Bacteria, Biology tutorial


Anton Van Leeuwenhoek described the microbial world by employing his simple microscope in the year 1676. In the year 1820, after the innovation of compound microscope by Hooke, the bacteria appeared in the lime light. These extremely small living things were designated as 'Infusorial animalcules' or 'small microscopic species'.

Louis Pasteur (1822-95) stated a comprehensive detailed study of bacteria and proposed germ theory of disease. A German microbiologist Robert Koch was the first scientist to show the cause and effect relationship among microbes and animal diseases.

Ehrenberg (1829) was the first to make use of the word bacterium. It is the branch of study which mainly deals with bacteria and is known as Bacteriology. The bacteria are unicellular organisms and they are prokaryotic that is, they don't have a membrane bound nucleus and organelles.


Bacteria are ubiquitous in nature. They are found in all environments, where there is organic matter. They are found in soil, water, air and too in or on the bodies of plants and animals. Many bacteria live as commensals (for example: Escherichia coli in human intestine) and many as symbionts (for example: Rhizobium) in the root nodes of leguminous plants.

Features of Bacteria:

a) They are single celled and usually microscopic in nature.

b) Aerobic or Anaerobic.

c) They might be rod-like, spherical or spiral in shape.

d) They could be motile or non-motile.

e) The cell wall is made up of chitin.

f) A few are set with one or more flagella.

g) They encompass no definite nucleus however chromatin granules.

h) They are deficient in chlorophyll.

i) Bacteria inhabit a broad range of natural habitats.


Bacteria are extremely small, most being around 0.5 to 1 micron in diameter and about 3 to 5 microns in length.

Shape of Bacteria:

Nearly all elemental structural property of the bacteria is Cell morphology (shape). Cell shape is in general characteristics of a given bacteria, however can differ based on growth circumstances. Bacteria usually form distinctive cell morphologies when observed by light microscopy. The illustrations are as described below:

i) Coccus (spherical): The Coccus can be employed to explain any bacterium that consists of a spherical shape.

ii) Bacillus (rod-like): Bacillus is employed to illustrate any rod-shaped bacterium.

iii) Spirillum (spiral): This signifies to a bacterium having a spiral shape.

iv) Filamentous: It is the developments of certain bacteria, like E.coli, in which the cells carry on to elongate however don't divide.

Nutrition in Bacteria:

i) Autotrophic Bacteria: Some of the bacteria can prepare their own food and thus they are autotrophic in their manner of nutrition.

ii) Photoautotrophic bacteria: They make use of sunlight as their source of energy to prepare their food. However dissimilar photosynthetic eukaryotic cells they don't divide water to get reducing power. Thus Oxygen is not developed all through bacterial photosynthesis.

iii) Chemoautotrophic bacteria: They don't have photosynthetic pigments and thus they can't make use of sunlight energy. Instead they gain energy in the form of ATP through oxidizing organic or inorganic compounds. The energy thus acquired is utilized to reduce CO2 to organic matter.

iv) Heterotrophic Bacteria: They mainly based on other organisms (living or dead) for their food as they are not able to prepare their own food.

Respiration in Bacteria:

i) Aerobic Bacteria: These bacteria need oxygen as terminal acceptor of electrons and will not grow beneath anaerobic circumstances (that is, in the absence of O2). Several micrococcus species are obligate aerobes (that is, they should have oxygen to survive)

ii) Anaerobic bacteria: These bacteria don't make use of oxygen for growth and metabolism though gets their energy from the fermentation reaction. Illustration: Clostridium species.

iii) Capnophilic bacteria: Capnophilic bacteria are such which necessitate CO2 for growth.

iv) Facultative anaerobes: Bacteria can grow up either oxidative by employing oxygen as a terminal electron acceptor or anaerobically by employing fermentation reaction to attain energy. Bacteria which are facultative anaerobes are often termed 'aerobes'.

v) Endospores: Endospores are the structures which are building up in bacillus bacteria throughout unfavorable conditions. Luckily most of the pathogenic bacteria don't make endospores.


Reproduction through binary fission is very ordinary. It is the procedure by which most of the bacteria multiply very fast explaining the cause of spoilage of food materials, turning of milk into curd and so forth.

General sexual reproduction comprising the formation and fusion of gametes is not present in bacteria. However, gene recombination can occur in bacteria by three various methods as follows:

i) Conjugation:

In the method of gene transfer, the donor cell gets combined to the recipient cell with the assistance of pili. The pilus nurtures in size and forms the conjugation tube. The plasmid of donor cell which comprises F+ (fertility factor) experiences duplication. Merely one strand of DNA is transferred to the recipient cell through conjugation tube. The recipient accomplishes the structure of double stranded DNA by means of synthesizing the strand that complements the strand acquired from the donor.

ii) Transduction: Donor DNA is taken out in a phage coat and is relocated into the recipient through the mechanism employed for the phage infection.

iii) Transformation: The direct uptake of donor DNA through the recipient cell might be forced or natural. There are some bacterial species which are naturally competent for transformation. These species incorporate donor DNA in the linear form. The forced transformation is persuaded in the research lab, where the treatment by means of high salt and temperature shock abundant bacteria are rendered competent for the assimilation of the extra-cellular plasmids. The ability to force bacteria to integrate extra-cellular plasmids by conversion is essential for genetic Engineering.

Beneficial Activities of Bacteria:

a) Sewage disposal: The organic matter of sewage is decomposed through saprotrophic bacteria.

b) Decomposition of animal and plant remains: Saprotrophic bacteria can be employed for the decomposition and putrefy of dead bodies of plants and animals. They release gases and salts into the soil and atmosphere. Consequently such bacteria are known as nature's scavengers.

c) Soil fertility: Bacteria augment the soil with a variety of nutrients like Nitrogen and Phosphorous and enhance the quality and texture of the soil.

d) Recycling of matter: Bacteria participates a noteworthy role in cycling of elements like oxygen, carbon, sulphur and nitrogen. Hence they assist in maintaining the ecological equilibrium.

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