Bacteria - Characteristics, Occurrence, Size, Shape, Structure, Importances and Control of Bacterial Diseases

Bacteria are the most primitive, simplest and the smallest, unicellular, microscopic organisms. Bacteria were first discovered by Antony von Leeuwenhoek in 1676 A.D. He observed them in a drop of rainwater with the help of a self constructed microscope and called them little animalcules. In 1838 AD these little animalcules were given the name bacteria by Ehrenberg and in 1854 AD they were classified as plants by Cohn.

 Louis Pasteur and Robert Koch demonstrated that these organisms are responsible for some diseases of human beings, animals and plants. The science that deals with bacteria is called bacteriology.

Characteristics of Bacteria

Some important characteristics of bacteria are as follows:

• Bacteria are unicellular and microscopic.
• The bacterial cell is a prokaryotic cell, i.e. it does not contain definite nucleus bounded by nuclear membrane.
• They have a definite cell wall.
• They usually contain chlorophyll but some have bacterial chlorophyll.
• They may be heterotrophic, autotrophic or saprophytic in nutrition.
• They can synthesize vitamins.
• All the membrane bound cell organelles such as mitochondria, golgi bodies, plastids, endoplasmic reticulum, lysosomes, etc are absent in the bacterial cell.
• A large number of bacteria live as parasite and cause diseases in humans, plants and animals.

Bacteria show the characteristics of both plants as well as animals. Therefore, they are called border line between plants and animals.

Occurrence

Bacteria are found everywhere in water, air and soil. They occur in foodstuffs, fruits and vegetables. They are also found in the intestines of animals. Some species of bacteria can withstand in extreme temperature. They can grow in hot springs at very temperature. They can grow in snow of polar region. Thus, they can withstand extreme cold.

Size

Bacteria are the smallest microscopic organism varying from 0.2 micron to 20.0 micron in diameter. The average size is 1.25 um in diameter. The smallest bacterium is 0.15 to 0.31 um in length whereas the largest bacterium is 16 to 45 um in length.

[1 cm = 10mm = 10,000 um {micrometer = 10,000,000 nm (nanometer)}]

Shape

There are different shapes of bacteria. Based on their shape, the bacteria are classified into the following types:

Coccus: These are oval or spherical in shape. They occur singly, in pairs, in groups of four, in bundles or in chain.

Bacillus: These are rod shaped bacteria and are the most common amongst all the shapes. These bacteria generally occur singly but may also occur in pair or in chains.

Spirillum: These bacteria are spiral shaped with a twisted body. They also bear flagellum.

Filament or mycelia: They are thread like, aseptate and filamentous.

Structure of Bacteria

Bacteria are extremely small, unicellular and microscopic organisms. The bacterial cell contains the living substance protoplast surrounded by a non-living cell wall. A thin cell membrane lies beneath the cell wall and surrounds the cytoplasm. There is no well defined nucleus but chromatin material is present in the central region. This chromatin material is not enclosed in a nuclear membrane. The cytoplasm contains vacuoles, granules of reserve food like glycogen. Sometimes a slimy protective layer called capsule is present outside the cell wall.

Bacteria may be motile or non-motile depending upon the presence of flagella. Bacteria which possess flagella are said to be motile and can swim with the help of flagella. Bacteria which do not possess flagella are said to be non-motile. Such bacteria cannot move on their own.

Importance of Bacteria

Bacteria are of great importance to human beings. Many of them are beneficial to us whereas a large number of them are harmful.

Useful activities of Bacteria: Bacteria are useful to human in many ways.

• Bacteria like lactobacillus and acidophilus help in making curd from milk.
• They decompose waste matter into harmless substances which can then be used for manure.
• They are used in tanning of leather.
• Bacteria help to produce vinegar which is commercially used.
• They help to produce acetone and butyl alcohol.
• They help in curing and ripening of tea leaves.
• Some bacteria present in the soil converts atmospheric nitrogen into nitrates. These nitrates are used by plants to manufacture protein in plants.
• Certain types of bacteria provide vitamins of the B complex group.
•  Some bacteria are used to make antibiotics.

Harmful activities of Bacteria: Some bacteria are harmful to human, other animals and plants in different ways:

• A large number of bacteria cause diseases in humans. For example; Diplococcus pneumoniae causes pneumonia, Vibrio cholera causes cholera, Salmonella typhi causes typhoid and Mycobacterium tuberculosis causes tuberculosis.
• Bacteria cause tuberculosis of cattle, anthrax in sheep, chicken cholera and pneumonia in horses, sheep and goats.
• Some bacteria cause plant diseases. They cause leaf spots, soft roots, etc.
• Some bacteria spoil cooked food, milk, fruits, vegetables, etc. particularly during summer months.
• Certain bacteria like Clostridium botulinum causes food poisoning.
• Some bacteria like Pseudomonas denitrificans reduce the fertility of soil.

Control of Bacterial disease

Bacterial diseases in plants, human beings and animals can be controlled by following ways:

• The plant diseases are best controlled by burning the diseased plant debris.
• By employing disease free seeds
• By spraying antibacterial drugs to control bacterial diseases.
• In animals and human beings, bacterial diseases are controlled by using antibiotics.
• Persons suffering from bacterial diseases should be isolated from healthy persons.
• Vaccination is very effective method of controlling bacterial infections.