring in every natural environment - in the air, water, soil and in and on the bodies of other organisms. Bacteria even colonies the buccal cavity and alimentary canal of humans and ruminants.

Over 2000 species of bacteria have been classified and name of these only a few cause diseases in humans, animals and plants. The vast majority of bacteria are saprophytic or free-living. They are extremely important because of their effects on the human systems.

In this article, we will explain: List at least six of the general characteristics of bacteria, describe the structure of bacteria, describe reproduction and nutrition in bacteria and explain the Economic importance of bacteria.

What are Bacteria?

Bacteria are microscopic, single-celled organisms that exist in their millions, in every environment, both inside and outside other organisms. Some bacteria are harmful, but most serve a useful purpose. They support many forms of life, both plant and animal, and they are used in industrial and medicinal processes.

Bacteria are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats.


General Characteristics of Bacteria

Bacteria: Characteristics, Occurrence, Structure, Different Shapes and Reproduction

Do you remember that living organisms have features that are peculiar to them? Bacteria do have theirs. You will recall that there are over 2,000 species of bacteria. They are:

1. Generally microscopic in nature, they are single celled.

2. They may be spherical, rod-like or spiral in shape.

3. They may be motile or non-motile.

4. Aerobic or anaerobic.

5. They have no definite nucleus but chromatin granules.

6. The Cell wall is made up of chitin.

7. Some are equipped with one or more flagella.

8. They lack chlorophyll.

9. Spherical ones are about 0.5mm wide while the rod like are about 2mm - 10mm long.

10. They inhabit a wide range of natural habitats.


Occurrence of bacteria as Living Organisms

We need to also consider the occurrence of bacteria as living organisms:

1. They exist everywhere i.e. in water, air, soil and body of other organisms living or non-living.

2. They float in air or dust particles.

3. Abundant in water bodies and soil to a depth of 30cm.

4. Surplus in sewage.

5. Occur in the intestine of all animals.

6. One gram of fertile soil is estimated to contain 2.5 thousand million while lcms of fresh milk may contain more than 3000 million bacteria.


Structure of Bacterial Cell

Let us look at the structure of bacteria:

1. Bacteria are made up of complex cell wall made up of proteins and carbohydrate, sometimes impregnated with chitin.

2. No cellulose.

3. Covering the cell wall is a slime layer called the capsule or sheath. In this form they are resistant to drugs and adverse conditions.

4. There is a definite cytoplasm.

5. No clearly defined nucleus, but DNA is the nuclear material that is not bounded by a nuclear membrane.

6. Contains no membrane bound organelles.


Different Shapes of Bacteria

Bacteria: Characteristics, Occurrence, Structure, Different Shapes and Reproduction

Bacteria: Characteristics, Occurrence, Structure, Different Shapes and Reproduction

Again, let us consider different shapes of bacteria. They have four different forms. These are:

1. Cocci {Singular = Coccus}: The cells are spherical or rounded. Depending on how they cling together after cell division the cocci can further be classified as diplococci, staphylococci and streptococci.

2. Bacilli (Singular = bacillus}: The cells are rod-shaped. Some have flagella. Rod-shaped bacteria may also remain attached end-to-end as in the genus Lactobacillus.

3. Spirilla (Singular = spirillum}: The cells are spirally twisted or corksrew like. Some have flagella. Example is Treponetna.

4. Vibrio: The cells are comma-shaped Example is Yibrio cholera


Reproduction in Bacteria

You will find the process of reproduction in bacteria very interesting.

Let us now consider the details. Reproduction in Bacteria:

1. Mainly by binary fission, no sexual reproduction.

2. Binary fission occurs under favourable conditions.

3. The chromatin material divides mitotically.

4. Cytoplasm divides along with its content.

5. Two daughter bacterial cells are formed.

6. Bacillus subtilis divides 2 - 3 times in an hour.

7. A single cell may give rise to about 16 million cells in 12 hours.



We now consider this as an occurence that leads to the multiplication in the number of bacteria. 

Sporulation goes on as follows:

1.   Rod-shaped bacteria form spores as resting spores.

2.   Mass of protoplasm condenses with thick membrane (endospore).

3.   Mother cell dissolves; endospore remains dormant resisting adverse conditions e.g. freezing, dryness, high temperature etc.

4.   Under favourable conditions, new bacterial cells emerge.


Gram Reaction

The gram reaction/test developed in 1884 by Danish Biologist (Christian Gram) revealed that bacteria can be divided into two natural groups based on their reaction to the Gram's Stain.

Those bacteria which stain with gram's stain are called Gram Positive, others that do not are called Gram Negative. Gram positive bacteria such as Staphylococcus, Bacillus and Lactobacillus, develop thick walls impregnated with polysaccharides and proteins. 

The walls of Gram negative bacteria such as Salmonella, E coli and Azotobacter are thinner but more complex.

Gram positive bacteria are purple or violet after staining with Gram's stain while Gram negative bacteria are pink in colour after the staining reaction.

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