Bacteria: Introduction, History, reproduction, cell structure , shape & size

  What is bacteria? History of bacteria Structure of bacteria Reproduction in bacteria Size and shape of bacteria.

Hello friends, you are very welcome in this post of mine, so today in this post you are going to read about bacteria, what is bacteria, how it reproduces and if you read about its cellular structure, then complete this post. read and understand what is a bacteria. 

Table of Contents

• Definition of bacteria
• History of bacteria
• Cell structure of bacteria
• Size of bacteria
• Shape of bacteria

Bacteria play an important role in our life, we get diseases by bacteria, some bacteria are beneficial to our body and some bacteria are beneficial or harmful in the fields.

Bacteria 

What is bacteria?

Bacteria are unicellular hard walled and prokaryotic microorganisms present everywhere. They are very simple in structure, they cause many types of diseases in plants and animals. The branch of science under which bacteria are studied is called bacteriology.

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History of bacteria

The credit for discovering bacteria goes to Dutch scientist Antoni VanLeeuwenhoek. With his own made microscope, he saw small creatures in the palace of his teeth, which he named animal cull. In fact it was bacteria.

Along with this, he described bacteria by

three major shapes -

spherical,

rod-shaped,

and spiral-shaped.

Because of this discovery, Antoni van Leeuwenhoek is called the father of bacteriology.

CG Arenberg first named them as bacteria.

The recognition and definition of bacteria in classification was given by Nageli, but important information about the origin and nature of bacteria was provided by Louis Pasteur. In earlier times,

it was believed that micro-organisms are self-generated through decaying matter. It was the theory of spontaneous generation which Louis Pasteur proved wrong and expressed the opinion of the origin of diseases by germs, due to which Louis Pasteur is called the father of microbiology.

And he propounded the theory of biogenesis.

Bacteria were first artificially cultured by Robert Koch. He made some rules related to the origin of diseases by bacteria, which are called Koch's postulates. He got the Nobel Prize in 1905 because of these axioms.

Robert Koch is also known as the father of modern bacteriology. More discoveries in relation to micro-organisms took place between 1885 and 1914, so this day is also called the golden age of microbiology.

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Structure of bacterial cell

The structure of the bacterial cell can be clearly seen by observing it under a microscope. Many types of components are found in bacteria like cell wall, cell membrane, capsule, flagilla, cytoplasm, ribosomes, mesosomes etc.

Capsule - Capsule is a smooth covering found outside the cell wall. Which is found in some disease causing bacteria. Capsule can be seen in microscope by special staining technique, apart from this it can also be seen by negative staining. This capsule is made of polysaccharide. If this polysaccharide is made of one type of sugar, then it is called homopolysaccharide and different sugar. When it is called heteropolysaccharide.

Examples of capsulated bacteria

-

diplococcus pneumoniae

pseudomonas aerogenous

bacillus anthracis

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Flegilla - In moving bacteria, there is a thread-like or hair-like structure which is attached to the outside of the cell wall. It is called flagella or flagellum. The diameter of flagella is 20 to 30 um and length is 15 um. It helps bacteria in movement. Bacterial flagella are many times thinner than eukaryotic.

Examples of flegilated bacteria-

vibrio cholerae

pseudomonas

spirilla

salmonella

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Cell wall - In bacteria, the semi-grid complex structure is located on the outside of the membrane on the bottom side of the capsule, which is called the cell wall, it gives a definite shape to the bacteria. The cell wall protects the plasma membrane and cytoplasmic inclusions from hostile environment. The cell wall of bacteria is made up of peptidoglycan. The cell wall of gram negative is much thinner than that of gram positive.

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Cell Membrane - Plasma membrane is called cell membrane or cytoplasmic membrane. It is located below the cell wall. The word cell membrane was given by Sina Gelli and Simmer in 1855. No cell can survive without plasma membrane. The thickness is 7.5 nanometers, it is composed of 20 to 70% proteins, 28 to 80% lipids, 50% and olivosaccharides, and 20% water.

Functions of plasma membrane -

1. Transports organic and inorganic nutrients into the cell.
2. Sides are available for attachment to the bacterial chromosome plasmid and plasmid DNA.
3. Folds inside the bacteria to form miss u som which are important for respiration.
4. Prevents harmful substances from entering the cell. It contains enzymes that work to make cell wall biosynthesis useful substances such as peptidoglycan, hyicoic acid, polysaccharide, phospholipid, lipopolysaccharide.

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Mesosomes - Mesosome - The structure formed by plasma membrane folding inwards in bacteria is called mesosome. These mesosomes are responsible for the respiration of bacteria. These mesosomes are found near the site of cell division or in the nuclear region. Mesosomes are absent in eukaryotes.

Functions of mesosome

1. They work in the respiration of bacteria.
2. Mesosomes are believed to have a role in reproduction as well.
3. It separates the bacterial DNA from each daughter cell.
4. The folding of the mesosome increases the surface area of the plasma membrane, which increases the absorption of nutrients.

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Pilli and fimbriae - pilli and fimbriae are hair-like structures found on the cell wall of bacteria. These are mostly found in gram negative bacteria like Ministers, Selector and Shivam 79. Pilli are not found in eukaryotic cells. Fimbriae refers to all the hair-like structures that cover the surface of the cell.
Pilli is genetically operated by plasmid, their number can be between 3 to 5. The number of Fimbri is around 1000. Yellow is shorter and thinner than flagella but number is more. These can be either polysaccharides on the bacterial cell or on the entire bacterial cell. They have a length of 0.2 to 20um and a diameter of 250 Å.

Functions of Pilai and Fimbri

The bacteria which contain fimbriae are called fimbriate bacteria which helps the bacteria to stick to another infected person.

fimbriae blood cells like RBC coagulates WBC.

fimbriae affects metabolic activity.

Fimbriae establish contact between two bacterial cells so that the genome of one cell can be transferred to the other cell.

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Cytoplasm - The liquid portion inside the cell in bacteria is called cytoplasm. Cytoplasm contains 80% water, proteins, carbohydrates, lipids, compounds containing organic ions, low molecules. Its cytoplasm is thick and semi-transparent. DNA molecule, ribosomes and other inclusions are found in this cytoplasm.

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Size Of bacteria

Bacteria generally have an average size of 1 to 5 µm. Spherical species of bacteria, i.e., coccus species have a diameter of 0.5 to 2.5 µm while rod-shaped species have a width of 0.2 to 2.0 µm and a length of 1.0 to 15.0 µm. The diameter of Escherichia coli ranges from 0.4 to 0.7 microns and length from 1.0 to 3.0 microns. Dialister pneumosintes is considered to be the smallest (width 16 to 45 microns and filament length several millimetres) bacteria.

Shape Of bacteria

Kohn has classified bacteria into the following types on the basis of shape –

Spherical or coccus

- These are spherical or oval and the smallest bacteria.

Rod or Bacillus

- These bacteria are rod-shaped or cylindrical. These bacteria can be movable and immovable. Most of the bacteria are of this type. Bacillus is derived from the Greek word basilum.

Vibrio or Coma

- These bacteria are shaped like English (,) like cholera or cholera causing bacteria.

Spiralized or Coiled

- These bacteria are spiralized or coiled like Spirillum.

These bacteria are also coiled or spiral shaped but their cells are flexible.